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llvm-mirror/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
Chijun Sima f6f16ab9ad [Dominators] Convert existing passes and utils to use the DomTreeUpdater class 
Summary:
This patch is the second in a series of patches related to the [[ http://lists.llvm.org/pipermail/llvm-dev/2018-June/123883.html | RFC - A new dominator tree updater for LLVM ]].

It converts passes (e.g. adce/jump-threading) and various functions which currently accept DDT in local.cpp and BasicBlockUtils.cpp to use the new DomTreeUpdater class.
These converted functions in utils can accept DomTreeUpdater with either UpdateStrategy and can deal with both DT and PDT held by the DomTreeUpdater.

Reviewers: brzycki, kuhar, dmgreen, grosser, davide

Reviewed By: brzycki

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D48967

llvm-svn: 338814
2018-08-03 05:08:17 +00:00

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112 KiB
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//===- RewriteStatepointsForGC.cpp - Make GC relocations explicit ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Rewrite call/invoke instructions so as to make potential relocations
// performed by the garbage collector explicit in the IR.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/RewriteStatepointsForGC.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/DomTreeUpdater.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Statepoint.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <set>
#include <string>
#include <utility>
#include <vector>
#define DEBUG_TYPE "rewrite-statepoints-for-gc"
using namespace llvm;
// Print the liveset found at the insert location
static cl::opt<bool> PrintLiveSet("spp-print-liveset", cl::Hidden,
cl::init(false));
static cl::opt<bool> PrintLiveSetSize("spp-print-liveset-size", cl::Hidden,
cl::init(false));
// Print out the base pointers for debugging
static cl::opt<bool> PrintBasePointers("spp-print-base-pointers", cl::Hidden,
cl::init(false));
// Cost threshold measuring when it is profitable to rematerialize value instead
// of relocating it
static cl::opt<unsigned>
RematerializationThreshold("spp-rematerialization-threshold", cl::Hidden,
cl::init(6));
#ifdef EXPENSIVE_CHECKS
static bool ClobberNonLive = true;
#else
static bool ClobberNonLive = false;
#endif
static cl::opt<bool, true> ClobberNonLiveOverride("rs4gc-clobber-non-live",
cl::location(ClobberNonLive),
cl::Hidden);
static cl::opt<bool>
AllowStatepointWithNoDeoptInfo("rs4gc-allow-statepoint-with-no-deopt-info",
cl::Hidden, cl::init(true));
/// The IR fed into RewriteStatepointsForGC may have had attributes and
/// metadata implying dereferenceability that are no longer valid/correct after
/// RewriteStatepointsForGC has run. This is because semantically, after
/// RewriteStatepointsForGC runs, all calls to gc.statepoint "free" the entire
/// heap. stripNonValidData (conservatively) restores
/// correctness by erasing all attributes in the module that externally imply
/// dereferenceability. Similar reasoning also applies to the noalias
/// attributes and metadata. gc.statepoint can touch the entire heap including
/// noalias objects.
/// Apart from attributes and metadata, we also remove instructions that imply
/// constant physical memory: llvm.invariant.start.
static void stripNonValidData(Module &M);
static bool shouldRewriteStatepointsIn(Function &F);
PreservedAnalyses RewriteStatepointsForGC::run(Module &M,
ModuleAnalysisManager &AM) {
bool Changed = false;
auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
for (Function &F : M) {
// Nothing to do for declarations.
if (F.isDeclaration() || F.empty())
continue;
// Policy choice says not to rewrite - the most common reason is that we're
// compiling code without a GCStrategy.
if (!shouldRewriteStatepointsIn(F))
continue;
auto &DT = FAM.getResult<DominatorTreeAnalysis>(F);
auto &TTI = FAM.getResult<TargetIRAnalysis>(F);
auto &TLI = FAM.getResult<TargetLibraryAnalysis>(F);
Changed |= runOnFunction(F, DT, TTI, TLI);
}
if (!Changed)
return PreservedAnalyses::all();
// stripNonValidData asserts that shouldRewriteStatepointsIn
// returns true for at least one function in the module. Since at least
// one function changed, we know that the precondition is satisfied.
stripNonValidData(M);
PreservedAnalyses PA;
PA.preserve<TargetIRAnalysis>();
PA.preserve<TargetLibraryAnalysis>();
return PA;
}
namespace {
class RewriteStatepointsForGCLegacyPass : public ModulePass {
RewriteStatepointsForGC Impl;
public:
static char ID; // Pass identification, replacement for typeid
RewriteStatepointsForGCLegacyPass() : ModulePass(ID), Impl() {
initializeRewriteStatepointsForGCLegacyPassPass(
*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override {
bool Changed = false;
const TargetLibraryInfo &TLI =
getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
for (Function &F : M) {
// Nothing to do for declarations.
if (F.isDeclaration() || F.empty())
continue;
// Policy choice says not to rewrite - the most common reason is that
// we're compiling code without a GCStrategy.
if (!shouldRewriteStatepointsIn(F))
continue;
TargetTransformInfo &TTI =
getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
Changed |= Impl.runOnFunction(F, DT, TTI, TLI);
}
if (!Changed)
return false;
// stripNonValidData asserts that shouldRewriteStatepointsIn
// returns true for at least one function in the module. Since at least
// one function changed, we know that the precondition is satisfied.
stripNonValidData(M);
return true;
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
// We add and rewrite a bunch of instructions, but don't really do much
// else. We could in theory preserve a lot more analyses here.
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
}
};
} // end anonymous namespace
char RewriteStatepointsForGCLegacyPass::ID = 0;
ModulePass *llvm::createRewriteStatepointsForGCLegacyPass() {
return new RewriteStatepointsForGCLegacyPass();
}
INITIALIZE_PASS_BEGIN(RewriteStatepointsForGCLegacyPass,
"rewrite-statepoints-for-gc",
"Make relocations explicit at statepoints", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_END(RewriteStatepointsForGCLegacyPass,
"rewrite-statepoints-for-gc",
"Make relocations explicit at statepoints", false, false)
namespace {
struct GCPtrLivenessData {
/// Values defined in this block.
MapVector<BasicBlock *, SetVector<Value *>> KillSet;
/// Values used in this block (and thus live); does not included values
/// killed within this block.
MapVector<BasicBlock *, SetVector<Value *>> LiveSet;
/// Values live into this basic block (i.e. used by any
/// instruction in this basic block or ones reachable from here)
MapVector<BasicBlock *, SetVector<Value *>> LiveIn;
/// Values live out of this basic block (i.e. live into
/// any successor block)
MapVector<BasicBlock *, SetVector<Value *>> LiveOut;
};
// The type of the internal cache used inside the findBasePointers family
// of functions. From the callers perspective, this is an opaque type and
// should not be inspected.
//
// In the actual implementation this caches two relations:
// - The base relation itself (i.e. this pointer is based on that one)
// - The base defining value relation (i.e. before base_phi insertion)
// Generally, after the execution of a full findBasePointer call, only the
// base relation will remain. Internally, we add a mixture of the two
// types, then update all the second type to the first type
using DefiningValueMapTy = MapVector<Value *, Value *>;
using StatepointLiveSetTy = SetVector<Value *>;
using RematerializedValueMapTy =
MapVector<AssertingVH<Instruction>, AssertingVH<Value>>;
struct PartiallyConstructedSafepointRecord {
/// The set of values known to be live across this safepoint
StatepointLiveSetTy LiveSet;
/// Mapping from live pointers to a base-defining-value
MapVector<Value *, Value *> PointerToBase;
/// The *new* gc.statepoint instruction itself. This produces the token
/// that normal path gc.relocates and the gc.result are tied to.
Instruction *StatepointToken;
/// Instruction to which exceptional gc relocates are attached
/// Makes it easier to iterate through them during relocationViaAlloca.
Instruction *UnwindToken;
/// Record live values we are rematerialized instead of relocating.
/// They are not included into 'LiveSet' field.
/// Maps rematerialized copy to it's original value.
RematerializedValueMapTy RematerializedValues;
};
} // end anonymous namespace
static ArrayRef<Use> GetDeoptBundleOperands(ImmutableCallSite CS) {
Optional<OperandBundleUse> DeoptBundle =
CS.getOperandBundle(LLVMContext::OB_deopt);
if (!DeoptBundle.hasValue()) {
assert(AllowStatepointWithNoDeoptInfo &&
"Found non-leaf call without deopt info!");
return None;
}
return DeoptBundle.getValue().Inputs;
}
/// Compute the live-in set for every basic block in the function
static void computeLiveInValues(DominatorTree &DT, Function &F,
GCPtrLivenessData &Data);
/// Given results from the dataflow liveness computation, find the set of live
/// Values at a particular instruction.
static void findLiveSetAtInst(Instruction *inst, GCPtrLivenessData &Data,
StatepointLiveSetTy &out);
// TODO: Once we can get to the GCStrategy, this becomes
// Optional<bool> isGCManagedPointer(const Type *Ty) const override {
static bool isGCPointerType(Type *T) {
if (auto *PT = dyn_cast<PointerType>(T))
// For the sake of this example GC, we arbitrarily pick addrspace(1) as our
// GC managed heap. We know that a pointer into this heap needs to be
// updated and that no other pointer does.
return PT->getAddressSpace() == 1;
return false;
}
// Return true if this type is one which a) is a gc pointer or contains a GC
// pointer and b) is of a type this code expects to encounter as a live value.
// (The insertion code will assert that a type which matches (a) and not (b)
// is not encountered.)
static bool isHandledGCPointerType(Type *T) {
// We fully support gc pointers
if (isGCPointerType(T))
return true;
// We partially support vectors of gc pointers. The code will assert if it
// can't handle something.
if (auto VT = dyn_cast<VectorType>(T))
if (isGCPointerType(VT->getElementType()))
return true;
return false;
}
#ifndef NDEBUG
/// Returns true if this type contains a gc pointer whether we know how to
/// handle that type or not.
static bool containsGCPtrType(Type *Ty) {
if (isGCPointerType(Ty))
return true;
if (VectorType *VT = dyn_cast<VectorType>(Ty))
return isGCPointerType(VT->getScalarType());
if (ArrayType *AT = dyn_cast<ArrayType>(Ty))
return containsGCPtrType(AT->getElementType());
if (StructType *ST = dyn_cast<StructType>(Ty))
return llvm::any_of(ST->subtypes(), containsGCPtrType);
return false;
}
// Returns true if this is a type which a) is a gc pointer or contains a GC
// pointer and b) is of a type which the code doesn't expect (i.e. first class
// aggregates). Used to trip assertions.
static bool isUnhandledGCPointerType(Type *Ty) {
return containsGCPtrType(Ty) && !isHandledGCPointerType(Ty);
}
#endif
// Return the name of the value suffixed with the provided value, or if the
// value didn't have a name, the default value specified.
static std::string suffixed_name_or(Value *V, StringRef Suffix,
StringRef DefaultName) {
return V->hasName() ? (V->getName() + Suffix).str() : DefaultName.str();
}
// Conservatively identifies any definitions which might be live at the
// given instruction. The analysis is performed immediately before the
// given instruction. Values defined by that instruction are not considered
// live. Values used by that instruction are considered live.
static void
analyzeParsePointLiveness(DominatorTree &DT,
GCPtrLivenessData &OriginalLivenessData, CallSite CS,
PartiallyConstructedSafepointRecord &Result) {
Instruction *Inst = CS.getInstruction();
StatepointLiveSetTy LiveSet;
findLiveSetAtInst(Inst, OriginalLivenessData, LiveSet);
if (PrintLiveSet) {
dbgs() << "Live Variables:\n";
for (Value *V : LiveSet)
dbgs() << " " << V->getName() << " " << *V << "\n";
}
if (PrintLiveSetSize) {
dbgs() << "Safepoint For: " << CS.getCalledValue()->getName() << "\n";
dbgs() << "Number live values: " << LiveSet.size() << "\n";
}
Result.LiveSet = LiveSet;
}
static bool isKnownBaseResult(Value *V);
namespace {
/// A single base defining value - An immediate base defining value for an
/// instruction 'Def' is an input to 'Def' whose base is also a base of 'Def'.
/// For instructions which have multiple pointer [vector] inputs or that
/// transition between vector and scalar types, there is no immediate base
/// defining value. The 'base defining value' for 'Def' is the transitive
/// closure of this relation stopping at the first instruction which has no
/// immediate base defining value. The b.d.v. might itself be a base pointer,
/// but it can also be an arbitrary derived pointer.
struct BaseDefiningValueResult {
/// Contains the value which is the base defining value.
Value * const BDV;
/// True if the base defining value is also known to be an actual base
/// pointer.
const bool IsKnownBase;
BaseDefiningValueResult(Value *BDV, bool IsKnownBase)
: BDV(BDV), IsKnownBase(IsKnownBase) {
#ifndef NDEBUG
// Check consistency between new and old means of checking whether a BDV is
// a base.
bool MustBeBase = isKnownBaseResult(BDV);
assert(!MustBeBase || MustBeBase == IsKnownBase);
#endif
}
};
} // end anonymous namespace
static BaseDefiningValueResult findBaseDefiningValue(Value *I);
/// Return a base defining value for the 'Index' element of the given vector
/// instruction 'I'. If Index is null, returns a BDV for the entire vector
/// 'I'. As an optimization, this method will try to determine when the
/// element is known to already be a base pointer. If this can be established,
/// the second value in the returned pair will be true. Note that either a
/// vector or a pointer typed value can be returned. For the former, the
/// vector returned is a BDV (and possibly a base) of the entire vector 'I'.
