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llvm-mirror/lib/Transforms/Scalar/EarlyCSE.cpp
Kevin P. Neal d53eff6d30 [FPEnv] EarlyCSE support for constrained intrinsics, default FP environment edition 
EarlyCSE cannot distinguish between floating point instructions and
constrained floating point intrinsics that are marked as running in the
default FP environment. Said intrinsics are supposed to behave exactly the
same as the regular FP instructions. Teach EarlyCSE to handle them in that
case.

Differential Revision: https://reviews.llvm.org/D99962
2021-05-20 14:40:51 -04:00

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//===- EarlyCSE.cpp - Simple and fast CSE pass ----------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass performs a simple dominator tree walk that eliminates trivially
// redundant instructions.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/EarlyCSE.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopedHashTable.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/GuardUtils.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/Analysis/MemorySSAUpdater.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.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/PassManager.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/AtomicOrdering.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/DebugCounter.h"
#include "llvm/Support/RecyclingAllocator.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
#include "llvm/Transforms/Utils/GuardUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include <cassert>
#include <deque>
#include <memory>
#include <utility>
using namespace llvm;
using namespace llvm::PatternMatch;
#define DEBUG_TYPE "early-cse"
STATISTIC(NumSimplify, "Number of instructions simplified or DCE'd");
STATISTIC(NumCSE, "Number of instructions CSE'd");
STATISTIC(NumCSECVP, "Number of compare instructions CVP'd");
STATISTIC(NumCSELoad, "Number of load instructions CSE'd");
STATISTIC(NumCSECall, "Number of call instructions CSE'd");
STATISTIC(NumDSE, "Number of trivial dead stores removed");
DEBUG_COUNTER(CSECounter, "early-cse",
"Controls which instructions are removed");
static cl::opt<unsigned> EarlyCSEMssaOptCap(
"earlycse-mssa-optimization-cap", cl::init(500), cl::Hidden,
cl::desc("Enable imprecision in EarlyCSE in pathological cases, in exchange "
"for faster compile. Caps the MemorySSA clobbering calls."));
static cl::opt<bool> EarlyCSEDebugHash(
"earlycse-debug-hash", cl::init(false), cl::Hidden,
cl::desc("Perform extra assertion checking to verify that SimpleValue's hash "
"function is well-behaved w.r.t. its isEqual predicate"));
//===----------------------------------------------------------------------===//
// SimpleValue
//===----------------------------------------------------------------------===//
namespace {
/// Struct representing the available values in the scoped hash table.
struct SimpleValue {
Instruction *Inst;
SimpleValue(Instruction *I) : Inst(I) {
assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
}
bool isSentinel() const {
return Inst == DenseMapInfo<Instruction *>::getEmptyKey() ||
Inst == DenseMapInfo<Instruction *>::getTombstoneKey();
}
static bool canHandle(Instruction *Inst) {
// This can only handle non-void readnone functions.
// Also handled are constrained intrinsic that look like the types
// of instruction handled below (UnaryOperator, etc.).
if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
if (Function *F = CI->getCalledFunction()) {
switch ((Intrinsic::ID)F->getIntrinsicID()) {
case Intrinsic::experimental_constrained_fadd:
case Intrinsic::experimental_constrained_fsub:
case Intrinsic::experimental_constrained_fmul:
case Intrinsic::experimental_constrained_fdiv:
case Intrinsic::experimental_constrained_frem:
case Intrinsic::experimental_constrained_fptosi:
case Intrinsic::experimental_constrained_sitofp:
case Intrinsic::experimental_constrained_fptoui:
case Intrinsic::experimental_constrained_uitofp:
case Intrinsic::experimental_constrained_fcmp:
case Intrinsic::experimental_constrained_fcmps: {
auto *CFP = cast<ConstrainedFPIntrinsic>(CI);
return CFP->isDefaultFPEnvironment();
}
}
}
return CI->doesNotAccessMemory() && !CI->getType()->isVoidTy();
}
return isa<CastInst>(Inst) || isa<UnaryOperator>(Inst) ||
isa<BinaryOperator>(Inst) || isa<GetElementPtrInst>(Inst) ||
isa<CmpInst>(Inst) || isa<SelectInst>(Inst) ||
isa<ExtractElementInst>(Inst) || isa<InsertElementInst>(Inst) ||
isa<ShuffleVectorInst>(Inst) || isa<ExtractValueInst>(Inst) ||
isa<InsertValueInst>(Inst) || isa<FreezeInst>(Inst);
}
};
} // end anonymous namespace
namespace llvm {
template <> struct DenseMapInfo<SimpleValue> {
static inline SimpleValue getEmptyKey() {
return DenseMapInfo<Instruction *>::getEmptyKey();
}
static inline SimpleValue getTombstoneKey() {
return DenseMapInfo<Instruction *>::getTombstoneKey();
}
static unsigned getHashValue(SimpleValue Val);
static bool isEqual(SimpleValue LHS, SimpleValue RHS);
};
} // end namespace llvm
/// Match a 'select' including an optional 'not's of the condition.
static bool matchSelectWithOptionalNotCond(Value *V, Value *&Cond, Value *&A,
Value *&B,
SelectPatternFlavor &Flavor) {
// Return false if V is not even a select.
if (!match(V, m_Select(m_Value(Cond), m_Value(A), m_Value(B))))
return false;
// Look through a 'not' of the condition operand by swapping A/B.
Value *CondNot;
if (match(Cond, m_Not(m_Value(CondNot)))) {
Cond = CondNot;
std::swap(A, B);
}
// Match canonical forms of min/max. We are not using ValueTracking's
// more powerful matchSelectPattern() because it may rely on instruction flags
// such as "nsw". That would be incompatible with the current hashing
// mechanism that may remove flags to increase the likelihood of CSE.
Flavor = SPF_UNKNOWN;
CmpInst::Predicate Pred;
if (!match(Cond, m_ICmp(Pred, m_Specific(A), m_Specific(B)))) {
// Check for commuted variants of min/max by swapping predicate.
// If we do not match the standard or commuted patterns, this is not a
// recognized form of min/max, but it is still a select, so return true.
if (!match(Cond, m_ICmp(Pred, m_Specific(B), m_Specific(A))))
return true;
Pred = ICmpInst::getSwappedPredicate(Pred);
}
switch (Pred) {
case CmpInst::ICMP_UGT: Flavor = SPF_UMAX; break;
case CmpInst::ICMP_ULT: Flavor = SPF_UMIN; break;
case CmpInst::ICMP_SGT: Flavor = SPF_SMAX; break;
case CmpInst::ICMP_SLT: Flavor = SPF_SMIN; break;
// Non-strict inequalities.
case CmpInst::ICMP_ULE: Flavor = SPF_UMIN; break;
case CmpInst::ICMP_UGE: Flavor = SPF_UMAX; break;
case CmpInst::ICMP_SLE: Flavor = SPF_SMIN; break;
case CmpInst::ICMP_SGE: Flavor = SPF_SMAX; break;
default: break;
}
return true;
}
static unsigned getHashValueImpl(SimpleValue Val) {
Instruction *Inst = Val.Inst;
// Hash in all of the operands as pointers.
if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(Inst)) {
Value *LHS = BinOp->getOperand(0);
Value *RHS = BinOp->getOperand(1);
if (BinOp->isCommutative() && BinOp->getOperand(0) > BinOp->getOperand(1))
std::swap(LHS, RHS);
return hash_combine(BinOp->getOpcode(), LHS, RHS);
}
if (CmpInst *CI = dyn_cast<CmpInst>(Inst)) {
// Compares can be commuted by swapping the comparands and
// updating the predicate. Choose the form that has the
// comparands in sorted order, or in the case of a tie, the
// one with the lower predicate.
Value *LHS = CI->getOperand(0);
Value *RHS = CI->getOperand(1);
CmpInst::Predicate Pred = CI->getPredicate();
CmpInst::Predicate SwappedPred = CI->getSwappedPredicate();
if (std::tie(LHS, Pred) > std::tie(RHS, SwappedPred)) {
std::swap(LHS, RHS);
Pred = SwappedPred;
}
return hash_combine(Inst->getOpcode(), Pred, LHS, RHS);
}
// Hash general selects to allow matching commuted true/false operands.
SelectPatternFlavor SPF;
Value *Cond, *A, *B;
if (matchSelectWithOptionalNotCond(Inst, Cond, A, B, SPF)) {
// Hash min/max (cmp + select) to allow for commuted operands.
// Min/max may also have non-canonical compare predicate (eg, the compare for
// smin may use 'sgt' rather than 'slt'), and non-canonical operands in the
// compare.
// TODO: We should also detect FP min/max.
if (SPF == SPF_SMIN || SPF == SPF_SMAX ||
SPF == SPF_UMIN || SPF == SPF_UMAX) {
if (A > B)
std::swap(A, B);
return hash_combine(Inst->getOpcode(), SPF, A, B);
}
// Hash general selects to allow matching commuted true/false operands.
// If we do not have a compare as the condition, just hash in the condition.
CmpInst::Predicate Pred;
Value *X, *Y;
if (!match(Cond, m_Cmp(Pred, m_Value(X), m_Value(Y))))
return hash_combine(Inst->getOpcode(), Cond, A, B);
// Similar to cmp normalization (above) - canonicalize the predicate value:
// select (icmp Pred, X, Y), A, B --> select (icmp InvPred, X, Y), B, A
if (CmpInst::getInversePredicate(Pred) < Pred) {
Pred = CmpInst::getInversePredicate(Pred);
std::swap(A, B);
}
return hash_combine(Inst->getOpcode(), Pred, X, Y, A, B);
}
if (CastInst *CI = dyn_cast<CastInst>(Inst))
return hash_combine(CI->getOpcode(), CI->getType(), CI->getOperand(0));
if (FreezeInst *FI = dyn_cast<FreezeInst>(Inst))
return hash_combine(FI->getOpcode(), FI->getOperand(0));
if (const ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Inst))
return hash_combine(EVI->getOpcode(), EVI->getOperand(0),
hash_combine_range(EVI->idx_begin(), EVI->idx_end()));
if (const InsertValueInst *IVI = dyn_cast<InsertValueInst>(Inst))
return hash_combine(IVI->getOpcode(), IVI->getOperand(0),
IVI->getOperand(1),
hash_combine_range(IVI->idx_begin(), IVI->idx_end()));
assert((isa<CallInst>(Inst) || isa<GetElementPtrInst>(Inst) ||
isa<ExtractElementInst>(Inst) || isa<InsertElementInst>(Inst) ||
isa<ShuffleVectorInst>(Inst) || isa<UnaryOperator>(Inst) ||
isa<FreezeInst>(Inst)) &&
"Invalid/unknown instruction");
// Handle intrinsics with commutative operands.
// TODO: Extend this to handle intrinsics with >2 operands where the 1st
// 2 operands are commutative.
auto *II = dyn_cast<IntrinsicInst>(Inst);
if (II && II->isCommutative() && II->getNumArgOperands() == 2) {
Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
if (LHS > RHS)
std::swap(LHS, RHS);
return hash_combine(II->getOpcode(), LHS, RHS);
}
// gc.relocate is 'special' call: its second and third operands are
// not real values, but indices into statepoint's argument list.
// Get values they point to.
if (const GCRelocateInst *GCR = dyn_cast<GCRelocateInst>(Inst))
return hash_combine(GCR->getOpcode(), GCR->getOperand(0),
GCR->getBasePtr(), GCR->getDerivedPtr());
// Mix in the opcode.
return hash_combine(
Inst->getOpcode(),
hash_combine_range(Inst->value_op_begin(), Inst->value_op_end()));
}
unsigned DenseMapInfo<SimpleValue>::getHashValue(SimpleValue Val) {
#ifndef NDEBUG
// If -earlycse-debug-hash was specified, return a constant -- this
// will force all hashing to collide, so we'll exhaustively search
// the table for a match, and the assertion in isEqual will fire if
// there's a bug causing equal keys to hash differently.
if (EarlyCSEDebugHash)
return 0;
#endif
return getHashValueImpl(Val);
}
static bool isEqualImpl(SimpleValue LHS, SimpleValue RHS) {
Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
if (LHS.isSentinel() || RHS.isSentinel())
return LHSI == RHSI;
if (LHSI->getOpcode() != RHSI->getOpcode())
return false;
if (LHSI->isIdenticalToWhenDefined(RHSI))
return true;
// If we're not strictly identical, we still might be a commutable instruction
if (BinaryOperator *LHSBinOp = dyn_cast<BinaryOperator>(LHSI)) {
if (!LHSBinOp->isCommutative())
return false;
assert(isa<BinaryOperator>(RHSI) &&
"same opcode, but different instruction type?");
BinaryOperator *RHSBinOp = cast<BinaryOperator>(RHSI);
// Commuted equality
return LHSBinOp->getOperand(0) == RHSBinOp->getOperand(1) &&
LHSBinOp->getOperand(1) == RHSBinOp->getOperand(0);
}
if (CmpInst *LHSCmp = dyn_cast<CmpInst>(LHSI)) {
assert(isa<CmpInst>(RHSI) &&
"same opcode, but different instruction type?");
CmpInst *RHSCmp = cast<CmpInst>(RHSI);
// Commuted equality
return LHSCmp->getOperand(0) == RHSCmp->getOperand(1) &&
LHSCmp->getOperand(1) == RHSCmp->getOperand(0) &&
LHSCmp->getSwappedPredicate() == RHSCmp->getPredicate();
}
// TODO: Extend this for >2 args by matching the trailing N-2 args.
auto *LII = dyn_cast<IntrinsicInst>(LHSI);
auto *RII = dyn_cast<IntrinsicInst>(RHSI);
if (LII && RII && LII->getIntrinsicID() == RII->getIntrinsicID() &&
LII->isCommutative() && LII->getNumArgOperands() == 2) {
return LII->getArgOperand(0) == RII->getArgOperand(1) &&
LII->getArgOperand(1) == RII->getArgOperand(0);
}
// See comment above in `getHashValue()`.
if (const GCRelocateInst *GCR1 = dyn_cast<GCRelocateInst>(LHSI))
if (const GCRelocateInst *GCR2 = dyn_cast<GCRelocateInst>(RHSI))
return GCR1->getOperand(0) == GCR2->getOperand(0) &&
GCR1->getBasePtr() == GCR2->getBasePtr() &&
GCR1->getDerivedPtr() == GCR2->getDerivedPtr();
// Min/max can occur with commuted operands, non-canonical predicates,
// and/or non-canonical operands.
// Selects can be non-trivially equivalent via inverted conditions and swaps.
SelectPatternFlavor LSPF, RSPF;
Value *CondL, *CondR, *LHSA, *RHSA, *LHSB, *RHSB;
if (matchSelectWithOptionalNotCond(LHSI, CondL, LHSA, LHSB, LSPF) &&
matchSelectWithOptionalNotCond(RHSI, CondR, RHSA, RHSB, RSPF)) {
if (LSPF == RSPF) {
// TODO: We should also detect FP min/max.
if (LSPF == SPF_SMIN || LSPF == SPF_SMAX ||
LSPF == SPF_UMIN || LSPF == SPF_UMAX)
return ((LHSA == RHSA && LHSB == RHSB) ||
(LHSA == RHSB && LHSB == RHSA));
// select Cond, A, B <--> select not(Cond), B, A
if (CondL == CondR && LHSA == RHSA && LHSB == RHSB)
return true;
}
// If the true/false operands are swapped and the conditions are compares
// with inverted predicates, the selects are equal:
// select (icmp Pred, X, Y), A, B <--> select (icmp InvPred, X, Y), B, A
//
// This also handles patterns with a double-negation in the sense of not +
// inverse, because we looked through a 'not' in the matching function and
// swapped A/B:
// select (cmp Pred, X, Y), A, B <--> select (not (cmp InvPred, X, Y)), B, A
//
// This intentionally does NOT handle patterns with a double-negation in
// the sense of not + not, because doing so could result in values
// comparing
// as equal that hash differently in the min/max cases like:
// select (cmp slt, X, Y), X, Y <--> select (not (not (cmp slt, X, Y))), X, Y
// ^ hashes as min ^ would not hash as min
// In the context of the EarlyCSE pass, however, such cases never reach
// this code, as we simplify the double-negation before hashing the second
// select (and so still succeed at CSEing them).