/// If the later, the return pointer is a BDV (or possibly a base) for the
/// particular element in 'I'.
static BaseDefiningValueResult
findBaseDefiningValueOfVector(Value *I) {
// Each case parallels findBaseDefiningValue below, see that code for
// detailed motivation.
if (isa<Argument>(I))
// An incoming argument to the function is a base pointer
return BaseDefiningValueResult(I, true);
if (isa<Constant>(I))
// Base of constant vector consists only of constant null pointers.
// For reasoning see similar case inside 'findBaseDefiningValue' function.
return BaseDefiningValueResult(ConstantAggregateZero::get(I->getType()),
true);
if (isa<LoadInst>(I))
return BaseDefiningValueResult(I, true);
if (isa<InsertElementInst>(I))
// We don't know whether this vector contains entirely base pointers or
// not. To be conservatively correct, we treat it as a BDV and will
// duplicate code as needed to construct a parallel vector of bases.
return BaseDefiningValueResult(I, false);
if (isa<ShuffleVectorInst>(I))
// We don't know whether this vector contains entirely base pointers or
// not. To be conservatively correct, we treat it as a BDV and will
// duplicate code as needed to construct a parallel vector of bases.
// TODO: There a number of local optimizations which could be applied here
// for particular sufflevector patterns.
return BaseDefiningValueResult(I, false);
// The behavior of getelementptr instructions is the same for vector and
// non-vector data types.
if (auto *GEP = dyn_cast<GetElementPtrInst>(I))
return findBaseDefiningValue(GEP->getPointerOperand());
// If the pointer comes through a bitcast of a vector of pointers to
// a vector of another type of pointer, then look through the bitcast
if (auto *BC = dyn_cast<BitCastInst>(I))
return findBaseDefiningValue(BC->getOperand(0));
// We assume that functions in the source language only return base
// pointers. This should probably be generalized via attributes to support
// both source language and internal functions.
if (isa<CallInst>(I) || isa<InvokeInst>(I))
return BaseDefiningValueResult(I, true);
// A PHI or Select is a base defining value. The outer findBasePointer
// algorithm is responsible for constructing a base value for this BDV.
assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
"unknown vector instruction - no base found for vector element");
return BaseDefiningValueResult(I, false);
}
/// Helper function for findBasePointer - Will return a value which either a)
/// defines the base pointer for the input, b) blocks the simple search
/// (i.e. a PHI or Select of two derived pointers), or c) involves a change
/// from pointer to vector type or back.
static BaseDefiningValueResult findBaseDefiningValue(Value *I) {
assert(I->getType()->isPtrOrPtrVectorTy() &&
"Illegal to ask for the base pointer of a non-pointer type");
if (I->getType()->isVectorTy())
return findBaseDefiningValueOfVector(I);
if (isa<Argument>(I))
// An incoming argument to the function is a base pointer
// We should have never reached here if this argument isn't an gc value
return BaseDefiningValueResult(I, true);
if (isa<Constant>(I)) {
// We assume that objects with a constant base (e.g. a global) can't move
// and don't need to be reported to the collector because they are always
// live. Besides global references, all kinds of constants (e.g. undef,
// constant expressions, null pointers) can be introduced by the inliner or
// the optimizer, especially on dynamically dead paths.
// Here we treat all of them as having single null base. By doing this we
// trying to avoid problems reporting various conflicts in a form of
// "phi (const1, const2)" or "phi (const, regular gc ptr)".
// See constant.ll file for relevant test cases.
return BaseDefiningValueResult(
ConstantPointerNull::get(cast<PointerType>(I->getType())), true);
}
if (CastInst *CI = dyn_cast<CastInst>(I)) {
Value *Def = CI->stripPointerCasts();
// If stripping pointer casts changes the address space there is an
// addrspacecast in between.
assert(cast<PointerType>(Def->getType())->getAddressSpace() ==
cast<PointerType>(CI->getType())->getAddressSpace() &&
"unsupported addrspacecast");
// If we find a cast instruction here, it means we've found a cast which is
// not simply a pointer cast (i.e. an inttoptr). We don't know how to
// handle int->ptr conversion.
assert(!isa<CastInst>(Def) && "shouldn't find another cast here");
return findBaseDefiningValue(Def);
}
if (isa<LoadInst>(I))
// The value loaded is an gc base itself
return BaseDefiningValueResult(I, true);
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I))
// The base of this GEP is the base
return findBaseDefiningValue(GEP->getPointerOperand());
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default:
// fall through to general call handling
break;
case Intrinsic::experimental_gc_statepoint:
llvm_unreachable("statepoints don't produce pointers");
case Intrinsic::experimental_gc_relocate:
// Rerunning safepoint insertion after safepoints are already
// inserted is not supported. It could probably be made to work,
// but why are you doing this? There's no good reason.
llvm_unreachable("repeat safepoint insertion is not supported");
case Intrinsic::gcroot:
// Currently, this mechanism hasn't been extended to work with gcroot.
// There's no reason it couldn't be, but I haven't thought about the
// implications much.
llvm_unreachable(
"interaction with the gcroot mechanism is not supported");
}
}
// We assume that functions in the source language only return base
// pointers. This should probably be generalized via attributes to support
// both source language and internal functions.
if (isa<CallInst>(I) || isa<InvokeInst>(I))
return BaseDefiningValueResult(I, true);
// TODO: I have absolutely no idea how to implement this part yet. It's not
// necessarily hard, I just haven't really looked at it yet.
assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented");
if (isa<AtomicCmpXchgInst>(I))
// A CAS is effectively a atomic store and load combined under a
// predicate. From the perspective of base pointers, we just treat it
// like a load.
return BaseDefiningValueResult(I, true);
assert(!isa<AtomicRMWInst>(I) && "Xchg handled above, all others are "
"binary ops which don't apply to pointers");
// The aggregate ops. Aggregates can either be in the heap or on the
// stack, but in either case, this is simply a field load. As a result,
// this is a defining definition of the base just like a load is.
if (isa<ExtractValueInst>(I))
return BaseDefiningValueResult(I, true);
// We should never see an insert vector since that would require we be
// tracing back a struct value not a pointer value.
assert(!isa<InsertValueInst>(I) &&
"Base pointer for a struct is meaningless");
// An extractelement produces a base result exactly when it's input does.
// We may need to insert a parallel instruction to extract the appropriate
// element out of the base vector corresponding to the input. Given this,
// it's analogous to the phi and select case even though it's not a merge.
if (isa<ExtractElementInst>(I))
// Note: There a lot of obvious peephole cases here. This are deliberately
// handled after the main base pointer inference algorithm to make writing
// test cases to exercise that code easier.
return BaseDefiningValueResult(I, false);
// The last two cases here don't return a base pointer. Instead, they
// return a value which dynamically selects from among several base
// derived pointers (each with it's own base potentially). It's the job of
// the caller to resolve these.
assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
"missing instruction case in findBaseDefiningValing");
return BaseDefiningValueResult(I, false);
}
/// Returns the base defining value for this value.
static Value *findBaseDefiningValueCached(Value *I, DefiningValueMapTy &Cache) {
Value *&Cached = Cache[I];
if (!Cached) {
Cached = findBaseDefiningValue(I).BDV;
LLVM_DEBUG(dbgs() << "fBDV-cached: " << I->getName() << " -> "
<< Cached->getName() << "\n");
}
assert(Cache[I] != nullptr);
return Cached;
}
/// Return a base pointer for this value if known. Otherwise, return it's
/// base defining value.
static Value *findBaseOrBDV(Value *I, DefiningValueMapTy &Cache) {
Value *Def = findBaseDefiningValueCached(I, Cache);
auto Found = Cache.find(Def);
if (Found != Cache.end()) {
// Either a base-of relation, or a self reference. Caller must check.
return Found->second;
}
// Only a BDV available
return Def;
}
/// Given the result of a call to findBaseDefiningValue, or findBaseOrBDV,
/// is it known to be a base pointer? Or do we need to continue searching.
static bool isKnownBaseResult(Value *V) {
if (!isa<PHINode>(V) && !isa<SelectInst>(V) &&
!isa<ExtractElementInst>(V) && !isa<InsertElementInst>(V) &&
!isa<ShuffleVectorInst>(V)) {
// no recursion possible
return true;
}
if (isa<Instruction>(V) &&
cast<Instruction>(V)->getMetadata("is_base_value")) {
// This is a previously inserted base phi or select. We know
// that this is a base value.
return true;
}
// We need to keep searching
return false;
}
namespace {
/// Models the state of a single base defining value in the findBasePointer
/// algorithm for determining where a new instruction is needed to propagate
/// the base of this BDV.
class BDVState {
public:
enum Status { Unknown, Base, Conflict };
BDVState() : BaseValue(nullptr) {}
explicit BDVState(Status Status, Value *BaseValue = nullptr)
: Status(Status), BaseValue(BaseValue) {
assert(Status != Base || BaseValue);
}
explicit BDVState(Value *BaseValue) : Status(Base), BaseValue(BaseValue) {}
Status getStatus() const { return Status; }
Value *getBaseValue() const { return BaseValue; }
bool isBase() const { return getStatus() == Base; }
bool isUnknown() const { return getStatus() == Unknown; }
bool isConflict() const { return getStatus() == Conflict; }
bool operator==(const BDVState &Other) const {
return BaseValue == Other.BaseValue && Status == Other.Status;
}
bool operator!=(const BDVState &other) const { return !(*this == other); }
LLVM_DUMP_METHOD
void dump() const {
print(dbgs());
dbgs() << '\n';
}
void print(raw_ostream &OS) const {
switch (getStatus()) {
case Unknown:
OS << "U";
break;
case Base:
OS << "B";
break;
case Conflict:
OS << "C";
break;
}
OS << " (" << getBaseValue() << " - "
<< (getBaseValue() ? getBaseValue()->getName() : "nullptr") << "): ";
}
private:
Status Status = Unknown;
AssertingVH<Value> BaseValue; // Non-null only if Status == Base.
};
} // end anonymous namespace
#ifndef NDEBUG
static raw_ostream &operator<<(raw_ostream &OS, const BDVState &State) {
State.print(OS);
return OS;
}
#endif
static BDVState meetBDVStateImpl(const BDVState &LHS, const BDVState &RHS) {
switch (LHS.getStatus()) {
case BDVState::Unknown:
return RHS;
case BDVState::Base:
assert(LHS.getBaseValue() && "can't be null");
if (RHS.isUnknown())
return LHS;
if (RHS.isBase()) {
if (LHS.getBaseValue() == RHS.getBaseValue()) {
assert(LHS == RHS && "equality broken!");
return LHS;
}
return BDVState(BDVState::Conflict);
}
assert(RHS.isConflict() && "only three states!");
return BDVState(BDVState::Conflict);
case BDVState::Conflict:
return LHS;
}
llvm_unreachable("only three states!");
}
// Values of type BDVState form a lattice, and this function implements the meet
// operation.
static BDVState meetBDVState(const BDVState &LHS, const BDVState &RHS) {
BDVState Result = meetBDVStateImpl(LHS, RHS);
assert(Result == meetBDVStateImpl(RHS, LHS) &&
"Math is wrong: meet does not commute!");
return Result;
}
/// For a given value or instruction, figure out what base ptr its derived from.
/// For gc objects, this is simply itself. On success, returns a value which is
/// the base pointer. (This is reliable and can be used for relocation.) On
/// failure, returns nullptr.
static Value *findBasePointer(Value *I, DefiningValueMapTy &Cache) {
Value *Def = findBaseOrBDV(I, Cache);
if (isKnownBaseResult(Def))
return Def;
// Here's the rough algorithm:
// - For every SSA value, construct a mapping to either an actual base
// pointer or a PHI which obscures the base pointer.
// - Construct a mapping from PHI to unknown TOP state. Use an
// optimistic algorithm to propagate base pointer information. Lattice
// looks like:
// UNKNOWN
// b1 b2 b3 b4
// CONFLICT
// When algorithm terminates, all PHIs will either have a single concrete
// base or be in a conflict state.
// - For every conflict, insert a dummy PHI node without arguments. Add
// these to the base[Instruction] = BasePtr mapping. For every
// non-conflict, add the actual base.
// - For every conflict, add arguments for the base[a] of each input
// arguments.
//
// Note: A simpler form of this would be to add the conflict form of all
// PHIs without running the optimistic algorithm. This would be
// analogous to pessimistic data flow and would likely lead to an
// overall worse solution.
#ifndef NDEBUG
auto isExpectedBDVType = [](Value *BDV) {
return isa<PHINode>(BDV) || isa<SelectInst>(BDV) ||
isa<ExtractElementInst>(BDV) || isa<InsertElementInst>(BDV) ||
isa<ShuffleVectorInst>(BDV);
};
#endif
// Once populated, will contain a mapping from each potentially non-base BDV
// to a lattice value (described above) which corresponds to that BDV.