if (LHSA == RHSB && LHSB == RHSA) {
CmpInst::Predicate PredL, PredR;
Value *X, *Y;
if (match(CondL, m_Cmp(PredL, m_Value(X), m_Value(Y))) &&
match(CondR, m_Cmp(PredR, m_Specific(X), m_Specific(Y))) &&
CmpInst::getInversePredicate(PredL) == PredR)
return true;
}
}
return false;
}
bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) {
// These comparisons are nontrivial, so assert that equality implies
// hash equality (DenseMap demands this as an invariant).
bool Result = isEqualImpl(LHS, RHS);
assert(!Result || (LHS.isSentinel() && LHS.Inst == RHS.Inst) ||
getHashValueImpl(LHS) == getHashValueImpl(RHS));
return Result;
}
//===----------------------------------------------------------------------===//
// CallValue
//===----------------------------------------------------------------------===//
namespace {
/// Struct representing the available call values in the scoped hash
/// table.
struct CallValue {
Instruction *Inst;
CallValue(Instruction *I) : Inst(I) {
assert((isSentinel() || canHandle(I)) && "Inst can't be handled!");
}
bool isSentinel() const {
return Inst == DenseMapInfo<Instruction *>::getEmptyKey() ||
Inst == DenseMapInfo<Instruction *>::getTombstoneKey();
}
static bool canHandle(Instruction *Inst) {
// Don't value number anything that returns void.
if (Inst->getType()->isVoidTy())
return false;
CallInst *CI = dyn_cast<CallInst>(Inst);
if (!CI || !CI->onlyReadsMemory())
return false;
return true;
}
};
} // end anonymous namespace
namespace llvm {
template <> struct DenseMapInfo<CallValue> {
static inline CallValue getEmptyKey() {
return DenseMapInfo<Instruction *>::getEmptyKey();
}
static inline CallValue getTombstoneKey() {
return DenseMapInfo<Instruction *>::getTombstoneKey();
}
static unsigned getHashValue(CallValue Val);
static bool isEqual(CallValue LHS, CallValue RHS);
};
} // end namespace llvm
unsigned DenseMapInfo<CallValue>::getHashValue(CallValue Val) {
Instruction *Inst = Val.Inst;
// Hash all of the operands as pointers and mix in the opcode.
return hash_combine(
Inst->getOpcode(),
hash_combine_range(Inst->value_op_begin(), Inst->value_op_end()));
}
bool DenseMapInfo<CallValue>::isEqual(CallValue LHS, CallValue RHS) {
Instruction *LHSI = LHS.Inst, *RHSI = RHS.Inst;
if (LHS.isSentinel() || RHS.isSentinel())
return LHSI == RHSI;
return LHSI->isIdenticalTo(RHSI);
}
//===----------------------------------------------------------------------===//
// EarlyCSE implementation
//===----------------------------------------------------------------------===//
namespace {
/// A simple and fast domtree-based CSE pass.
///
/// This pass does a simple depth-first walk over the dominator tree,
/// eliminating trivially redundant instructions and using instsimplify to
/// canonicalize things as it goes. It is intended to be fast and catch obvious
/// cases so that instcombine and other passes are more effective. It is
/// expected that a later pass of GVN will catch the interesting/hard cases.
class EarlyCSE {
public:
const TargetLibraryInfo &TLI;
const TargetTransformInfo &TTI;
DominatorTree &DT;
AssumptionCache &AC;
const SimplifyQuery SQ;
MemorySSA *MSSA;
std::unique_ptr<MemorySSAUpdater> MSSAUpdater;
using AllocatorTy =
RecyclingAllocator<BumpPtrAllocator,
ScopedHashTableVal<SimpleValue, Value *>>;
using ScopedHTType =
ScopedHashTable<SimpleValue, Value *, DenseMapInfo<SimpleValue>,
AllocatorTy>;
/// A scoped hash table of the current values of all of our simple
/// scalar expressions.
///
/// As we walk down the domtree, we look to see if instructions are in this:
/// if so, we replace them with what we find, otherwise we insert them so
/// that dominated values can succeed in their lookup.
ScopedHTType AvailableValues;
/// A scoped hash table of the current values of previously encountered
/// memory locations.
///
/// This allows us to get efficient access to dominating loads or stores when
/// we have a fully redundant load. In addition to the most recent load, we
/// keep track of a generation count of the read, which is compared against
/// the current generation count. The current generation count is incremented
/// after every possibly writing memory operation, which ensures that we only
/// CSE loads with other loads that have no intervening store. Ordering
/// events (such as fences or atomic instructions) increment the generation
/// count as well; essentially, we model these as writes to all possible
/// locations. Note that atomic and/or volatile loads and stores can be
/// present the table; it is the responsibility of the consumer to inspect
/// the atomicity/volatility if needed.
struct LoadValue {
Instruction *DefInst = nullptr;
unsigned Generation = 0;
int MatchingId = -1;
bool IsAtomic = false;
LoadValue() = default;
LoadValue(Instruction *Inst, unsigned Generation, unsigned MatchingId,
bool IsAtomic)
: DefInst(Inst), Generation(Generation), MatchingId(MatchingId),
IsAtomic(IsAtomic) {}
};
using LoadMapAllocator =
RecyclingAllocator<BumpPtrAllocator,
ScopedHashTableVal<Value *, LoadValue>>;
using LoadHTType =
ScopedHashTable<Value *, LoadValue, DenseMapInfo<Value *>,
LoadMapAllocator>;
LoadHTType AvailableLoads;
// A scoped hash table mapping memory locations (represented as typed
// addresses) to generation numbers at which that memory location became
// (henceforth indefinitely) invariant.
using InvariantMapAllocator =
RecyclingAllocator<BumpPtrAllocator,
ScopedHashTableVal<MemoryLocation, unsigned>>;
using InvariantHTType =
ScopedHashTable<MemoryLocation, unsigned, DenseMapInfo<MemoryLocation>,
InvariantMapAllocator>;
InvariantHTType AvailableInvariants;
/// A scoped hash table of the current values of read-only call
/// values.
///
/// It uses the same generation count as loads.
using CallHTType =
ScopedHashTable<CallValue, std::pair<Instruction *, unsigned>>;
CallHTType AvailableCalls;
/// This is the current generation of the memory value.
unsigned CurrentGeneration = 0;
/// Set up the EarlyCSE runner for a particular function.
EarlyCSE(const DataLayout &DL, const TargetLibraryInfo &TLI,
const TargetTransformInfo &TTI, DominatorTree &DT,
AssumptionCache &AC, MemorySSA *MSSA)
: TLI(TLI), TTI(TTI), DT(DT), AC(AC), SQ(DL, &TLI, &DT, &AC), MSSA(MSSA),
MSSAUpdater(std::make_unique<MemorySSAUpdater>(MSSA)) {}
bool run();
private:
unsigned ClobberCounter = 0;
// Almost a POD, but needs to call the constructors for the scoped hash
// tables so that a new scope gets pushed on. These are RAII so that the
// scope gets popped when the NodeScope is destroyed.
class NodeScope {
public:
NodeScope(ScopedHTType &AvailableValues, LoadHTType &AvailableLoads,
InvariantHTType &AvailableInvariants, CallHTType &AvailableCalls)
: Scope(AvailableValues), LoadScope(AvailableLoads),
InvariantScope(AvailableInvariants), CallScope(AvailableCalls) {}
NodeScope(const NodeScope &) = delete;
NodeScope &operator=(const NodeScope &) = delete;
private:
ScopedHTType::ScopeTy Scope;
LoadHTType::ScopeTy LoadScope;
InvariantHTType::ScopeTy InvariantScope;
CallHTType::ScopeTy CallScope;
};
// Contains all the needed information to create a stack for doing a depth
// first traversal of the tree. This includes scopes for values, loads, and
// calls as well as the generation. There is a child iterator so that the
// children do not need to be store separately.
class StackNode {
public:
StackNode(ScopedHTType &AvailableValues, LoadHTType &AvailableLoads,
InvariantHTType &AvailableInvariants, CallHTType &AvailableCalls,
unsigned cg, DomTreeNode *n, DomTreeNode::const_iterator child,
DomTreeNode::const_iterator end)
: CurrentGeneration(cg), ChildGeneration(cg), Node(n), ChildIter(child),
EndIter(end),
Scopes(AvailableValues, AvailableLoads, AvailableInvariants,
AvailableCalls)
{}
StackNode(const StackNode &) = delete;
StackNode &operator=(const StackNode &) = delete;
// Accessors.
unsigned currentGeneration() const { return CurrentGeneration; }
unsigned childGeneration() const { return ChildGeneration; }
void childGeneration(unsigned generation) { ChildGeneration = generation; }
DomTreeNode *node() { return Node; }
DomTreeNode::const_iterator childIter() const { return ChildIter; }
DomTreeNode *nextChild() {
DomTreeNode *child = *ChildIter;
++ChildIter;
return child;
}
DomTreeNode::const_iterator end() const { return EndIter; }
bool isProcessed() const { return Processed; }
void process() { Processed = true; }
private:
unsigned CurrentGeneration;
unsigned ChildGeneration;
DomTreeNode *Node;
DomTreeNode::const_iterator ChildIter;
DomTreeNode::const_iterator EndIter;
NodeScope Scopes;
bool Processed = false;
};
/// Wrapper class to handle memory instructions, including loads,
/// stores and intrinsic loads and stores defined by the target.
class ParseMemoryInst {
public:
ParseMemoryInst(Instruction *Inst, const TargetTransformInfo &TTI)
: Inst(Inst) {
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
IntrID = II->getIntrinsicID();
if (TTI.getTgtMemIntrinsic(II, Info))
return;
if (isHandledNonTargetIntrinsic(IntrID)) {
switch (IntrID) {
case Intrinsic::masked_load:
Info.PtrVal = Inst->getOperand(0);
Info.MatchingId = Intrinsic::masked_load;
Info.ReadMem = true;
Info.WriteMem = false;
Info.IsVolatile = false;
break;
case Intrinsic::masked_store:
Info.PtrVal = Inst->getOperand(1);
// Use the ID of masked load as the "matching id". This will
// prevent matching non-masked loads/stores with masked ones
// (which could be done), but at the moment, the code here
// does not support matching intrinsics with non-intrinsics,
// so keep the MatchingIds specific to masked instructions
// for now (TODO).
Info.MatchingId = Intrinsic::masked_load;
Info.ReadMem = false;
Info.WriteMem = true;
Info.IsVolatile = false;
break;
}
}
}
}
Instruction *get() { return Inst; }
const Instruction *get() const { return Inst; }
bool isLoad() const {
if (IntrID != 0)
return Info.ReadMem;
return isa<LoadInst>(Inst);
}
bool isStore() const {
if (IntrID != 0)
return Info.WriteMem;
return isa<StoreInst>(Inst);
}
bool isAtomic() const {
if (IntrID != 0)
return Info.Ordering != AtomicOrdering::NotAtomic;
return Inst->isAtomic();
}
bool isUnordered() const {
if (IntrID != 0)
return Info.isUnordered();
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
return LI->isUnordered();
} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
return SI->isUnordered();
}
// Conservative answer
return !Inst->isAtomic();
}
bool isVolatile() const {
if (IntrID != 0)
return Info.IsVolatile;
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
return LI->isVolatile();
} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
return SI->isVolatile();
}
// Conservative answer
return true;
}
bool isInvariantLoad() const {
if (auto *LI = dyn_cast<LoadInst>(Inst))
return LI->hasMetadata(LLVMContext::MD_invariant_load);
return false;
}
bool isValid() const { return getPointerOperand() != nullptr; }
// For regular (non-intrinsic) loads/stores, this is set to -1. For
// intrinsic loads/stores, the id is retrieved from the corresponding
// field in the MemIntrinsicInfo structure. That field contains
// non-negative values only.
int getMatchingId() const {
if (IntrID != 0)
return Info.MatchingId;
return -1;
}
Value *getPointerOperand() const {
if (IntrID != 0)
return Info.PtrVal;
return getLoadStorePointerOperand(Inst);
}
bool mayReadFromMemory() const {
if (IntrID != 0)
return Info.ReadMem;
return Inst->mayReadFromMemory();
}
bool mayWriteToMemory() const {
if (IntrID != 0)
return Info.WriteMem;
return Inst->mayWriteToMemory();
}
private:
Intrinsic::ID IntrID = 0;
MemIntrinsicInfo Info;
Instruction *Inst;
};
// This function is to prevent accidentally passing a non-target
// intrinsic ID to TargetTransformInfo.
static bool isHandledNonTargetIntrinsic(Intrinsic::ID ID) {
switch (ID) {
case Intrinsic::masked_load:
case Intrinsic::masked_store:
return true;
}
return false;
}
static bool isHandledNonTargetIntrinsic(const Value *V) {
if (auto *II = dyn_cast<IntrinsicInst>(V))
return isHandledNonTargetIntrinsic(II->getIntrinsicID());
return false;
}
bool processNode(DomTreeNode *Node);
bool handleBranchCondition(Instruction *CondInst, const BranchInst *BI,
const BasicBlock *BB, const BasicBlock *Pred);
Value *getMatchingValue(LoadValue &InVal, ParseMemoryInst &MemInst,
unsigned CurrentGeneration);
bool overridingStores(const ParseMemoryInst &Earlier,
const ParseMemoryInst &Later);
Value *getOrCreateResult(Value *Inst, Type *ExpectedType) const {
if (auto *LI = dyn_cast<LoadInst>(Inst))
return LI;
if (auto *SI = dyn_cast<StoreInst>(Inst))
return SI->getValueOperand();
assert(isa<IntrinsicInst>(Inst) && "Instruction not supported");
auto *II = cast<IntrinsicInst>(Inst);
if (isHandledNonTargetIntrinsic(II->getIntrinsicID()))
return getOrCreateResultNonTargetMemIntrinsic(II, ExpectedType);
return TTI.getOrCreateResultFromMemIntrinsic(II, ExpectedType);
}
Value *getOrCreateResultNonTargetMemIntrinsic(IntrinsicInst *II,
Type *ExpectedType) const {
switch (II->getIntrinsicID()) {
case Intrinsic::masked_load:
return II;
case Intrinsic::masked_store:
return II->getOperand(0);
}
return nullptr;
}
/// Return true if the instruction is known to only operate on memory
/// provably invariant in the given "generation".
bool isOperatingOnInvariantMemAt(Instruction *I, unsigned GenAt);
bool isSameMemGeneration(unsigned EarlierGeneration, unsigned LaterGeneration,
Instruction *EarlierInst, Instruction *LaterInst);
bool isNonTargetIntrinsicMatch(const IntrinsicInst *Earlier,
const IntrinsicInst *Later) {
auto IsSubmask = [](const Value *Mask0, const Value *Mask1) {
// Is Mask0 a submask of Mask1?