// We use the order of insertion (DFS over the def/use graph) to provide a
// stable deterministic ordering for visiting DenseMaps (which are unordered)
// below. This is important for deterministic compilation.
MapVector<Value *, BDVState> States;
// Recursively fill in all base defining values reachable from the initial
// one for which we don't already know a definite base value for
/* scope */ {
SmallVector<Value*, 16> Worklist;
Worklist.push_back(Def);
States.insert({Def, BDVState()});
while (!Worklist.empty()) {
Value *Current = Worklist.pop_back_val();
assert(!isKnownBaseResult(Current) && "why did it get added?");
auto visitIncomingValue = [&](Value *InVal) {
Value *Base = findBaseOrBDV(InVal, Cache);
if (isKnownBaseResult(Base))
// Known bases won't need new instructions introduced and can be
// ignored safely
return;
assert(isExpectedBDVType(Base) && "the only non-base values "
"we see should be base defining values");
if (States.insert(std::make_pair(Base, BDVState())).second)
Worklist.push_back(Base);
};
if (PHINode *PN = dyn_cast<PHINode>(Current)) {
for (Value *InVal : PN->incoming_values())
visitIncomingValue(InVal);
} else if (SelectInst *SI = dyn_cast<SelectInst>(Current)) {
visitIncomingValue(SI->getTrueValue());
visitIncomingValue(SI->getFalseValue());
} else if (auto *EE = dyn_cast<ExtractElementInst>(Current)) {
visitIncomingValue(EE->getVectorOperand());
} else if (auto *IE = dyn_cast<InsertElementInst>(Current)) {
visitIncomingValue(IE->getOperand(0)); // vector operand
visitIncomingValue(IE->getOperand(1)); // scalar operand
} else if (auto *SV = dyn_cast<ShuffleVectorInst>(Current)) {
visitIncomingValue(SV->getOperand(0));
visitIncomingValue(SV->getOperand(1));
}
else {
llvm_unreachable("Unimplemented instruction case");
}
}
}
#ifndef NDEBUG
LLVM_DEBUG(dbgs() << "States after initialization:\n");
for (auto Pair : States) {
LLVM_DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n");
}
#endif
// Return a phi state for a base defining value. We'll generate a new
// base state for known bases and expect to find a cached state otherwise.
auto getStateForBDV = [&](Value *baseValue) {
if (isKnownBaseResult(baseValue))
return BDVState(baseValue);
auto I = States.find(baseValue);
assert(I != States.end() && "lookup failed!");
return I->second;
};
bool Progress = true;
while (Progress) {
#ifndef NDEBUG
const size_t OldSize = States.size();
#endif
Progress = false;
// We're only changing values in this loop, thus safe to keep iterators.
// Since this is computing a fixed point, the order of visit does not
// effect the result. TODO: We could use a worklist here and make this run
// much faster.
for (auto Pair : States) {
Value *BDV = Pair.first;
assert(!isKnownBaseResult(BDV) && "why did it get added?");
// Given an input value for the current instruction, return a BDVState
// instance which represents the BDV of that value.
auto getStateForInput = [&](Value *V) mutable {
Value *BDV = findBaseOrBDV(V, Cache);
return getStateForBDV(BDV);
};
BDVState NewState;
if (SelectInst *SI = dyn_cast<SelectInst>(BDV)) {
NewState = meetBDVState(NewState, getStateForInput(SI->getTrueValue()));
NewState =
meetBDVState(NewState, getStateForInput(SI->getFalseValue()));
} else if (PHINode *PN = dyn_cast<PHINode>(BDV)) {
for (Value *Val : PN->incoming_values())
NewState = meetBDVState(NewState, getStateForInput(Val));
} else if (auto *EE = dyn_cast<ExtractElementInst>(BDV)) {
// The 'meet' for an extractelement is slightly trivial, but it's still
// useful in that it drives us to conflict if our input is.
NewState =
meetBDVState(NewState, getStateForInput(EE->getVectorOperand()));
} else if (auto *IE = dyn_cast<InsertElementInst>(BDV)){
// Given there's a inherent type mismatch between the operands, will
// *always* produce Conflict.
NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(0)));
NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(1)));
} else {
// The only instance this does not return a Conflict is when both the
// vector operands are the same vector.
auto *SV = cast<ShuffleVectorInst>(BDV);
NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(0)));
NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(1)));
}
BDVState OldState = States[BDV];
if (OldState != NewState) {
Progress = true;
States[BDV] = NewState;
}
}
assert(OldSize == States.size() &&
"fixed point shouldn't be adding any new nodes to state");
}
#ifndef NDEBUG
LLVM_DEBUG(dbgs() << "States after meet iteration:\n");
for (auto Pair : States) {
LLVM_DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n");
}
#endif
// Insert Phis for all conflicts
// TODO: adjust naming patterns to avoid this order of iteration dependency
for (auto Pair : States) {
Instruction *I = cast<Instruction>(Pair.first);
BDVState State = Pair.second;
assert(!isKnownBaseResult(I) && "why did it get added?");
assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
// extractelement instructions are a bit special in that we may need to
// insert an extract even when we know an exact base for the instruction.
// The problem is that we need to convert from a vector base to a scalar
// base for the particular indice we're interested in.
if (State.isBase() && isa<ExtractElementInst>(I) &&
isa<VectorType>(State.getBaseValue()->getType())) {
auto *EE = cast<ExtractElementInst>(I);
// TODO: In many cases, the new instruction is just EE itself. We should
// exploit this, but can't do it here since it would break the invariant
// about the BDV not being known to be a base.
auto *BaseInst = ExtractElementInst::Create(
State.getBaseValue(), EE->getIndexOperand(), "base_ee", EE);
BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
States[I] = BDVState(BDVState::Base, BaseInst);
}
// Since we're joining a vector and scalar base, they can never be the
// same. As a result, we should always see insert element having reached
// the conflict state.
assert(!isa<InsertElementInst>(I) || State.isConflict());
if (!State.isConflict())
continue;
/// Create and insert a new instruction which will represent the base of
/// the given instruction 'I'.
auto MakeBaseInstPlaceholder = [](Instruction *I) -> Instruction* {
if (isa<PHINode>(I)) {
BasicBlock *BB = I->getParent();
int NumPreds = pred_size(BB);
assert(NumPreds > 0 && "how did we reach here");
std::string Name = suffixed_name_or(I, ".base", "base_phi");
return PHINode::Create(I->getType(), NumPreds, Name, I);
} else if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
// The undef will be replaced later
UndefValue *Undef = UndefValue::get(SI->getType());
std::string Name = suffixed_name_or(I, ".base", "base_select");
return SelectInst::Create(SI->getCondition(), Undef, Undef, Name, SI);
} else if (auto *EE = dyn_cast<ExtractElementInst>(I)) {
UndefValue *Undef = UndefValue::get(EE->getVectorOperand()->getType());
std::string Name = suffixed_name_or(I, ".base", "base_ee");
return ExtractElementInst::Create(Undef, EE->getIndexOperand(), Name,
EE);
} else if (auto *IE = dyn_cast<InsertElementInst>(I)) {
UndefValue *VecUndef = UndefValue::get(IE->getOperand(0)->getType());
UndefValue *ScalarUndef = UndefValue::get(IE->getOperand(1)->getType());
std::string Name = suffixed_name_or(I, ".base", "base_ie");
return InsertElementInst::Create(VecUndef, ScalarUndef,
IE->getOperand(2), Name, IE);
} else {
auto *SV = cast<ShuffleVectorInst>(I);
UndefValue *VecUndef = UndefValue::get(SV->getOperand(0)->getType());
std::string Name = suffixed_name_or(I, ".base", "base_sv");
return new ShuffleVectorInst(VecUndef, VecUndef, SV->getOperand(2),
Name, SV);
}
};
Instruction *BaseInst = MakeBaseInstPlaceholder(I);
// Add metadata marking this as a base value
BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
States[I] = BDVState(BDVState::Conflict, BaseInst);
}
// Returns a instruction which produces the base pointer for a given
// instruction. The instruction is assumed to be an input to one of the BDVs
// seen in the inference algorithm above. As such, we must either already
// know it's base defining value is a base, or have inserted a new
// instruction to propagate the base of it's BDV and have entered that newly
// introduced instruction into the state table. In either case, we are
// assured to be able to determine an instruction which produces it's base
// pointer.
auto getBaseForInput = [&](Value *Input, Instruction *InsertPt) {
Value *BDV = findBaseOrBDV(Input, Cache);
Value *Base = nullptr;
if (isKnownBaseResult(BDV)) {
Base = BDV;
} else {
// Either conflict or base.
assert(States.count(BDV));
Base = States[BDV].getBaseValue();
}
assert(Base && "Can't be null");
// The cast is needed since base traversal may strip away bitcasts
if (Base->getType() != Input->getType() && InsertPt)
Base = new BitCastInst(Base, Input->getType(), "cast", InsertPt);
return Base;
};
// Fixup all the inputs of the new PHIs. Visit order needs to be
// deterministic and predictable because we're naming newly created
// instructions.
for (auto Pair : States) {
Instruction *BDV = cast<Instruction>(Pair.first);
BDVState State = Pair.second;
assert(!isKnownBaseResult(BDV) && "why did it get added?");
assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
if (!State.isConflict())
continue;
if (PHINode *BasePHI = dyn_cast<PHINode>(State.getBaseValue())) {
PHINode *PN = cast<PHINode>(BDV);
unsigned NumPHIValues = PN->getNumIncomingValues();
for (unsigned i = 0; i < NumPHIValues; i++) {
Value *InVal = PN->getIncomingValue(i);
BasicBlock *InBB = PN->getIncomingBlock(i);
// If we've already seen InBB, add the same incoming value
// we added for it earlier. The IR verifier requires phi
// nodes with multiple entries from the same basic block
// to have the same incoming value for each of those
// entries. If we don't do this check here and basephi
// has a different type than base, we'll end up adding two
// bitcasts (and hence two distinct values) as incoming
// values for the same basic block.
int BlockIndex = BasePHI->getBasicBlockIndex(InBB);
if (BlockIndex != -1) {
Value *OldBase = BasePHI->getIncomingValue(BlockIndex);
BasePHI->addIncoming(OldBase, InBB);
#ifndef NDEBUG
Value *Base = getBaseForInput(InVal, nullptr);
// In essence this assert states: the only way two values
// incoming from the same basic block may be different is by
// being different bitcasts of the same value. A cleanup
// that remains TODO is changing findBaseOrBDV to return an
// llvm::Value of the correct type (and still remain pure).
// This will remove the need to add bitcasts.
assert(Base->stripPointerCasts() == OldBase->stripPointerCasts() &&
"Sanity -- findBaseOrBDV should be pure!");
#endif
continue;
}
// Find the instruction which produces the base for each input. We may
// need to insert a bitcast in the incoming block.
// TODO: Need to split critical edges if insertion is needed
Value *Base = getBaseForInput(InVal, InBB->getTerminator());
BasePHI->addIncoming(Base, InBB);
}
assert(BasePHI->getNumIncomingValues() == NumPHIValues);
} else if (SelectInst *BaseSI =
dyn_cast<SelectInst>(State.getBaseValue())) {
SelectInst *SI = cast<SelectInst>(BDV);
// Find the instruction which produces the base for each input.
// We may need to insert a bitcast.
BaseSI->setTrueValue(getBaseForInput(SI->getTrueValue(), BaseSI));
BaseSI->setFalseValue(getBaseForInput(SI->getFalseValue(), BaseSI));
} else if (auto *BaseEE =
dyn_cast<ExtractElementInst>(State.getBaseValue())) {
Value *InVal = cast<ExtractElementInst>(BDV)->getVectorOperand();
// Find the instruction which produces the base for each input. We may
// need to insert a bitcast.