if (Mask0 == Mask1)
return true;
if (isa<UndefValue>(Mask0) || isa<UndefValue>(Mask1))
return false;
auto *Vec0 = dyn_cast<ConstantVector>(Mask0);
auto *Vec1 = dyn_cast<ConstantVector>(Mask1);
if (!Vec0 || !Vec1)
return false;
assert(Vec0->getType() == Vec1->getType() &&
"Masks should have the same type");
for (int i = 0, e = Vec0->getNumOperands(); i != e; ++i) {
Constant *Elem0 = Vec0->getOperand(i);
Constant *Elem1 = Vec1->getOperand(i);
auto *Int0 = dyn_cast<ConstantInt>(Elem0);
if (Int0 && Int0->isZero())
continue;
auto *Int1 = dyn_cast<ConstantInt>(Elem1);
if (Int1 && !Int1->isZero())
continue;
if (isa<UndefValue>(Elem0) || isa<UndefValue>(Elem1))
return false;
if (Elem0 == Elem1)
continue;
return false;
}
return true;
};
auto PtrOp = [](const IntrinsicInst *II) {
if (II->getIntrinsicID() == Intrinsic::masked_load)
return II->getOperand(0);
if (II->getIntrinsicID() == Intrinsic::masked_store)
return II->getOperand(1);
llvm_unreachable("Unexpected IntrinsicInst");
};
auto MaskOp = [](const IntrinsicInst *II) {
if (II->getIntrinsicID() == Intrinsic::masked_load)
return II->getOperand(2);
if (II->getIntrinsicID() == Intrinsic::masked_store)
return II->getOperand(3);
llvm_unreachable("Unexpected IntrinsicInst");
};
auto ThruOp = [](const IntrinsicInst *II) {
if (II->getIntrinsicID() == Intrinsic::masked_load)
return II->getOperand(3);
llvm_unreachable("Unexpected IntrinsicInst");
};
if (PtrOp(Earlier) != PtrOp(Later))
return false;
Intrinsic::ID IDE = Earlier->getIntrinsicID();
Intrinsic::ID IDL = Later->getIntrinsicID();
// We could really use specific intrinsic classes for masked loads
// and stores in IntrinsicInst.h.
if (IDE == Intrinsic::masked_load && IDL == Intrinsic::masked_load) {
// Trying to replace later masked load with the earlier one.
// Check that the pointers are the same, and
// - masks and pass-throughs are the same, or
// - replacee's pass-through is "undef" and replacer's mask is a
// super-set of the replacee's mask.
if (MaskOp(Earlier) == MaskOp(Later) && ThruOp(Earlier) == ThruOp(Later))
return true;
if (!isa<UndefValue>(ThruOp(Later)))
return false;
return IsSubmask(MaskOp(Later), MaskOp(Earlier));
}
if (IDE == Intrinsic::masked_store && IDL == Intrinsic::masked_load) {
// Trying to replace a load of a stored value with the store's value.
// Check that the pointers are the same, and
// - load's mask is a subset of store's mask, and
// - load's pass-through is "undef".
if (!IsSubmask(MaskOp(Later), MaskOp(Earlier)))
return false;
return isa<UndefValue>(ThruOp(Later));
}
if (IDE == Intrinsic::masked_load && IDL == Intrinsic::masked_store) {
// Trying to remove a store of the loaded value.
// Check that the pointers are the same, and
// - store's mask is a subset of the load's mask.
return IsSubmask(MaskOp(Later), MaskOp(Earlier));
}
if (IDE == Intrinsic::masked_store && IDL == Intrinsic::masked_store) {
// Trying to remove a dead store (earlier).
// Check that the pointers are the same,
// - the to-be-removed store's mask is a subset of the other store's
// mask.
return IsSubmask(MaskOp(Earlier), MaskOp(Later));
}
return false;
}
void removeMSSA(Instruction &Inst) {
if (!MSSA)
return;
if (VerifyMemorySSA)
MSSA->verifyMemorySSA();
// Removing a store here can leave MemorySSA in an unoptimized state by
// creating MemoryPhis that have identical arguments and by creating
// MemoryUses whose defining access is not an actual clobber. The phi case
// is handled by MemorySSA when passing OptimizePhis = true to
// removeMemoryAccess. The non-optimized MemoryUse case is lazily updated
// by MemorySSA's getClobberingMemoryAccess.
MSSAUpdater->removeMemoryAccess(&Inst, true);
}
};
} // end anonymous namespace
/// Determine if the memory referenced by LaterInst is from the same heap
/// version as EarlierInst.
/// This is currently called in two scenarios:
///
/// load p
/// ...
/// load p
///
/// and
///
/// x = load p
/// ...
/// store x, p
///
/// in both cases we want to verify that there are no possible writes to the
/// memory referenced by p between the earlier and later instruction.
bool EarlyCSE::isSameMemGeneration(unsigned EarlierGeneration,
unsigned LaterGeneration,
Instruction *EarlierInst,
Instruction *LaterInst) {
// Check the simple memory generation tracking first.
if (EarlierGeneration == LaterGeneration)
return true;
if (!MSSA)
return false;
// If MemorySSA has determined that one of EarlierInst or LaterInst does not
// read/write memory, then we can safely return true here.
// FIXME: We could be more aggressive when checking doesNotAccessMemory(),
// onlyReadsMemory(), mayReadFromMemory(), and mayWriteToMemory() in this pass
// by also checking the MemorySSA MemoryAccess on the instruction. Initial
// experiments suggest this isn't worthwhile, at least for C/C++ code compiled
// with the default optimization pipeline.
auto *EarlierMA = MSSA->getMemoryAccess(EarlierInst);
if (!EarlierMA)
return true;
auto *LaterMA = MSSA->getMemoryAccess(LaterInst);
if (!LaterMA)
return true;
// Since we know LaterDef dominates LaterInst and EarlierInst dominates
// LaterInst, if LaterDef dominates EarlierInst then it can't occur between
// EarlierInst and LaterInst and neither can any other write that potentially
// clobbers LaterInst.
MemoryAccess *LaterDef;
if (ClobberCounter < EarlyCSEMssaOptCap) {
LaterDef = MSSA->getWalker()->getClobberingMemoryAccess(LaterInst);
ClobberCounter++;
} else
LaterDef = LaterMA->getDefiningAccess();
return MSSA->dominates(LaterDef, EarlierMA);
}
bool EarlyCSE::isOperatingOnInvariantMemAt(Instruction *I, unsigned GenAt) {
// A location loaded from with an invariant_load is assumed to *never* change
// within the visible scope of the compilation.
if (auto *LI = dyn_cast<LoadInst>(I))
if (LI->hasMetadata(LLVMContext::MD_invariant_load))
return true;
auto MemLocOpt = MemoryLocation::getOrNone(I);
if (!MemLocOpt)
// "target" intrinsic forms of loads aren't currently known to
// MemoryLocation::get. TODO
return false;
MemoryLocation MemLoc = *MemLocOpt;
if (!AvailableInvariants.count(MemLoc))
return false;
// Is the generation at which this became invariant older than the
// current one?
return AvailableInvariants.lookup(MemLoc) <= GenAt;
}
bool EarlyCSE::handleBranchCondition(Instruction *CondInst,
const BranchInst *BI, const BasicBlock *BB,
const BasicBlock *Pred) {
assert(BI->isConditional() && "Should be a conditional branch!");
assert(BI->getCondition() == CondInst && "Wrong condition?");
assert(BI->getSuccessor(0) == BB || BI->getSuccessor(1) == BB);
auto *TorF = (BI->getSuccessor(0) == BB)
? ConstantInt::getTrue(BB->getContext())
: ConstantInt::getFalse(BB->getContext());
auto MatchBinOp = [](Instruction *I, unsigned Opcode, Value *&LHS,
Value *&RHS) {
if (Opcode == Instruction::And &&
match(I, m_LogicalAnd(m_Value(LHS), m_Value(RHS))))
return true;
else if (Opcode == Instruction::Or &&
match(I, m_LogicalOr(m_Value(LHS), m_Value(RHS))))
return true;
return false;
};
// If the condition is AND operation, we can propagate its operands into the
// true branch. If it is OR operation, we can propagate them into the false
// branch.