BaseEE->setOperand(0, getBaseForInput(InVal, BaseEE));
} else if (auto *BaseIE = dyn_cast<InsertElementInst>(State.getBaseValue())){
auto *BdvIE = cast<InsertElementInst>(BDV);
auto UpdateOperand = [&](int OperandIdx) {
Value *InVal = BdvIE->getOperand(OperandIdx);
Value *Base = getBaseForInput(InVal, BaseIE);
BaseIE->setOperand(OperandIdx, Base);
};
UpdateOperand(0); // vector operand
UpdateOperand(1); // scalar operand
} else {
auto *BaseSV = cast<ShuffleVectorInst>(State.getBaseValue());
auto *BdvSV = cast<ShuffleVectorInst>(BDV);
auto UpdateOperand = [&](int OperandIdx) {
Value *InVal = BdvSV->getOperand(OperandIdx);
Value *Base = getBaseForInput(InVal, BaseSV);
BaseSV->setOperand(OperandIdx, Base);
};
UpdateOperand(0); // vector operand
UpdateOperand(1); // vector operand
}
}
// Cache all of our results so we can cheaply reuse them
// NOTE: This is actually two caches: one of the base defining value
// relation and one of the base pointer relation! FIXME
for (auto Pair : States) {
auto *BDV = Pair.first;
Value *Base = Pair.second.getBaseValue();
assert(BDV && Base);
assert(!isKnownBaseResult(BDV) && "why did it get added?");
LLVM_DEBUG(
dbgs() << "Updating base value cache"
<< " for: " << BDV->getName() << " from: "
<< (Cache.count(BDV) ? Cache[BDV]->getName().str() : "none")
<< " to: " << Base->getName() << "\n");
if (Cache.count(BDV)) {
assert(isKnownBaseResult(Base) &&
"must be something we 'know' is a base pointer");
// Once we transition from the BDV relation being store in the Cache to
// the base relation being stored, it must be stable
assert((!isKnownBaseResult(Cache[BDV]) || Cache[BDV] == Base) &&
"base relation should be stable");
}
Cache[BDV] = Base;
}
assert(Cache.count(Def));
return Cache[Def];
}
// For a set of live pointers (base and/or derived), identify the base
// pointer of the object which they are derived from. This routine will
// mutate the IR graph as needed to make the 'base' pointer live at the
// definition site of 'derived'. This ensures that any use of 'derived' can
// also use 'base'. This may involve the insertion of a number of
// additional PHI nodes.
//
// preconditions: live is a set of pointer type Values
//
// side effects: may insert PHI nodes into the existing CFG, will preserve
// CFG, will not remove or mutate any existing nodes
//
// post condition: PointerToBase contains one (derived, base) pair for every
// pointer in live. Note that derived can be equal to base if the original
// pointer was a base pointer.
static void
findBasePointers(const StatepointLiveSetTy &live,
MapVector<Value *, Value *> &PointerToBase,
DominatorTree *DT, DefiningValueMapTy &DVCache) {
for (Value *ptr : live) {
Value *base = findBasePointer(ptr, DVCache);
assert(base && "failed to find base pointer");
PointerToBase[ptr] = base;
assert((!isa<Instruction>(base) || !isa<Instruction>(ptr) ||
DT->dominates(cast<Instruction>(base)->getParent(),
cast<Instruction>(ptr)->getParent())) &&
"The base we found better dominate the derived pointer");
}
}
/// Find the required based pointers (and adjust the live set) for the given
/// parse point.
static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache,
CallSite CS,
PartiallyConstructedSafepointRecord &result) {
MapVector<Value *, Value *> PointerToBase;
findBasePointers(result.LiveSet, PointerToBase, &DT, DVCache);
if (PrintBasePointers) {
errs() << "Base Pairs (w/o Relocation):\n";
for (auto &Pair : PointerToBase) {
errs() << " derived ";
Pair.first->printAsOperand(errs(), false);
errs() << " base ";
Pair.second->printAsOperand(errs(), false);
errs() << "\n";;
}
}
result.PointerToBase = PointerToBase;
}
/// Given an updated version of the dataflow liveness results, update the
/// liveset and base pointer maps for the call site CS.
static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
CallSite CS,
PartiallyConstructedSafepointRecord &result);
static void recomputeLiveInValues(
Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate,
MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
// TODO-PERF: reuse the original liveness, then simply run the dataflow
// again. The old values are still live and will help it stabilize quickly.
GCPtrLivenessData RevisedLivenessData;
computeLiveInValues(DT, F, RevisedLivenessData);
for (size_t i = 0; i < records.size(); i++) {
struct PartiallyConstructedSafepointRecord &info = records[i];
recomputeLiveInValues(RevisedLivenessData, toUpdate[i], info);
}
}
// When inserting gc.relocate and gc.result calls, we need to ensure there are
// no uses of the original value / return value between the gc.statepoint and
// the gc.relocate / gc.result call. One case which can arise is a phi node
// starting one of the successor blocks. We also need to be able to insert the
// gc.relocates only on the path which goes through the statepoint. We might
// need to split an edge to make this possible.
static BasicBlock *
normalizeForInvokeSafepoint(BasicBlock *BB, BasicBlock *InvokeParent,
DominatorTree &DT) {
BasicBlock *Ret = BB;
if (!BB->getUniquePredecessor())
Ret = SplitBlockPredecessors(BB, InvokeParent, "", &DT);
// Now that 'Ret' has unique predecessor we can safely remove all phi nodes
// from it
FoldSingleEntryPHINodes(Ret);
assert(!isa<PHINode>(Ret->begin()) &&
"All PHI nodes should have been removed!");
// At this point, we can safely insert a gc.relocate or gc.result as the first
// instruction in Ret if needed.
return Ret;
}
// Create new attribute set containing only attributes which can be transferred
// from original call to the safepoint.
static AttributeList legalizeCallAttributes(AttributeList AL) {
if (AL.isEmpty())
return AL;
// Remove the readonly, readnone, and statepoint function attributes.
AttrBuilder FnAttrs = AL.getFnAttributes();
FnAttrs.removeAttribute(Attribute::ReadNone);
FnAttrs.removeAttribute(Attribute::ReadOnly);
for (Attribute A : AL.getFnAttributes()) {
if (isStatepointDirectiveAttr(A))
FnAttrs.remove(A);
}
// Just skip parameter and return attributes for now
LLVMContext &Ctx = AL.getContext();
return AttributeList::get(Ctx, AttributeList::FunctionIndex,
AttributeSet::get(Ctx, FnAttrs));
}
/// Helper function to place all gc relocates necessary for the given
/// statepoint.
/// Inputs:
/// liveVariables - list of variables to be relocated.
/// liveStart - index of the first live variable.
/// basePtrs - base pointers.
/// statepointToken - statepoint instruction to which relocates should be
/// bound.
/// Builder - Llvm IR builder to be used to construct new calls.
static void CreateGCRelocates(ArrayRef<Value *> LiveVariables,
const int LiveStart,
ArrayRef<Value *> BasePtrs,
Instruction *StatepointToken,
IRBuilder<> Builder) {
if (LiveVariables.empty())
return;
auto FindIndex = [](ArrayRef<Value *> LiveVec, Value *Val) {
auto ValIt = llvm::find(LiveVec, Val);
assert(ValIt != LiveVec.end() && "Val not found in LiveVec!");
size_t Index = std::distance(LiveVec.begin(), ValIt);
assert(Index < LiveVec.size() && "Bug in std::find?");
return Index;
};
Module *M = StatepointToken->getModule();
// All gc_relocate are generated as i8 addrspace(1)* (or a vector type whose
// element type is i8 addrspace(1)*). We originally generated unique
// declarations for each pointer type, but this proved problematic because
// the intrinsic mangling code is incomplete and fragile. Since we're moving
// towards a single unified pointer type anyways, we can just cast everything
// to an i8* of the right address space. A bitcast is added later to convert
// gc_relocate to the actual value's type.
auto getGCRelocateDecl = [&] (Type *Ty) {
assert(isHandledGCPointerType(Ty));
auto AS = Ty->getScalarType()->getPointerAddressSpace();
Type *NewTy = Type::getInt8PtrTy(M->getContext(), AS);
if (auto *VT = dyn_cast<VectorType>(Ty))
NewTy = VectorType::get(NewTy, VT->getNumElements());
return Intrinsic::getDeclaration(M, Intrinsic::experimental_gc_relocate,
{NewTy});
};
// Lazily populated map from input types to the canonicalized form mentioned
// in the comment above. This should probably be cached somewhere more
// broadly.
DenseMap<Type*, Value*> TypeToDeclMap;
for (unsigned i = 0; i < LiveVariables.size(); i++) {
// Generate the gc.relocate call and save the result
Value *BaseIdx =
Builder.getInt32(LiveStart + FindIndex(LiveVariables, BasePtrs[i]));
Value *LiveIdx = Builder.getInt32(LiveStart + i);
Type *Ty = LiveVariables[i]->getType();
if (!TypeToDeclMap.count(Ty))
TypeToDeclMap[Ty] = getGCRelocateDecl(Ty);
Value *GCRelocateDecl = TypeToDeclMap[Ty];
// only specify a debug name if we can give a useful one
CallInst *Reloc = Builder.CreateCall(
GCRelocateDecl, {StatepointToken, BaseIdx, LiveIdx},
suffixed_name_or(LiveVariables[i], ".relocated", ""));
// Trick CodeGen into thinking there are lots of free registers at this
// fake call.
Reloc->setCallingConv(CallingConv::Cold);
}
}
namespace {
/// This struct is used to defer RAUWs and `eraseFromParent` s. Using this
/// avoids having to worry about keeping around dangling pointers to Values.
class DeferredReplacement {
AssertingVH<Instruction> Old;
AssertingVH<Instruction> New;
bool IsDeoptimize = false;
DeferredReplacement() = default;
public:
static DeferredReplacement createRAUW(Instruction *Old, Instruction *New) {
assert(Old != New && Old && New &&
"Cannot RAUW equal values or to / from null!");
DeferredReplacement D;
D.Old = Old;
D.New = New;
return D;
}
static DeferredReplacement createDelete(Instruction *ToErase) {
DeferredReplacement D;
D.Old = ToErase;
return D;
}
static DeferredReplacement createDeoptimizeReplacement(Instruction *Old) {
#ifndef NDEBUG
auto *F = cast<CallInst>(Old)->getCalledFunction();
assert(F && F->getIntrinsicID() == Intrinsic::experimental_deoptimize &&
"Only way to construct a deoptimize deferred replacement");
#endif
DeferredReplacement D;
D.Old = Old;
D.IsDeoptimize = true;
return D;
}
/// Does the task represented by this instance.
void doReplacement() {
Instruction *OldI = Old;
Instruction *NewI = New;
assert(OldI != NewI && "Disallowed at construction?!");
assert((!IsDeoptimize || !New) &&
"Deoptimize intrinsics are not replaced!");
Old = nullptr;
New = nullptr;
if (NewI)
OldI->replaceAllUsesWith(NewI);
if (IsDeoptimize) {
// Note: we've inserted instructions, so the call to llvm.deoptimize may
// not necessarily be followed by the matching return.
auto *RI = cast<ReturnInst>(OldI->getParent()->getTerminator());
new UnreachableInst(RI->getContext(), RI);
RI->eraseFromParent();
}
OldI->eraseFromParent();
}
};
} // end anonymous namespace
static StringRef getDeoptLowering(CallSite CS) {
const char *DeoptLowering = "deopt-lowering";
if (CS.hasFnAttr(DeoptLowering)) {
// FIXME: CallSite has a *really* confusing interface around attributes
// with values.
const AttributeList &CSAS = CS.getAttributes();
if (CSAS.hasAttribute(AttributeList::FunctionIndex, DeoptLowering))
return CSAS.getAttribute(AttributeList::FunctionIndex, DeoptLowering)
.getValueAsString();
Function *F = CS.getCalledFunction();
assert(F && F->hasFnAttribute(DeoptLowering));
return F->getFnAttribute(DeoptLowering).getValueAsString();
}
return "live-through";
}
static void
makeStatepointExplicitImpl(const CallSite CS, /* to replace */
const SmallVectorImpl<Value *> &BasePtrs,
const SmallVectorImpl<Value *> &LiveVariables,
PartiallyConstructedSafepointRecord &Result,
std::vector<DeferredReplacement> &Replacements) {
assert(BasePtrs.size() == LiveVariables.size());
// Then go ahead and use the builder do actually do the inserts. We insert
// immediately before the previous instruction under the assumption that all
// arguments will be available here. We can't insert afterwards since we may
// be replacing a terminator.
Instruction *InsertBefore = CS.getInstruction();
IRBuilder<> Builder(InsertBefore);
ArrayRef<Value *> GCArgs(LiveVariables);
uint64_t StatepointID = StatepointDirectives::DefaultStatepointID;
uint32_t NumPatchBytes = 0;
uint32_t Flags = uint32_t(StatepointFlags::None);
ArrayRef<Use> CallArgs(CS.arg_begin(), CS.arg_end());
ArrayRef<Use> DeoptArgs = GetDeoptBundleOperands(CS);
ArrayRef<Use> TransitionArgs;
if (auto TransitionBundle =
CS.getOperandBundle(LLVMContext::OB_gc_transition)) {
Flags |= uint32_t(StatepointFlags::GCTransition);
TransitionArgs = TransitionBundle->Inputs;
}
// Instead of lowering calls to @llvm.experimental.deoptimize as normal calls
// with a return value, we lower then as never returning calls to
// __llvm_deoptimize that are followed by unreachable to get better codegen.
bool IsDeoptimize = false;
StatepointDirectives SD =
parseStatepointDirectivesFromAttrs(CS.getAttributes());
if (SD.NumPatchBytes)
NumPatchBytes = *SD.NumPatchBytes;
if (SD.StatepointID)
StatepointID = *SD.StatepointID;
// Pass through the requested lowering if any. The default is live-through.
StringRef DeoptLowering = getDeoptLowering(CS);
if (DeoptLowering.equals("live-in"))
Flags |= uint32_t(StatepointFlags::DeoptLiveIn);
else {
assert(DeoptLowering.equals("live-through") && "Unsupported value!");
}
Value *CallTarget = CS.getCalledValue();
if (Function *F = dyn_cast<Function>(CallTarget)) {
if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize) {
// Calls to llvm.experimental.deoptimize are lowered to calls to the
// __llvm_deoptimize symbol. We want to resolve this now, since the
// verifier does not allow taking the address of an intrinsic function.