unsigned PropagateOpcode =
(BI->getSuccessor(0) == BB) ? Instruction::And : Instruction::Or;
bool MadeChanges = false;
SmallVector<Instruction *, 4> WorkList;
SmallPtrSet<Instruction *, 4> Visited;
WorkList.push_back(CondInst);
while (!WorkList.empty()) {
Instruction *Curr = WorkList.pop_back_val();
AvailableValues.insert(Curr, TorF);
LLVM_DEBUG(dbgs() << "EarlyCSE CVP: Add conditional value for '"
<< Curr->getName() << "' as " << *TorF << " in "
<< BB->getName() << "\n");
if (!DebugCounter::shouldExecute(CSECounter)) {
LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
} else {
// Replace all dominated uses with the known value.
if (unsigned Count = replaceDominatedUsesWith(Curr, TorF, DT,
BasicBlockEdge(Pred, BB))) {
NumCSECVP += Count;
MadeChanges = true;
}
}
Value *LHS, *RHS;
if (MatchBinOp(Curr, PropagateOpcode, LHS, RHS))
for (auto &Op : { LHS, RHS })
if (Instruction *OPI = dyn_cast<Instruction>(Op))
if (SimpleValue::canHandle(OPI) && Visited.insert(OPI).second)
WorkList.push_back(OPI);
}
return MadeChanges;
}
Value *EarlyCSE::getMatchingValue(LoadValue &InVal, ParseMemoryInst &MemInst,
unsigned CurrentGeneration) {
if (InVal.DefInst == nullptr)
return nullptr;
if (InVal.MatchingId != MemInst.getMatchingId())
return nullptr;
// We don't yet handle removing loads with ordering of any kind.
if (MemInst.isVolatile() || !MemInst.isUnordered())
return nullptr;
// We can't replace an atomic load with one which isn't also atomic.
if (MemInst.isLoad() && !InVal.IsAtomic && MemInst.isAtomic())
return nullptr;
// The value V returned from this function is used differently depending
// on whether MemInst is a load or a store. If it's a load, we will replace
// MemInst with V, if it's a store, we will check if V is the same as the
// available value.
bool MemInstMatching = !MemInst.isLoad();
Instruction *Matching = MemInstMatching ? MemInst.get() : InVal.DefInst;
Instruction *Other = MemInstMatching ? InVal.DefInst : MemInst.get();
// For stores check the result values before checking memory generation
// (otherwise isSameMemGeneration may crash).
Value *Result = MemInst.isStore()
? getOrCreateResult(Matching, Other->getType())
: nullptr;
if (MemInst.isStore() && InVal.DefInst != Result)
return nullptr;
// Deal with non-target memory intrinsics.
bool MatchingNTI = isHandledNonTargetIntrinsic(Matching);
bool OtherNTI = isHandledNonTargetIntrinsic(Other);
if (OtherNTI != MatchingNTI)
return nullptr;
if (OtherNTI && MatchingNTI) {
if (!isNonTargetIntrinsicMatch(cast<IntrinsicInst>(InVal.DefInst),
cast<IntrinsicInst>(MemInst.get())))
return nullptr;
}
if (!isOperatingOnInvariantMemAt(MemInst.get(), InVal.Generation) &&
!isSameMemGeneration(InVal.Generation, CurrentGeneration, InVal.DefInst,
MemInst.get()))
return nullptr;
if (!Result)
Result = getOrCreateResult(Matching, Other->getType());
return Result;
}
bool EarlyCSE::overridingStores(const ParseMemoryInst &Earlier,
const ParseMemoryInst &Later) {
// Can we remove Earlier store because of Later store?
assert(Earlier.isUnordered() && !Earlier.isVolatile() &&
"Violated invariant");
if (Earlier.getPointerOperand() != Later.getPointerOperand())
return false;
if (Earlier.getMatchingId() != Later.getMatchingId())
return false;
// At the moment, we don't remove ordered stores, but do remove
// unordered atomic stores. There's no special requirement (for
// unordered atomics) about removing atomic stores only in favor of
// other atomic stores since we were going to execute the non-atomic
// one anyway and the atomic one might never have become visible.
if (!Earlier.isUnordered() || !Later.isUnordered())
return false;
// Deal with non-target memory intrinsics.
bool ENTI = isHandledNonTargetIntrinsic(Earlier.get());
bool LNTI = isHandledNonTargetIntrinsic(Later.get());
if (ENTI && LNTI)
return isNonTargetIntrinsicMatch(cast<IntrinsicInst>(Earlier.get()),
cast<IntrinsicInst>(Later.get()));
// Because of the check above, at least one of them is false.
// For now disallow matching intrinsics with non-intrinsics,
// so assume that the stores match if neither is an intrinsic.
return ENTI == LNTI;
}
bool EarlyCSE::processNode(DomTreeNode *Node) {
bool Changed = false;
BasicBlock *BB = Node->getBlock();
// If this block has a single predecessor, then the predecessor is the parent
// of the domtree node and all of the live out memory values are still current
// in this block. If this block has multiple predecessors, then they could
// have invalidated the live-out memory values of our parent value. For now,
// just be conservative and invalidate memory if this block has multiple
// predecessors.
if (!BB->getSinglePredecessor())
++CurrentGeneration;
// If this node has a single predecessor which ends in a conditional branch,
// we can infer the value of the branch condition given that we took this
// path. We need the single predecessor to ensure there's not another path
// which reaches this block where the condition might hold a different
// value. Since we're adding this to the scoped hash table (like any other
// def), it will have been popped if we encounter a future merge block.
if (BasicBlock *Pred = BB->getSinglePredecessor()) {
auto *BI = dyn_cast<BranchInst>(Pred->getTerminator());
if (BI && BI->isConditional()) {
auto *CondInst = dyn_cast<Instruction>(BI->getCondition());
if (CondInst && SimpleValue::canHandle(CondInst))
Changed |= handleBranchCondition(CondInst, BI, BB, Pred);
}
}
/// LastStore - Keep track of the last non-volatile store that we saw... for
/// as long as there in no instruction that reads memory. If we see a store
/// to the same location, we delete the dead store. This zaps trivial dead
/// stores which can occur in bitfield code among other things.
Instruction *LastStore = nullptr;
// See if any instructions in the block can be eliminated. If so, do it. If
// not, add them to AvailableValues.
for (Instruction &Inst : make_early_inc_range(BB->getInstList())) {
// Dead instructions should just be removed.
if (isInstructionTriviallyDead(&Inst, &TLI)) {
LLVM_DEBUG(dbgs() << "EarlyCSE DCE: " << Inst << '\n');
if (!DebugCounter::shouldExecute(CSECounter)) {
LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
continue;
}
salvageKnowledge(&Inst, &AC);
salvageDebugInfo(Inst);
removeMSSA(Inst);
Inst.eraseFromParent();
Changed = true;
++NumSimplify;
continue;
}
// Skip assume intrinsics, they don't really have side effects (although
// they're marked as such to ensure preservation of control dependencies),
// and this pass will not bother with its removal. However, we should mark
// its condition as true for all dominated blocks.
if (auto *Assume = dyn_cast<AssumeInst>(&Inst)) {
auto *CondI = dyn_cast<Instruction>(Assume->getArgOperand(0));
if (CondI && SimpleValue::canHandle(CondI)) {
LLVM_DEBUG(dbgs() << "EarlyCSE considering assumption: " << Inst
<< '\n');
AvailableValues.insert(CondI, ConstantInt::getTrue(BB->getContext()));
} else
LLVM_DEBUG(dbgs() << "EarlyCSE skipping assumption: " << Inst << '\n');
continue;
}
// Likewise, noalias intrinsics don't actually write.
if (match(&Inst,
m_Intrinsic<Intrinsic::experimental_noalias_scope_decl>())) {
LLVM_DEBUG(dbgs() << "EarlyCSE skipping noalias intrinsic: " << Inst
<< '\n');
continue;
}
// Skip sideeffect intrinsics, for the same reason as assume intrinsics.