SmallVector<Type *, 8> DomainTy;
for (Value *Arg : CallArgs)
DomainTy.push_back(Arg->getType());
auto *FTy = FunctionType::get(Type::getVoidTy(F->getContext()), DomainTy,
/* isVarArg = */ false);
// Note: CallTarget can be a bitcast instruction of a symbol if there are
// calls to @llvm.experimental.deoptimize with different argument types in
// the same module. This is fine -- we assume the frontend knew what it
// was doing when generating this kind of IR.
CallTarget =
F->getParent()->getOrInsertFunction("__llvm_deoptimize", FTy);
IsDeoptimize = true;
}
}
// Create the statepoint given all the arguments
Instruction *Token = nullptr;
if (CS.isCall()) {
CallInst *ToReplace = cast<CallInst>(CS.getInstruction());
CallInst *Call = Builder.CreateGCStatepointCall(
StatepointID, NumPatchBytes, CallTarget, Flags, CallArgs,
TransitionArgs, DeoptArgs, GCArgs, "safepoint_token");
Call->setTailCallKind(ToReplace->getTailCallKind());
Call->setCallingConv(ToReplace->getCallingConv());
// Currently we will fail on parameter attributes and on certain
// function attributes. In case if we can handle this set of attributes -
// set up function attrs directly on statepoint and return attrs later for
// gc_result intrinsic.
Call->setAttributes(legalizeCallAttributes(ToReplace->getAttributes()));
Token = Call;
// Put the following gc_result and gc_relocate calls immediately after the
// the old call (which we're about to delete)
assert(ToReplace->getNextNode() && "Not a terminator, must have next!");
Builder.SetInsertPoint(ToReplace->getNextNode());
Builder.SetCurrentDebugLocation(ToReplace->getNextNode()->getDebugLoc());
} else {
InvokeInst *ToReplace = cast<InvokeInst>(CS.getInstruction());
// Insert the new invoke into the old block. We'll remove the old one in a
// moment at which point this will become the new terminator for the
// original block.
InvokeInst *Invoke = Builder.CreateGCStatepointInvoke(
StatepointID, NumPatchBytes, CallTarget, ToReplace->getNormalDest(),
ToReplace->getUnwindDest(), Flags, CallArgs, TransitionArgs, DeoptArgs,
GCArgs, "statepoint_token");
Invoke->setCallingConv(ToReplace->getCallingConv());
// Currently we will fail on parameter attributes and on certain
// function attributes. In case if we can handle this set of attributes -
// set up function attrs directly on statepoint and return attrs later for
// gc_result intrinsic.
Invoke->setAttributes(legalizeCallAttributes(ToReplace->getAttributes()));
Token = Invoke;
// Generate gc relocates in exceptional path
BasicBlock *UnwindBlock = ToReplace->getUnwindDest();
assert(!isa<PHINode>(UnwindBlock->begin()) &&
UnwindBlock->getUniquePredecessor() &&
"can't safely insert in this block!");
Builder.SetInsertPoint(&*UnwindBlock->getFirstInsertionPt());
Builder.SetCurrentDebugLocation(ToReplace->getDebugLoc());
// Attach exceptional gc relocates to the landingpad.
Instruction *ExceptionalToken = UnwindBlock->getLandingPadInst();
Result.UnwindToken = ExceptionalToken;
const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx();
CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, ExceptionalToken,
Builder);
// Generate gc relocates and returns for normal block
BasicBlock *NormalDest = ToReplace->getNormalDest();
assert(!isa<PHINode>(NormalDest->begin()) &&
NormalDest->getUniquePredecessor() &&
"can't safely insert in this block!");
Builder.SetInsertPoint(&*NormalDest->getFirstInsertionPt());
// gc relocates will be generated later as if it were regular call
// statepoint
}
assert(Token && "Should be set in one of the above branches!");
if (IsDeoptimize) {
// If we're wrapping an @llvm.experimental.deoptimize in a statepoint, we
// transform the tail-call like structure to a call to a void function
// followed by unreachable to get better codegen.
Replacements.push_back(
DeferredReplacement::createDeoptimizeReplacement(CS.getInstruction()));
} else {
Token->setName("statepoint_token");
if (!CS.getType()->isVoidTy() && !CS.getInstruction()->use_empty()) {
StringRef Name =
CS.getInstruction()->hasName() ? CS.getInstruction()->getName() : "";
CallInst *GCResult = Builder.CreateGCResult(Token, CS.getType(), Name);
GCResult->setAttributes(
AttributeList::get(GCResult->getContext(), AttributeList::ReturnIndex,
CS.getAttributes().getRetAttributes()));
// We cannot RAUW or delete CS.getInstruction() because it could be in the
// live set of some other safepoint, in which case that safepoint's
// PartiallyConstructedSafepointRecord will hold a raw pointer to this
// llvm::Instruction. Instead, we defer the replacement and deletion to
// after the live sets have been made explicit in the IR, and we no longer
// have raw pointers to worry about.
Replacements.emplace_back(
DeferredReplacement::createRAUW(CS.getInstruction(), GCResult));
} else {
Replacements.emplace_back(
DeferredReplacement::createDelete(CS.getInstruction()));
}
}
Result.StatepointToken = Token;
// Second, create a gc.relocate for every live variable
const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx();
CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, Token, Builder);
}
// Replace an existing gc.statepoint with a new one and a set of gc.relocates
// which make the relocations happening at this safepoint explicit.
//
// WARNING: Does not do any fixup to adjust users of the original live
// values. That's the callers responsibility.
static void
makeStatepointExplicit(DominatorTree &DT, CallSite CS,
PartiallyConstructedSafepointRecord &Result,
std::vector<DeferredReplacement> &Replacements) {
const auto &LiveSet = Result.LiveSet;
const auto &PointerToBase = Result.PointerToBase;
// Convert to vector for efficient cross referencing.
SmallVector<Value *, 64> BaseVec, LiveVec;
LiveVec.reserve(LiveSet.size());
BaseVec.reserve(LiveSet.size());
for (Value *L : LiveSet) {
LiveVec.push_back(L);
assert(PointerToBase.count(L));
Value *Base = PointerToBase.find(L)->second;
BaseVec.push_back(Base);
}
assert(LiveVec.size() == BaseVec.size());
// Do the actual rewriting and delete the old statepoint
makeStatepointExplicitImpl(CS, BaseVec, LiveVec, Result, Replacements);
}
// Helper function for the relocationViaAlloca.
//
// It receives iterator to the statepoint gc relocates and emits a store to the
// assigned location (via allocaMap) for the each one of them. It adds the
// visited values into the visitedLiveValues set, which we will later use them
// for sanity checking.
static void
insertRelocationStores(iterator_range<Value::user_iterator> GCRelocs,
DenseMap<Value *, Value *> &AllocaMap,
DenseSet<Value *> &VisitedLiveValues) {
for (User *U : GCRelocs) {
GCRelocateInst *Relocate = dyn_cast<GCRelocateInst>(U);
if (!Relocate)
continue;
Value *OriginalValue = Relocate->getDerivedPtr();
assert(AllocaMap.count(OriginalValue));
Value *Alloca = AllocaMap[OriginalValue];
// Emit store into the related alloca
// All gc_relocates are i8 addrspace(1)* typed, and it must be bitcasted to
// the correct type according to alloca.
assert(Relocate->getNextNode() &&
"Should always have one since it's not a terminator");
IRBuilder<> Builder(Relocate->getNextNode());
Value *CastedRelocatedValue =
Builder.CreateBitCast(Relocate,
cast<AllocaInst>(Alloca)->getAllocatedType(),
suffixed_name_or(Relocate, ".casted", ""));
StoreInst *Store = new StoreInst(CastedRelocatedValue, Alloca);
Store->insertAfter(cast<Instruction>(CastedRelocatedValue));
#ifndef NDEBUG
VisitedLiveValues.insert(OriginalValue);
#endif
}
}
// Helper function for the "relocationViaAlloca". Similar to the
// "insertRelocationStores" but works for rematerialized values.
static void insertRematerializationStores(
const RematerializedValueMapTy &RematerializedValues,
DenseMap<Value *, Value *> &AllocaMap,
DenseSet<Value *> &VisitedLiveValues) {
for (auto RematerializedValuePair: RematerializedValues) {
Instruction *RematerializedValue = RematerializedValuePair.first;
Value *OriginalValue = RematerializedValuePair.second;
assert(AllocaMap.count(OriginalValue) &&
"Can not find alloca for rematerialized value");
Value *Alloca = AllocaMap[OriginalValue];
StoreInst *Store = new StoreInst(RematerializedValue, Alloca);
Store->insertAfter(RematerializedValue);
#ifndef NDEBUG
VisitedLiveValues.insert(OriginalValue);
#endif
}
}
/// Do all the relocation update via allocas and mem2reg
static void relocationViaAlloca(
Function &F, DominatorTree &DT, ArrayRef<Value *> Live,
ArrayRef<PartiallyConstructedSafepointRecord> Records) {
#ifndef NDEBUG
// record initial number of (static) allocas; we'll check we have the same
// number when we get done.
int InitialAllocaNum = 0;
for (Instruction &I : F.getEntryBlock())
if (isa<AllocaInst>(I))
InitialAllocaNum++;
#endif
// TODO-PERF: change data structures, reserve
DenseMap<Value *, Value *> AllocaMap;
SmallVector<AllocaInst *, 200> PromotableAllocas;
// Used later to chack that we have enough allocas to store all values
std::size_t NumRematerializedValues = 0;
PromotableAllocas.reserve(Live.size());
// Emit alloca for "LiveValue" and record it in "allocaMap" and
// "PromotableAllocas"
const DataLayout &DL = F.getParent()->getDataLayout();
auto emitAllocaFor = [&](Value *LiveValue) {
AllocaInst *Alloca = new AllocaInst(LiveValue->getType(),
DL.getAllocaAddrSpace(), "",
F.getEntryBlock().getFirstNonPHI());
AllocaMap[LiveValue] = Alloca;
PromotableAllocas.push_back(Alloca);
};
// Emit alloca for each live gc pointer
for (Value *V : Live)
emitAllocaFor(V);
// Emit allocas for rematerialized values
for (const auto &Info : Records)
for (auto RematerializedValuePair : Info.RematerializedValues) {
Value *OriginalValue = RematerializedValuePair.second;
if (AllocaMap.count(OriginalValue) != 0)
continue;
emitAllocaFor(OriginalValue);
++NumRematerializedValues;
}
// The next two loops are part of the same conceptual operation. We need to
// insert a store to the alloca after the original def and at each
// redefinition. We need to insert a load before each use. These are split
// into distinct loops for performance reasons.
// Update gc pointer after each statepoint: either store a relocated value or
// null (if no relocated value was found for this gc pointer and it is not a
// gc_result). This must happen before we update the statepoint with load of
// alloca otherwise we lose the link between statepoint and old def.
for (const auto &Info : Records) {
Value *Statepoint = Info.StatepointToken;
// This will be used for consistency check
DenseSet<Value *> VisitedLiveValues;
// Insert stores for normal statepoint gc relocates
insertRelocationStores(Statepoint->users(), AllocaMap, VisitedLiveValues);
// In case if it was invoke statepoint
// we will insert stores for exceptional path gc relocates.
if (isa<InvokeInst>(Statepoint)) {
insertRelocationStores(Info.UnwindToken->users(), AllocaMap,
VisitedLiveValues);
}
// Do similar thing with rematerialized values
insertRematerializationStores(Info.RematerializedValues, AllocaMap,
VisitedLiveValues);
if (ClobberNonLive) {
// As a debugging aid, pretend that an unrelocated pointer becomes null at
// the gc.statepoint. This will turn some subtle GC problems into
// slightly easier to debug SEGVs. Note that on large IR files with
// lots of gc.statepoints this is extremely costly both memory and time
// wise.
SmallVector<AllocaInst *, 64> ToClobber;
for (auto Pair : AllocaMap) {
Value *Def = Pair.first;
AllocaInst *Alloca = cast<AllocaInst>(Pair.second);
// This value was relocated
if (VisitedLiveValues.count(Def)) {
continue;
}
ToClobber.push_back(Alloca);
}
auto InsertClobbersAt = [&](Instruction *IP) {
for (auto *AI : ToClobber) {
auto PT = cast<PointerType>(AI->getAllocatedType());
Constant *CPN = ConstantPointerNull::get(PT);
StoreInst *Store = new StoreInst(CPN, AI);
Store->insertBefore(IP);
}
};
// Insert the clobbering stores. These may get intermixed with the
// gc.results and gc.relocates, but that's fine.
if (auto II = dyn_cast<InvokeInst>(Statepoint)) {
InsertClobbersAt(&*II->getNormalDest()->getFirstInsertionPt());
InsertClobbersAt(&*II->getUnwindDest()->getFirstInsertionPt());
} else {
InsertClobbersAt(cast<Instruction>(Statepoint)->getNextNode());
}
}
}
// Update use with load allocas and add store for gc_relocated.
for (auto Pair : AllocaMap) {
Value *Def = Pair.first;
Value *Alloca = Pair.second;
// We pre-record the uses of allocas so that we dont have to worry about
// later update that changes the user information..