if (match(&Inst, m_Intrinsic<Intrinsic::sideeffect>())) {
LLVM_DEBUG(dbgs() << "EarlyCSE skipping sideeffect: " << Inst << '\n');
continue;
}
// We can skip all invariant.start intrinsics since they only read memory,
// and we can forward values across it. For invariant starts without
// invariant ends, we can use the fact that the invariantness never ends to
// start a scope in the current generaton which is true for all future
// generations. Also, we dont need to consume the last store since the
// semantics of invariant.start allow us to perform DSE of the last
// store, if there was a store following invariant.start. Consider:
//
// store 30, i8* p
// invariant.start(p)
// store 40, i8* p
// We can DSE the store to 30, since the store 40 to invariant location p
// causes undefined behaviour.
if (match(&Inst, m_Intrinsic<Intrinsic::invariant_start>())) {
// If there are any uses, the scope might end.
if (!Inst.use_empty())
continue;
MemoryLocation MemLoc =
MemoryLocation::getForArgument(&cast<CallInst>(Inst), 1, TLI);
// Don't start a scope if we already have a better one pushed
if (!AvailableInvariants.count(MemLoc))
AvailableInvariants.insert(MemLoc, CurrentGeneration);
continue;
}
if (isGuard(&Inst)) {
if (auto *CondI =
dyn_cast<Instruction>(cast<CallInst>(Inst).getArgOperand(0))) {
if (SimpleValue::canHandle(CondI)) {
// Do we already know the actual value of this condition?
if (auto *KnownCond = AvailableValues.lookup(CondI)) {
// Is the condition known to be true?
if (isa<ConstantInt>(KnownCond) &&
cast<ConstantInt>(KnownCond)->isOne()) {
LLVM_DEBUG(dbgs()
<< "EarlyCSE removing guard: " << Inst << '\n');
salvageKnowledge(&Inst, &AC);
removeMSSA(Inst);
Inst.eraseFromParent();
Changed = true;
continue;
} else
// Use the known value if it wasn't true.
cast<CallInst>(Inst).setArgOperand(0, KnownCond);
}
// The condition we're on guarding here is true for all dominated
// locations.
AvailableValues.insert(CondI, ConstantInt::getTrue(BB->getContext()));
}
}
// Guard intrinsics read all memory, but don't write any memory.
// Accordingly, don't update the generation but consume the last store (to
// avoid an incorrect DSE).
LastStore = nullptr;
continue;
}
// If the instruction can be simplified (e.g. X+0 = X) then replace it with
// its simpler value.
if (Value *V = SimplifyInstruction(&Inst, SQ)) {
LLVM_DEBUG(dbgs() << "EarlyCSE Simplify: " << Inst << " to: " << *V
<< '\n');
if (!DebugCounter::shouldExecute(CSECounter)) {
LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
} else {
bool Killed = false;
if (!Inst.use_empty()) {
Inst.replaceAllUsesWith(V);
Changed = true;
}
if (isInstructionTriviallyDead(&Inst, &TLI)) {
salvageKnowledge(&Inst, &AC);
removeMSSA(Inst);
Inst.eraseFromParent();
Changed = true;
Killed = true;
}
if (Changed)
++NumSimplify;
if (Killed)
continue;
}
}
// If this is a simple instruction that we can value number, process it.
if (SimpleValue::canHandle(&Inst)) {
// See if the instruction has an available value. If so, use it.
if (Value *V = AvailableValues.lookup(&Inst)) {
LLVM_DEBUG(dbgs() << "EarlyCSE CSE: " << Inst << " to: " << *V
<< '\n');
if (!DebugCounter::shouldExecute(CSECounter)) {
LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
continue;
}
if (auto *I = dyn_cast<Instruction>(V))
I->andIRFlags(&Inst);
Inst.replaceAllUsesWith(V);
salvageKnowledge(&Inst, &AC);
removeMSSA(Inst);
Inst.eraseFromParent();
Changed = true;
++NumCSE;
continue;
}
// Otherwise, just remember that this value is available.
AvailableValues.insert(&Inst, &Inst);
continue;
}
ParseMemoryInst MemInst(&Inst, TTI);
// If this is a non-volatile load, process it.
if (MemInst.isValid() && MemInst.isLoad()) {
// (conservatively) we can't peak past the ordering implied by this
// operation, but we can add this load to our set of available values
if (MemInst.isVolatile() || !MemInst.isUnordered()) {
LastStore = nullptr;
++CurrentGeneration;
}
if (MemInst.isInvariantLoad()) {
// If we pass an invariant load, we know that memory location is
// indefinitely constant from the moment of first dereferenceability.
// We conservatively treat the invariant_load as that moment. If we
// pass a invariant load after already establishing a scope, don't
// restart it since we want to preserve the earliest point seen.
auto MemLoc = MemoryLocation::get(&Inst);
if (!AvailableInvariants.count(MemLoc))
AvailableInvariants.insert(MemLoc, CurrentGeneration);
}
// If we have an available version of this load, and if it is the right
// generation or the load is known to be from an invariant location,
// replace this instruction.
//
// If either the dominating load or the current load are invariant, then
// we can assume the current load loads the same value as the dominating
// load.
LoadValue InVal = AvailableLoads.lookup(MemInst.getPointerOperand());
if (Value *Op = getMatchingValue(InVal, MemInst, CurrentGeneration)) {
LLVM_DEBUG(dbgs() << "EarlyCSE CSE LOAD: " << Inst
<< " to: " << *InVal.DefInst << '\n');
if (!DebugCounter::shouldExecute(CSECounter)) {
LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
continue;
}
if (!Inst.use_empty())
Inst.replaceAllUsesWith(Op);
salvageKnowledge(&Inst, &AC);
removeMSSA(Inst);
Inst.eraseFromParent();
Changed = true;
++NumCSELoad;
continue;
}
// Otherwise, remember that we have this instruction.
AvailableLoads.insert(MemInst.getPointerOperand(),
LoadValue(&Inst, CurrentGeneration,
MemInst.getMatchingId(),
MemInst.isAtomic()));
LastStore = nullptr;
continue;
}
// If this instruction may read from memory or throw (and potentially read
// from memory in the exception handler), forget LastStore. Load/store
// intrinsics will indicate both a read and a write to memory. The target
// may override this (e.g. so that a store intrinsic does not read from
// memory, and thus will be treated the same as a regular store for
// commoning purposes).
if ((Inst.mayReadFromMemory() || Inst.mayThrow()) &&
!(MemInst.isValid() && !MemInst.mayReadFromMemory()))
LastStore = nullptr;
// If this is a read-only call, process it.
if (CallValue::canHandle(&Inst)) {
// If we have an available version of this call, and if it is the right
// generation, replace this instruction.
std::pair<Instruction *, unsigned> InVal = AvailableCalls.lookup(&Inst);
if (InVal.first != nullptr &&
isSameMemGeneration(InVal.second, CurrentGeneration, InVal.first,
&Inst)) {
LLVM_DEBUG(dbgs() << "EarlyCSE CSE CALL: " << Inst
<< " to: " << *InVal.first << '\n');
if (!DebugCounter::shouldExecute(CSECounter)) {
LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
continue;
}
if (!Inst.use_empty())
Inst.replaceAllUsesWith(InVal.first);
salvageKnowledge(&Inst, &AC);
removeMSSA(Inst);
Inst.eraseFromParent();
Changed = true;
++NumCSECall;
continue;
}
// Otherwise, remember that we have this instruction.
AvailableCalls.insert(&Inst, std::make_pair(&Inst, CurrentGeneration));
continue;
}
// A release fence requires that all stores complete before it, but does
// not prevent the reordering of following loads 'before' the fence. As a
// result, we don't need to consider it as writing to memory and don't need
// to advance the generation. We do need to prevent DSE across the fence,
// but that's handled above.
if (auto *FI = dyn_cast<FenceInst>(&Inst))
if (FI->getOrdering() == AtomicOrdering::Release) {
assert(Inst.mayReadFromMemory() && "relied on to prevent DSE above");
continue;
}
// write back DSE - If we write back the same value we just loaded from
// the same location and haven't passed any intervening writes or ordering
// operations, we can remove the write. The primary benefit is in allowing
// the available load table to remain valid and value forward past where
// the store originally was.
if (MemInst.isValid() && MemInst.isStore()) {
LoadValue InVal = AvailableLoads.lookup(MemInst.getPointerOperand());
if (InVal.DefInst &&
InVal.DefInst == getMatchingValue(InVal, MemInst, CurrentGeneration)) {
// It is okay to have a LastStore to a different pointer here if MemorySSA
// tells us that the load and store are from the same memory generation.