SmallVector<Instruction *, 20> Uses;
// PERF: trade a linear scan for repeated reallocation
Uses.reserve(Def->getNumUses());
for (User *U : Def->users()) {
if (!isa<ConstantExpr>(U)) {
// If the def has a ConstantExpr use, then the def is either a
// ConstantExpr use itself or null. In either case
// (recursively in the first, directly in the second), the oop
// it is ultimately dependent on is null and this particular
// use does not need to be fixed up.
Uses.push_back(cast<Instruction>(U));
}
}
llvm::sort(Uses.begin(), Uses.end());
auto Last = std::unique(Uses.begin(), Uses.end());
Uses.erase(Last, Uses.end());
for (Instruction *Use : Uses) {
if (isa<PHINode>(Use)) {
PHINode *Phi = cast<PHINode>(Use);
for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++) {
if (Def == Phi->getIncomingValue(i)) {
LoadInst *Load = new LoadInst(
Alloca, "", Phi->getIncomingBlock(i)->getTerminator());
Phi->setIncomingValue(i, Load);
}
}
} else {
LoadInst *Load = new LoadInst(Alloca, "", Use);
Use->replaceUsesOfWith(Def, Load);
}
}
// Emit store for the initial gc value. Store must be inserted after load,
// otherwise store will be in alloca's use list and an extra load will be
// inserted before it.
StoreInst *Store = new StoreInst(Def, Alloca);
if (Instruction *Inst = dyn_cast<Instruction>(Def)) {
if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Inst)) {
// InvokeInst is a TerminatorInst so the store need to be inserted
// into its normal destination block.
BasicBlock *NormalDest = Invoke->getNormalDest();
Store->insertBefore(NormalDest->getFirstNonPHI());
} else {
assert(!Inst->isTerminator() &&
"The only TerminatorInst that can produce a value is "
"InvokeInst which is handled above.");
Store->insertAfter(Inst);
}
} else {
assert(isa<Argument>(Def));
Store->insertAfter(cast<Instruction>(Alloca));
}
}
assert(PromotableAllocas.size() == Live.size() + NumRematerializedValues &&
"we must have the same allocas with lives");
if (!PromotableAllocas.empty()) {
// Apply mem2reg to promote alloca to SSA
PromoteMemToReg(PromotableAllocas, DT);
}
#ifndef NDEBUG
for (auto &I : F.getEntryBlock())
if (isa<AllocaInst>(I))
InitialAllocaNum--;
assert(InitialAllocaNum == 0 && "We must not introduce any extra allocas");
#endif
}
/// Implement a unique function which doesn't require we sort the input
/// vector. Doing so has the effect of changing the output of a couple of
/// tests in ways which make them less useful in testing fused safepoints.
template <typename T> static void unique_unsorted(SmallVectorImpl<T> &Vec) {
SmallSet<T, 8> Seen;
Vec.erase(remove_if(Vec, [&](const T &V) { return !Seen.insert(V).second; }),
Vec.end());
}
/// Insert holders so that each Value is obviously live through the entire
/// lifetime of the call.
static void insertUseHolderAfter(CallSite &CS, const ArrayRef<Value *> Values,
SmallVectorImpl<CallInst *> &Holders) {
if (Values.empty())
// No values to hold live, might as well not insert the empty holder
return;
Module *M = CS.getInstruction()->getModule();
// Use a dummy vararg function to actually hold the values live
Function *Func = cast<Function>(M->getOrInsertFunction(
"__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true)));
if (CS.isCall()) {
// For call safepoints insert dummy calls right after safepoint
Holders.push_back(CallInst::Create(Func, Values, "",
&*++CS.getInstruction()->getIterator()));
return;
}
// For invoke safepooints insert dummy calls both in normal and
// exceptional destination blocks
auto *II = cast<InvokeInst>(CS.getInstruction());
Holders.push_back(CallInst::Create(
Func, Values, "", &*II->getNormalDest()->getFirstInsertionPt()));
Holders.push_back(CallInst::Create(
Func, Values, "", &*II->getUnwindDest()->getFirstInsertionPt()));
}
static void findLiveReferences(
Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate,
MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
GCPtrLivenessData OriginalLivenessData;
computeLiveInValues(DT, F, OriginalLivenessData);
for (size_t i = 0; i < records.size(); i++) {
struct PartiallyConstructedSafepointRecord &info = records[i];
analyzeParsePointLiveness(DT, OriginalLivenessData, toUpdate[i], info);
}
}
// Helper function for the "rematerializeLiveValues". It walks use chain
// starting from the "CurrentValue" until it reaches the root of the chain, i.e.
// the base or a value it cannot process. Only "simple" values are processed
// (currently it is GEP's and casts). The returned root is examined by the
// callers of findRematerializableChainToBasePointer. Fills "ChainToBase" array
// with all visited values.
static Value* findRematerializableChainToBasePointer(
SmallVectorImpl<Instruction*> &ChainToBase,
Value *CurrentValue) {
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurrentValue)) {
ChainToBase.push_back(GEP);
return findRematerializableChainToBasePointer(ChainToBase,
GEP->getPointerOperand());
}
if (CastInst *CI = dyn_cast<CastInst>(CurrentValue)) {
if (!CI->isNoopCast(CI->getModule()->getDataLayout()))
return CI;
ChainToBase.push_back(CI);
return findRematerializableChainToBasePointer(ChainToBase,
CI->getOperand(0));
}
// We have reached the root of the chain, which is either equal to the base or
// is the first unsupported value along the use chain.
return CurrentValue;
}
// Helper function for the "rematerializeLiveValues". Compute cost of the use
// chain we are going to rematerialize.
static unsigned
chainToBasePointerCost(SmallVectorImpl<Instruction*> &Chain,
TargetTransformInfo &TTI) {
unsigned Cost = 0;
for (Instruction *Instr : Chain) {
if (CastInst *CI = dyn_cast<CastInst>(Instr)) {
assert(CI->isNoopCast(CI->getModule()->getDataLayout()) &&
"non noop cast is found during rematerialization");
Type *SrcTy = CI->getOperand(0)->getType();
Cost += TTI.getCastInstrCost(CI->getOpcode(), CI->getType(), SrcTy, CI);
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Instr)) {
// Cost of the address calculation
Type *ValTy = GEP->getSourceElementType();
Cost += TTI.getAddressComputationCost(ValTy);
// And cost of the GEP itself
// TODO: Use TTI->getGEPCost here (it exists, but appears to be not
// allowed for the external usage)
if (!GEP->hasAllConstantIndices())
Cost += 2;
} else {
llvm_unreachable("unsupported instruction type during rematerialization");
}
}
return Cost;
}
static bool AreEquivalentPhiNodes(PHINode &OrigRootPhi, PHINode &AlternateRootPhi) {
unsigned PhiNum = OrigRootPhi.getNumIncomingValues();
if (PhiNum != AlternateRootPhi.getNumIncomingValues() ||
OrigRootPhi.getParent() != AlternateRootPhi.getParent())
return false;
// Map of incoming values and their corresponding basic blocks of
// OrigRootPhi.
SmallDenseMap<Value *, BasicBlock *, 8> CurrentIncomingValues;
for (unsigned i = 0; i < PhiNum; i++)
CurrentIncomingValues[OrigRootPhi.getIncomingValue(i)] =
OrigRootPhi.getIncomingBlock(i);
// Both current and base PHIs should have same incoming values and
// the same basic blocks corresponding to the incoming values.
for (unsigned i = 0; i < PhiNum; i++) {
auto CIVI =
CurrentIncomingValues.find(AlternateRootPhi.getIncomingValue(i));
if (CIVI == CurrentIncomingValues.end())
return false;
BasicBlock *CurrentIncomingBB = CIVI->second;
if (CurrentIncomingBB != AlternateRootPhi.getIncomingBlock(i))
return false;
}
return true;
}
// From the statepoint live set pick values that are cheaper to recompute then
// to relocate. Remove this values from the live set, rematerialize them after
// statepoint and record them in "Info" structure. Note that similar to
// relocated values we don't do any user adjustments here.
static void rematerializeLiveValues(CallSite CS,
PartiallyConstructedSafepointRecord &Info,
TargetTransformInfo &TTI) {
const unsigned int ChainLengthThreshold = 10;
// Record values we are going to delete from this statepoint live set.
// We can not di this in following loop due to iterator invalidation.
SmallVector<Value *, 32> LiveValuesToBeDeleted;
for (Value *LiveValue: Info.LiveSet) {
// For each live pointer find its defining chain
SmallVector<Instruction *, 3> ChainToBase;
assert(Info.PointerToBase.count(LiveValue));
Value *RootOfChain =
findRematerializableChainToBasePointer(ChainToBase,
LiveValue);
// Nothing to do, or chain is too long
if ( ChainToBase.size() == 0 ||
ChainToBase.size() > ChainLengthThreshold)
continue;
// Handle the scenario where the RootOfChain is not equal to the
// Base Value, but they are essentially the same phi values.
if (RootOfChain != Info.PointerToBase[LiveValue]) {
PHINode *OrigRootPhi = dyn_cast<PHINode>(RootOfChain);
PHINode *AlternateRootPhi = dyn_cast<PHINode>(Info.PointerToBase[LiveValue]);
if (!OrigRootPhi || !AlternateRootPhi)
continue;
// PHI nodes that have the same incoming values, and belonging to the same
// basic blocks are essentially the same SSA value. When the original phi
// has incoming values with different base pointers, the original phi is
// marked as conflict, and an additional `AlternateRootPhi` with the same
// incoming values get generated by the findBasePointer function. We need
// to identify the newly generated AlternateRootPhi (.base version of phi)
// and RootOfChain (the original phi node itself) are the same, so that we
// can rematerialize the gep and casts. This is a workaround for the
// deficiency in the findBasePointer algorithm.
if (!AreEquivalentPhiNodes(*OrigRootPhi, *AlternateRootPhi))
continue;
// Now that the phi nodes are proved to be the same, assert that
// findBasePointer's newly generated AlternateRootPhi is present in the
// liveset of the call.
assert(Info.LiveSet.count(AlternateRootPhi));
}
// Compute cost of this chain
unsigned Cost = chainToBasePointerCost(ChainToBase, TTI);
// TODO: We can also account for cases when we will be able to remove some
// of the rematerialized values by later optimization passes. I.e if
// we rematerialized several intersecting chains. Or if original values
// don't have any uses besides this statepoint.
// For invokes we need to rematerialize each chain twice - for normal and
// for unwind basic blocks. Model this by multiplying cost by two.
if (CS.isInvoke()) {
Cost *= 2;
}
// If it's too expensive - skip it
if (Cost >= RematerializationThreshold)
continue;
// Remove value from the live set
LiveValuesToBeDeleted.push_back(LiveValue);
// Clone instructions and record them inside "Info" structure
// Walk backwards to visit top-most instructions first
std::reverse(ChainToBase.begin(), ChainToBase.end());
// Utility function which clones all instructions from "ChainToBase"
// and inserts them before "InsertBefore". Returns rematerialized value
// which should be used after statepoint.
auto rematerializeChain = [&ChainToBase](
Instruction *InsertBefore, Value *RootOfChain, Value *AlternateLiveBase) {
Instruction *LastClonedValue = nullptr;
Instruction *LastValue = nullptr;
for (Instruction *Instr: ChainToBase) {
// Only GEP's and casts are supported as we need to be careful to not
// introduce any new uses of pointers not in the liveset.
// Note that it's fine to introduce new uses of pointers which were
// otherwise not used after this statepoint.
assert(isa<GetElementPtrInst>(Instr) || isa<CastInst>(Instr));
Instruction *ClonedValue = Instr->clone();
ClonedValue->insertBefore(InsertBefore);
ClonedValue->setName(Instr->getName() + ".remat");
// If it is not first instruction in the chain then it uses previously
// cloned value. We should update it to use cloned value.
if (LastClonedValue) {
assert(LastValue);
ClonedValue->replaceUsesOfWith(LastValue, LastClonedValue);
#ifndef NDEBUG
for (auto OpValue : ClonedValue->operand_values()) {
// Assert that cloned instruction does not use any instructions from
// this chain other than LastClonedValue
assert(!is_contained(ChainToBase, OpValue) &&
"incorrect use in rematerialization chain");
// Assert that the cloned instruction does not use the RootOfChain
// or the AlternateLiveBase.
assert(OpValue != RootOfChain && OpValue != AlternateLiveBase);
}
#endif
} else {
// For the first instruction, replace the use of unrelocated base i.e.
// RootOfChain/OrigRootPhi, with the corresponding PHI present in the
// live set. They have been proved to be the same PHI nodes. Note
// that the *only* use of the RootOfChain in the ChainToBase list is
// the first Value in the list.
if (RootOfChain != AlternateLiveBase)
ClonedValue->replaceUsesOfWith(RootOfChain, AlternateLiveBase);
}
LastClonedValue = ClonedValue;
LastValue = Instr;
}
assert(LastClonedValue);
return LastClonedValue;
};
// Different cases for calls and invokes. For invokes we need to clone
// instructions both on normal and unwind path.
if (CS.isCall()) {
Instruction *InsertBefore = CS.getInstruction()->getNextNode();
assert(InsertBefore);
Instruction *RematerializedValue = rematerializeChain(
InsertBefore, RootOfChain, Info.PointerToBase[LiveValue]);
Info.RematerializedValues[RematerializedValue] = LiveValue;
} else {
InvokeInst *Invoke = cast<InvokeInst>(CS.getInstruction());
Instruction *NormalInsertBefore =
&*Invoke->getNormalDest()->getFirstInsertionPt();
Instruction *UnwindInsertBefore =
&*Invoke->getUnwindDest()->getFirstInsertionPt();
Instruction *NormalRematerializedValue = rematerializeChain(
NormalInsertBefore, RootOfChain, Info.PointerToBase[LiveValue]);
Instruction *UnwindRematerializedValue = rematerializeChain(
UnwindInsertBefore, RootOfChain, Info.PointerToBase[LiveValue]);
Info.RematerializedValues[NormalRematerializedValue] = LiveValue;
Info.RematerializedValues[UnwindRematerializedValue] = LiveValue;
}
}
// Remove rematerializaed values from the live set
for (auto LiveValue: LiveValuesToBeDeleted) {
Info.LiveSet.remove(LiveValue);
}
}
static bool insertParsePoints(Function &F, DominatorTree &DT,
TargetTransformInfo &TTI,
SmallVectorImpl<CallSite> &ToUpdate) {
#ifndef NDEBUG
// sanity check the input
std::set<CallSite> Uniqued;
Uniqued.insert(ToUpdate.begin(), ToUpdate.end());
assert(Uniqued.size() == ToUpdate.size() && "no duplicates please!");
for (CallSite CS : ToUpdate)
assert(CS.getInstruction()->getFunction() == &F);
#endif
// When inserting gc.relocates for invokes, we need to be able to insert at
// the top of the successor blocks. See the comment on
// normalForInvokeSafepoint on exactly what is needed. Note that this step
// may restructure the CFG.
for (CallSite CS : ToUpdate) {
if (!CS.isInvoke())
continue;
auto *II = cast<InvokeInst>(CS.getInstruction());
normalizeForInvokeSafepoint(II->getNormalDest(), II->getParent(), DT);
normalizeForInvokeSafepoint(II->getUnwindDest(), II->getParent(), DT);
}
// A list of dummy calls added to the IR to keep various values obviously
// live in the IR. We'll remove all of these when done.
SmallVector<CallInst *, 64> Holders;
// Insert a dummy call with all of the deopt operands we'll need for the
// actual safepoint insertion as arguments. This ensures reference operands
// in the deopt argument list are considered live through the safepoint (and
// thus makes sure they get relocated.)
for (CallSite CS : ToUpdate) {
SmallVector<Value *, 64> DeoptValues;
for (Value *Arg : GetDeoptBundleOperands(CS)) {
assert(!isUnhandledGCPointerType(Arg->getType()) &&
"support for FCA unimplemented");
if (isHandledGCPointerType(Arg->getType()))
DeoptValues.push_back(Arg);
}
insertUseHolderAfter(CS, DeoptValues, Holders);
}
SmallVector<PartiallyConstructedSafepointRecord, 64> Records(ToUpdate.size());
// A) Identify all gc pointers which are statically live at the given call
// site.
findLiveReferences(F, DT, ToUpdate, Records);
// B) Find the base pointers for each live pointer
/* scope for caching */ {
// Cache the 'defining value' relation used in the computation and
// insertion of base phis and selects. This ensures that we don't insert
// large numbers of duplicate base_phis.
DefiningValueMapTy DVCache;
for (size_t i = 0; i < Records.size(); i++) {
PartiallyConstructedSafepointRecord &info = Records[i];
findBasePointers(DT, DVCache, ToUpdate[i], info);
}
} // end of cache scope
// The base phi insertion logic (for any safepoint) may have inserted new
// instructions which are now live at some safepoint. The simplest such
// example is:
// loop:
// phi a <-- will be a new base_phi here
// safepoint 1 <-- that needs to be live here
// gep a + 1
// safepoint 2
// br loop
// We insert some dummy calls after each safepoint to definitely hold live
// the base pointers which were identified for that safepoint. We'll then
// ask liveness for _every_ base inserted to see what is now live. Then we
// remove the dummy calls.
Holders.reserve(Holders.size() + Records.size());
for (size_t i = 0; i < Records.size(); i++) {
PartiallyConstructedSafepointRecord &Info = Records[i];
SmallVector<Value *, 128> Bases;
for (auto Pair : Info.PointerToBase)
Bases.push_back(Pair.second);
insertUseHolderAfter(ToUpdate[i], Bases, Holders);
}
// By selecting base pointers, we've effectively inserted new uses. Thus, we
// need to rerun liveness. We may *also* have inserted new defs, but that's
// not the key issue.
recomputeLiveInValues(F, DT, ToUpdate, Records);
if (PrintBasePointers) {
for (auto &Info : Records) {
errs() << "Base Pairs: (w/Relocation)\n";
for (auto Pair : Info.PointerToBase) {
errs() << " derived ";
Pair.first->printAsOperand(errs(), false);
errs() << " base ";
Pair.second->printAsOperand(errs(), false);
errs() << "\n";
}
}
}
// It is possible that non-constant live variables have a constant base. For
// example, a GEP with a variable offset from a global. In this case we can
// remove it from the liveset. We already don't add constants to the liveset
// because we assume they won't move at runtime and the GC doesn't need to be
// informed about them. The same reasoning applies if the base is constant.
// Note that the relocation placement code relies on this filtering for
// correctness as it expects the base to be in the liveset, which isn't true
// if the base is constant.
for (auto &Info : Records)
for (auto &BasePair : Info.PointerToBase)
if (isa<Constant>(BasePair.second))
Info.LiveSet.remove(BasePair.first);
for (CallInst *CI : Holders)
CI->eraseFromParent();
Holders.clear();
// In order to reduce live set of statepoint we might choose to rematerialize
// some values instead of relocating them. This is purely an optimization and
// does not influence correctness.
for (size_t i = 0; i < Records.size(); i++)
rematerializeLiveValues(ToUpdate[i], Records[i], TTI);
// We need this to safely RAUW and delete call or invoke return values that
// may themselves be live over a statepoint. For details, please see usage in
// makeStatepointExplicitImpl.
std::vector<DeferredReplacement> Replacements;
// Now run through and replace the existing statepoints with new ones with
// the live variables listed. We do not yet update uses of the values being
// relocated. We have references to live variables that need to
// survive to the last iteration of this loop. (By construction, the
// previous statepoint can not be a live variable, thus we can and remove
// the old statepoint calls as we go.)
for (size_t i = 0; i < Records.size(); i++)
makeStatepointExplicit(DT, ToUpdate[i], Records[i], Replacements);
ToUpdate.clear(); // prevent accident use of invalid CallSites
for (auto &PR : Replacements)
PR.doReplacement();
Replacements.clear();
for (auto &Info : Records) {
// These live sets may contain state Value pointers, since we replaced calls
// with operand bundles with calls wrapped in gc.statepoint, and some of
// those calls may have been def'ing live gc pointers. Clear these out to
// avoid accidentally using them.
//
// TODO: We should create a separate data structure that does not contain
// these live sets, and migrate to using that data structure from this point
// onward.
Info.LiveSet.clear();
Info.PointerToBase.clear();
}
// Do all the fixups of the original live variables to their relocated selves
SmallVector<Value *, 128> Live;
for (size_t i = 0; i < Records.size(); i++) {
PartiallyConstructedSafepointRecord &Info = Records[i];
// We can't simply save the live set from the original insertion. One of
// the live values might be the result of a call which needs a safepoint.
// That Value* no longer exists and we need to use the new gc_result.
// Thankfully, the live set is embedded in the statepoint (and updated), so
// we just grab that.
Statepoint Statepoint(Info.StatepointToken);
Live.insert(Live.end(), Statepoint.gc_args_begin(),
Statepoint.gc_args_end());
#ifndef NDEBUG
// Do some basic sanity checks on our liveness results before performing
// relocation. Relocation can and will turn mistakes in liveness results
// into non-sensical code which is must harder to debug.
// TODO: It would be nice to test consistency as well
assert(DT.isReachableFromEntry(Info.StatepointToken->getParent()) &&
"statepoint must be reachable or liveness is meaningless");
for (Value *V : Statepoint.gc_args()) {
if (!isa<Instruction>(V))
// Non-instruction values trivial dominate all possible uses
continue;
auto *LiveInst = cast<Instruction>(V);
assert(DT.isReachableFromEntry(LiveInst->getParent()) &&
"unreachable values should never be live");
assert(DT.dominates(LiveInst, Info.StatepointToken) &&
"basic SSA liveness expectation violated by liveness analysis");
}
#endif
}
unique_unsorted(Live);
#ifndef NDEBUG
// sanity check
for (auto *Ptr : Live)
assert(isHandledGCPointerType(Ptr->getType()) &&
"must be a gc pointer type");
#endif
relocationViaAlloca(F, DT, Live, Records);
return !Records.empty();
}
// Handles both return values and arguments for Functions and CallSites.
template <typename AttrHolder>
static void RemoveNonValidAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH,
unsigned Index) {
AttrBuilder R;
if (AH.getDereferenceableBytes(Index))
R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable,
AH.getDereferenceableBytes(Index)));
if (AH.getDereferenceableOrNullBytes(Index))
R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull,
AH.getDereferenceableOrNullBytes(Index)));
if (AH.getAttributes().hasAttribute(Index, Attribute::NoAlias))
R.addAttribute(Attribute::NoAlias);
if (!R.empty())
AH.setAttributes(AH.getAttributes().removeAttributes(Ctx, Index, R));
}
static void stripNonValidAttributesFromPrototype(Function &F) {
LLVMContext &Ctx = F.getContext();
for (Argument &A : F.args())
if (isa<PointerType>(A.getType()))
RemoveNonValidAttrAtIndex(Ctx, F,
A.getArgNo() + AttributeList::FirstArgIndex);
if (isa<PointerType>(F.getReturnType()))
RemoveNonValidAttrAtIndex(Ctx, F, AttributeList::ReturnIndex);
}
/// Certain metadata on instructions are invalid after running RS4GC.
/// Optimizations that run after RS4GC can incorrectly use this metadata to
/// optimize functions. We drop such metadata on the instruction.
static void stripInvalidMetadataFromInstruction(Instruction &I) {
if (!isa<LoadInst>(I) && !isa<StoreInst>(I))
return;
// These are the attributes that are still valid on loads and stores after
// RS4GC.
// The metadata implying dereferenceability and noalias are (conservatively)
// dropped. This is because semantically, after RewriteStatepointsForGC runs,
// all calls to gc.statepoint "free" the entire heap. Also, gc.statepoint can
// touch the entire heap including noalias objects. Note: The reasoning is
// same as stripping the dereferenceability and noalias attributes that are
// analogous to the metadata counterparts.
// We also drop the invariant.load metadata on the load because that metadata
// implies the address operand to the load points to memory that is never
// changed once it became dereferenceable. This is no longer true after RS4GC.
// Similar reasoning applies to invariant.group metadata, which applies to
// loads within a group.
unsigned ValidMetadataAfterRS4GC[] = {LLVMContext::MD_tbaa,
LLVMContext::MD_range,
LLVMContext::MD_alias_scope,
LLVMContext::MD_nontemporal,
LLVMContext::MD_nonnull,
LLVMContext::MD_align,
LLVMContext::MD_type};
// Drops all metadata on the instruction other than ValidMetadataAfterRS4GC.
I.dropUnknownNonDebugMetadata(ValidMetadataAfterRS4GC);
}
static void stripNonValidDataFromBody(Function &F) {
if (F.empty())
return;
LLVMContext &Ctx = F.getContext();
MDBuilder Builder(Ctx);
// Set of invariantstart instructions that we need to remove.
// Use this to avoid invalidating the instruction iterator.