// In that case, LastStore should keep its present value since we're
// removing the current store.
assert((!LastStore ||
ParseMemoryInst(LastStore, TTI).getPointerOperand() ==
MemInst.getPointerOperand() ||
MSSA) &&
"can't have an intervening store if not using MemorySSA!");
LLVM_DEBUG(dbgs() << "EarlyCSE DSE (writeback): " << Inst << '\n');
if (!DebugCounter::shouldExecute(CSECounter)) {
LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
continue;
}
salvageKnowledge(&Inst, &AC);
removeMSSA(Inst);
Inst.eraseFromParent();
Changed = true;
++NumDSE;
// We can avoid incrementing the generation count since we were able
// to eliminate this store.
continue;
}
}
// Okay, this isn't something we can CSE at all. Check to see if it is
// something that could modify memory. If so, our available memory values
// cannot be used so bump the generation count.
if (Inst.mayWriteToMemory()) {
++CurrentGeneration;
if (MemInst.isValid() && MemInst.isStore()) {
// We do a trivial form of DSE if there are two stores to the same
// location with no intervening loads. Delete the earlier store.
if (LastStore) {
if (overridingStores(ParseMemoryInst(LastStore, TTI), MemInst)) {
LLVM_DEBUG(dbgs() << "EarlyCSE DEAD STORE: " << *LastStore
<< " due to: " << Inst << '\n');
if (!DebugCounter::shouldExecute(CSECounter)) {
LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
} else {
salvageKnowledge(&Inst, &AC);
removeMSSA(*LastStore);
LastStore->eraseFromParent();
Changed = true;
++NumDSE;
LastStore = nullptr;
}
}
// fallthrough - we can exploit information about this store
}
// Okay, we just invalidated anything we knew about loaded values. Try
// to salvage *something* by remembering that the stored value is a live
// version of the pointer. It is safe to forward from volatile stores
// to non-volatile loads, so we don't have to check for volatility of
// the store.
AvailableLoads.insert(MemInst.getPointerOperand(),
LoadValue(&Inst, CurrentGeneration,
MemInst.getMatchingId(),
MemInst.isAtomic()));
// Remember that this was the last unordered store we saw for DSE. We
// don't yet handle DSE on ordered or volatile stores since we don't
// have a good way to model the ordering requirement for following
// passes once the store is removed. We could insert a fence, but
// since fences are slightly stronger than stores in their ordering,
// it's not clear this is a profitable transform. Another option would
// be to merge the ordering with that of the post dominating store.
if (MemInst.isUnordered() && !MemInst.isVolatile())
LastStore = &Inst;
else
LastStore = nullptr;
}
}
}
return Changed;
}
bool EarlyCSE::run() {
// Note, deque is being used here because there is significant performance
// gains over vector when the container becomes very large due to the
// specific access patterns. For more information see the mailing list
// discussion on this:
// http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20120116/135228.html
std::deque<StackNode *> nodesToProcess;
bool Changed = false;
// Process the root node.
nodesToProcess.push_back(new StackNode(
AvailableValues, AvailableLoads, AvailableInvariants, AvailableCalls,
CurrentGeneration, DT.getRootNode(),
DT.getRootNode()->begin(), DT.getRootNode()->end()));
assert(!CurrentGeneration && "Create a new EarlyCSE instance to rerun it.");
// Process the stack.
while (!nodesToProcess.empty()) {
// Grab the first item off the stack. Set the current generation, remove
// the node from the stack, and process it.
StackNode *NodeToProcess = nodesToProcess.back();
// Initialize class members.
CurrentGeneration = NodeToProcess->currentGeneration();
// Check if the node needs to be processed.
if (!NodeToProcess->isProcessed()) {
// Process the node.
Changed |= processNode(NodeToProcess->node());
NodeToProcess->childGeneration(CurrentGeneration);
NodeToProcess->process();
} else if (NodeToProcess->childIter() != NodeToProcess->end()) {
// Push the next child onto the stack.
DomTreeNode *child = NodeToProcess->nextChild();
nodesToProcess.push_back(
new StackNode(AvailableValues, AvailableLoads, AvailableInvariants,
AvailableCalls, NodeToProcess->childGeneration(),
child, child->begin(), child->end()));
} else {
// It has been processed, and there are no more children to process,
// so delete it and pop it off the stack.
delete NodeToProcess;
nodesToProcess.pop_back();
}
} // while (!nodes...)
return Changed;
}
PreservedAnalyses EarlyCSEPass::run(Function &F,
FunctionAnalysisManager &AM) {
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &TTI = AM.getResult<TargetIRAnalysis>(F);
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
auto &AC = AM.getResult<AssumptionAnalysis>(F);
auto *MSSA =
UseMemorySSA ? &AM.getResult<MemorySSAAnalysis>(F).getMSSA() : nullptr;
EarlyCSE CSE(F.getParent()->getDataLayout(), TLI, TTI, DT, AC, MSSA);
if (!CSE.run())
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
if (UseMemorySSA)
PA.preserve<MemorySSAAnalysis>();
return PA;
}
namespace {
/// A simple and fast domtree-based CSE pass.
///
/// This pass does a simple depth-first walk over the dominator tree,
/// eliminating trivially redundant instructions and using instsimplify to
/// canonicalize things as it goes. It is intended to be fast and catch obvious
/// cases so that instcombine and other passes are more effective. It is
/// expected that a later pass of GVN will catch the interesting/hard cases.
template<bool UseMemorySSA>
class EarlyCSELegacyCommonPass : public FunctionPass {
public:
static char ID;
EarlyCSELegacyCommonPass() : FunctionPass(ID) {
if (UseMemorySSA)
initializeEarlyCSEMemSSALegacyPassPass(*PassRegistry::getPassRegistry());
else
initializeEarlyCSELegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
auto *MSSA =
UseMemorySSA ? &getAnalysis<MemorySSAWrapperPass>().getMSSA() : nullptr;
EarlyCSE CSE(F.getParent()->getDataLayout(), TLI, TTI, DT, AC, MSSA);
return CSE.run();
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
if (UseMemorySSA) {
AU.addRequired<AAResultsWrapperPass>();
AU.addRequired<MemorySSAWrapperPass>();
AU.addPreserved<MemorySSAWrapperPass>();
}
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addPreserved<AAResultsWrapperPass>();
AU.setPreservesCFG();
}
};
} // end anonymous namespace
using EarlyCSELegacyPass = EarlyCSELegacyCommonPass</*UseMemorySSA=*/false>;
template<>
char EarlyCSELegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(EarlyCSELegacyPass, "early-cse", "Early CSE", false,
false)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(EarlyCSELegacyPass, "early-cse", "Early CSE", false, false)
using EarlyCSEMemSSALegacyPass =
EarlyCSELegacyCommonPass</*UseMemorySSA=*/true>;
template<>
char EarlyCSEMemSSALegacyPass::ID = 0;
FunctionPass *llvm::createEarlyCSEPass(bool UseMemorySSA) {
if (UseMemorySSA)
return new EarlyCSEMemSSALegacyPass();
else
return new EarlyCSELegacyPass();
}
INITIALIZE_PASS_BEGIN(EarlyCSEMemSSALegacyPass, "early-cse-memssa",
"Early CSE w/ MemorySSA", false, false)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
INITIALIZE_PASS_END(EarlyCSEMemSSALegacyPass, "early-cse-memssa",
"Early CSE w/ MemorySSA", false, false)
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