SmallVector<IntrinsicInst*, 12> InvariantStartInstructions;
for (Instruction &I : instructions(F)) {
// invariant.start on memory location implies that the referenced memory
// location is constant and unchanging. This is no longer true after
// RewriteStatepointsForGC runs because there can be calls to gc.statepoint
// which frees the entire heap and the presence of invariant.start allows
// the optimizer to sink the load of a memory location past a statepoint,
// which is incorrect.
if (auto *II = dyn_cast<IntrinsicInst>(&I))
if (II->getIntrinsicID() == Intrinsic::invariant_start) {
InvariantStartInstructions.push_back(II);
continue;
}
if (MDNode *Tag = I.getMetadata(LLVMContext::MD_tbaa)) {
MDNode *MutableTBAA = Builder.createMutableTBAAAccessTag(Tag);
I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA);
}
stripInvalidMetadataFromInstruction(I);
if (CallSite CS = CallSite(&I)) {
for (int i = 0, e = CS.arg_size(); i != e; i++)
if (isa<PointerType>(CS.getArgument(i)->getType()))
RemoveNonValidAttrAtIndex(Ctx, CS, i + AttributeList::FirstArgIndex);
if (isa<PointerType>(CS.getType()))
RemoveNonValidAttrAtIndex(Ctx, CS, AttributeList::ReturnIndex);
}
}
// Delete the invariant.start instructions and RAUW undef.
for (auto *II : InvariantStartInstructions) {
II->replaceAllUsesWith(UndefValue::get(II->getType()));
II->eraseFromParent();
}
}
/// Returns true if this function should be rewritten by this pass. The main
/// point of this function is as an extension point for custom logic.
static bool shouldRewriteStatepointsIn(Function &F) {
// TODO: This should check the GCStrategy
if (F.hasGC()) {
const auto &FunctionGCName = F.getGC();
const StringRef StatepointExampleName("statepoint-example");
const StringRef CoreCLRName("coreclr");
return (StatepointExampleName == FunctionGCName) ||
(CoreCLRName == FunctionGCName);
} else
return false;
}
static void stripNonValidData(Module &M) {
#ifndef NDEBUG
assert(llvm::any_of(M, shouldRewriteStatepointsIn) && "precondition!");
#endif
for (Function &F : M)
stripNonValidAttributesFromPrototype(F);
for (Function &F : M)
stripNonValidDataFromBody(F);
}
bool RewriteStatepointsForGC::runOnFunction(Function &F, DominatorTree &DT,
TargetTransformInfo &TTI,
const TargetLibraryInfo &TLI) {
assert(!F.isDeclaration() && !F.empty() &&
"need function body to rewrite statepoints in");
assert(shouldRewriteStatepointsIn(F) && "mismatch in rewrite decision");
auto NeedsRewrite = [&TLI](Instruction &I) {
if (ImmutableCallSite CS = ImmutableCallSite(&I))
return !callsGCLeafFunction(CS, TLI) && !isStatepoint(CS);
return false;
};
// Delete any unreachable statepoints so that we don't have unrewritten
// statepoints surviving this pass. This makes testing easier and the
// resulting IR less confusing to human readers.
DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
bool MadeChange = removeUnreachableBlocks(F, nullptr, &DTU);
// Flush the Dominator Tree.
DTU.getDomTree();
// Gather all the statepoints which need rewritten. Be careful to only
// consider those in reachable code since we need to ask dominance queries
// when rewriting. We'll delete the unreachable ones in a moment.
SmallVector<CallSite, 64> ParsePointNeeded;
for (Instruction &I : instructions(F)) {
// TODO: only the ones with the flag set!
if (NeedsRewrite(I)) {
// NOTE removeUnreachableBlocks() is stronger than
// DominatorTree::isReachableFromEntry(). In other words
// removeUnreachableBlocks can remove some blocks for which
// isReachableFromEntry() returns true.
assert(DT.isReachableFromEntry(I.getParent()) &&
"no unreachable blocks expected");
ParsePointNeeded.push_back(CallSite(&I));
}
}
// Return early if no work to do.
if (ParsePointNeeded.empty())
return MadeChange;
// As a prepass, go ahead and aggressively destroy single entry phi nodes.
// These are created by LCSSA. They have the effect of increasing the size
// of liveness sets for no good reason. It may be harder to do this post
// insertion since relocations and base phis can confuse things.
for (BasicBlock &BB : F)
if (BB.getUniquePredecessor()) {
MadeChange = true;
FoldSingleEntryPHINodes(&BB);
}
// Before we start introducing relocations, we want to tweak the IR a bit to
// avoid unfortunate code generation effects. The main example is that we
// want to try to make sure the comparison feeding a branch is after any
// safepoints. Otherwise, we end up with a comparison of pre-relocation
// values feeding a branch after relocation. This is semantically correct,
// but results in extra register pressure since both the pre-relocation and
// post-relocation copies must be available in registers. For code without
// relocations this is handled elsewhere, but teaching the scheduler to
// reverse the transform we're about to do would be slightly complex.
// Note: This may extend the live range of the inputs to the icmp and thus
// increase the liveset of any statepoint we move over. This is profitable
// as long as all statepoints are in rare blocks. If we had in-register
// lowering for live values this would be a much safer transform.
auto getConditionInst = [](TerminatorInst *TI) -> Instruction* {
if (auto *BI = dyn_cast<BranchInst>(TI))
if (BI->isConditional())
return dyn_cast<Instruction>(BI->getCondition());
// TODO: Extend this to handle switches
return nullptr;
};
for (BasicBlock &BB : F) {
TerminatorInst *TI = BB.getTerminator();
if (auto *Cond = getConditionInst(TI))
// TODO: Handle more than just ICmps here. We should be able to move
// most instructions without side effects or memory access.
if (isa<ICmpInst>(Cond) && Cond->hasOneUse()) {
MadeChange = true;
Cond->moveBefore(TI);
}
}
MadeChange |= insertParsePoints(F, DT, TTI, ParsePointNeeded);
return MadeChange;
}
// liveness computation via standard dataflow
// -------------------------------------------------------------------
// TODO: Consider using bitvectors for liveness, the set of potentially
// interesting values should be small and easy to pre-compute.
/// Compute the live-in set for the location rbegin starting from
/// the live-out set of the basic block
static void computeLiveInValues(BasicBlock::reverse_iterator Begin,
BasicBlock::reverse_iterator End,
SetVector<Value *> &LiveTmp) {
for (auto &I : make_range(Begin, End)) {
// KILL/Def - Remove this definition from LiveIn
LiveTmp.remove(&I);
// Don't consider *uses* in PHI nodes, we handle their contribution to
// predecessor blocks when we seed the LiveOut sets
if (isa<PHINode>(I))
continue;
// USE - Add to the LiveIn set for this instruction
for (Value *V : I.operands()) {
assert(!isUnhandledGCPointerType(V->getType()) &&
"support for FCA unimplemented");
if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) {
// The choice to exclude all things constant here is slightly subtle.
// There are two independent reasons:
// - We assume that things which are constant (from LLVM's definition)
// do not move at runtime. For example, the address of a global
// variable is fixed, even though it's contents may not be.
// - Second, we can't disallow arbitrary inttoptr constants even
// if the language frontend does. Optimization passes are free to
// locally exploit facts without respect to global reachability. This
// can create sections of code which are dynamically unreachable and
// contain just about anything. (see constants.ll in tests)
LiveTmp.insert(V);
}
}
}
}
static void computeLiveOutSeed(BasicBlock *BB, SetVector<Value *> &LiveTmp) {
for (BasicBlock *Succ : successors(BB)) {
for (auto &I : *Succ) {
PHINode *PN = dyn_cast<PHINode>(&I);
if (!PN)
break;
Value *V = PN->getIncomingValueForBlock(BB);
assert(!isUnhandledGCPointerType(V->getType()) &&
"support for FCA unimplemented");
if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V))
LiveTmp.insert(V);
}
}
}
static SetVector<Value *> computeKillSet(BasicBlock *BB) {
SetVector<Value *> KillSet;
for (Instruction &I : *BB)
if (isHandledGCPointerType(I.getType()))
KillSet.insert(&I);
return KillSet;
}
#ifndef NDEBUG
/// Check that the items in 'Live' dominate 'TI'. This is used as a basic
/// sanity check for the liveness computation.
static void checkBasicSSA(DominatorTree &DT, SetVector<Value *> &Live,
TerminatorInst *TI, bool TermOkay = false) {
for (Value *V : Live) {
if (auto *I = dyn_cast<Instruction>(V)) {
// The terminator can be a member of the LiveOut set. LLVM's definition
// of instruction dominance states that V does not dominate itself. As
// such, we need to special case this to allow it.
if (TermOkay && TI == I)
continue;
assert(DT.dominates(I, TI) &&
"basic SSA liveness expectation violated by liveness analysis");
}
}
}
/// Check that all the liveness sets used during the computation of liveness
/// obey basic SSA properties. This is useful for finding cases where we miss
/// a def.
static void checkBasicSSA(DominatorTree &DT, GCPtrLivenessData &Data,
BasicBlock &BB) {
checkBasicSSA(DT, Data.LiveSet[&BB], BB.getTerminator());
checkBasicSSA(DT, Data.LiveOut[&BB], BB.getTerminator(), true);
checkBasicSSA(DT, Data.LiveIn[&BB], BB.getTerminator());
}
#endif
static void computeLiveInValues(DominatorTree &DT, Function &F,
GCPtrLivenessData &Data) {
SmallSetVector<BasicBlock *, 32> Worklist;
// Seed the liveness for each individual block
for (BasicBlock &BB : F) {
Data.KillSet[&BB] = computeKillSet(&BB);
Data.LiveSet[&BB].clear();
computeLiveInValues(BB.rbegin(), BB.rend(), Data.LiveSet[&BB]);
#ifndef NDEBUG
for (Value *Kill : Data.KillSet[&BB])
assert(!Data.LiveSet[&BB].count(Kill) && "live set contains kill");
#endif
Data.LiveOut[&BB] = SetVector<Value *>();
computeLiveOutSeed(&BB, Data.LiveOut[&BB]);
Data.LiveIn[&BB] = Data.LiveSet[&BB];
Data.LiveIn[&BB].set_union(Data.LiveOut[&BB]);
Data.LiveIn[&BB].set_subtract(Data.KillSet[&BB]);
if (!Data.LiveIn[&BB].empty())
Worklist.insert(pred_begin(&BB), pred_end(&BB));
}
// Propagate that liveness until stable
while (!Worklist.empty()) {
BasicBlock *BB = Worklist.pop_back_val();
// Compute our new liveout set, then exit early if it hasn't changed despite
// the contribution of our successor.
SetVector<Value *> LiveOut = Data.LiveOut[BB];
const auto OldLiveOutSize = LiveOut.size();
for (BasicBlock *Succ : successors(BB)) {
assert(Data.LiveIn.count(Succ));
LiveOut.set_union(Data.LiveIn[Succ]);
}
// assert OutLiveOut is a subset of LiveOut
if (OldLiveOutSize == LiveOut.size()) {
// If the sets are the same size, then we didn't actually add anything
// when unioning our successors LiveIn. Thus, the LiveIn of this block
// hasn't changed.
continue;
}
Data.LiveOut[BB] = LiveOut;
// Apply the effects of this basic block
SetVector<Value *> LiveTmp = LiveOut;
LiveTmp.set_union(Data.LiveSet[BB]);
LiveTmp.set_subtract(Data.KillSet[BB]);
assert(Data.LiveIn.count(BB));
const SetVector<Value *> &OldLiveIn = Data.LiveIn[BB];
// assert: OldLiveIn is a subset of LiveTmp
if (OldLiveIn.size() != LiveTmp.size()) {
Data.LiveIn[BB] = LiveTmp;
Worklist.insert(pred_begin(BB), pred_end(BB));
}
} // while (!Worklist.empty())
#ifndef NDEBUG
// Sanity check our output against SSA properties. This helps catch any
// missing kills during the above iteration.
for (BasicBlock &BB : F)
checkBasicSSA(DT, Data, BB);
#endif
}
static void findLiveSetAtInst(Instruction *Inst, GCPtrLivenessData &Data,
StatepointLiveSetTy &Out) {
BasicBlock *BB = Inst->getParent();
// Note: The copy is intentional and required
assert(Data.LiveOut.count(BB));
SetVector<Value *> LiveOut = Data.LiveOut[BB];
// We want to handle the statepoint itself oddly. It's
// call result is not live (normal), nor are it's arguments
// (unless they're used again later). This adjustment is
// specifically what we need to relocate
computeLiveInValues(BB->rbegin(), ++Inst->getIterator().getReverse(),
LiveOut);
LiveOut.remove(Inst);
Out.insert(LiveOut.begin(), LiveOut.end());
}
static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
CallSite CS,
PartiallyConstructedSafepointRecord &Info) {
Instruction *Inst = CS.getInstruction();
StatepointLiveSetTy Updated;
findLiveSetAtInst(Inst, RevisedLivenessData, Updated);
// We may have base pointers which are now live that weren't before. We need
// to update the PointerToBase structure to reflect this.
for (auto V : Updated)
if (Info.PointerToBase.insert({V, V}).second) {
assert(isKnownBaseResult(V) &&
"Can't find base for unexpected live value!");
continue;
}
#ifndef NDEBUG
for (auto V : Updated)
assert(Info.PointerToBase.count(V) &&
"Must be able to find base for live value!");
#endif
// Remove any stale base mappings - this can happen since our liveness is
// more precise then the one inherent in the base pointer analysis.
DenseSet<Value *> ToErase;
for (auto KVPair : Info.PointerToBase)
if (!Updated.count(KVPair.first))
ToErase.insert(KVPair.first);
for (auto *V : ToErase)
Info.PointerToBase.erase(V);
#ifndef NDEBUG
for (auto KVPair : Info.PointerToBase)
assert(Updated.count(KVPair.first) && "record for non-live value");
#endif
Info.LiveSet = Updated;
}
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