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llvm-mirror/lib/Transforms/Scalar/GVN.cpp
Wei Mi d9cf09c389 [GVN] Recommit the patch "Add phi-translate support in scalarpre" 
Recommit after workaround the bug PR31652.

Three bugs fixed in previous recommits: The first one is to use CurrentBlock
instead of PREInstr's Parent as param of performScalarPREInsertion because
the Parent of a clone instruction may be uninitialized. The second one is stop
PRE when CurrentBlock to its predecessor is a backedge and an operand of CurInst
is defined inside of CurrentBlock. The same value defined inside of loop in last
iteration can not be regarded as available. The third one is an out-of-bound
array access in a flipped if guard.

Right now scalarpre doesn't have phi-translate support, so it will miss some
simple pre opportunities. Like the following testcase, current scalarpre cannot
recognize the last "a * b" is fully redundent because a and b used by the last
"a * b" expr are both defined by phis.

long a[100], b[100], g1, g2, g3;
__attribute__((pure)) long goo();

void foo(long a, long b, long c, long d) {

  g1 = a * b;
  if (__builtin_expect(g2 > 3, 0)) {
    a = c;
    b = d;
    g2 = a * b;
  }
  g3 = a * b;      // fully redundant.

}

The patch adds phi-translate support in scalarpre. This is only a temporary
solution before the newpre based on newgvn is available.

Differential Revision: https://reviews.llvm.org/D32252

llvm-svn: 309397
2017-07-28 15:47:25 +00:00

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//===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs global value numbering to eliminate fully redundant
// instructions. It also performs simple dead load elimination.
//
// Note that this pass does the value numbering itself; it does not use the
// ValueNumbering analysis passes.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/GVN.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Analysis/OptimizationDiagnosticInfo.h"
#include "llvm/Analysis/PHITransAddr.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Transforms/Utils/VNCoercion.h"
#include <vector>
using namespace llvm;
using namespace llvm::gvn;
using namespace llvm::VNCoercion;
using namespace PatternMatch;
#define DEBUG_TYPE "gvn"
STATISTIC(NumGVNInstr, "Number of instructions deleted");
STATISTIC(NumGVNLoad, "Number of loads deleted");
STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
STATISTIC(NumGVNBlocks, "Number of blocks merged");
STATISTIC(NumGVNSimpl, "Number of instructions simplified");
STATISTIC(NumGVNEqProp, "Number of equalities propagated");
STATISTIC(NumPRELoad, "Number of loads PRE'd");
static cl::opt<bool> EnablePRE("enable-pre",
cl::init(true), cl::Hidden);
static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
// Maximum allowed recursion depth.
static cl::opt<uint32_t>
MaxRecurseDepth("max-recurse-depth", cl::Hidden, cl::init(1000), cl::ZeroOrMore,
cl::desc("Max recurse depth (default = 1000)"));
struct llvm::GVN::Expression {
uint32_t opcode;
Type *type;
bool commutative;
SmallVector<uint32_t, 4> varargs;
Expression(uint32_t o = ~2U) : opcode(o), commutative(false) {}
bool operator==(const Expression &other) const {
if (opcode != other.opcode)
return false;
if (opcode == ~0U || opcode == ~1U)
return true;
if (type != other.type)
return false;
if (varargs != other.varargs)
return false;
return true;
}
friend hash_code hash_value(const Expression &Value) {
return hash_combine(
Value.opcode, Value.type,
hash_combine_range(Value.varargs.begin(), Value.varargs.end()));
}
};
namespace llvm {
template <> struct DenseMapInfo<GVN::Expression> {
static inline GVN::Expression getEmptyKey() { return ~0U; }
static inline GVN::Expression getTombstoneKey() { return ~1U; }
static unsigned getHashValue(const GVN::Expression &e) {
using llvm::hash_value;
return static_cast<unsigned>(hash_value(e));
}
static bool isEqual(const GVN::Expression &LHS, const GVN::Expression &RHS) {
return LHS == RHS;
}
};
} // End llvm namespace.
/// Represents a particular available value that we know how to materialize.
/// Materialization of an AvailableValue never fails. An AvailableValue is
/// implicitly associated with a rematerialization point which is the
/// location of the instruction from which it was formed.
struct llvm::gvn::AvailableValue {
enum ValType {
SimpleVal, // A simple offsetted value that is accessed.
LoadVal, // A value produced by a load.
MemIntrin, // A memory intrinsic which is loaded from.
UndefVal // A UndefValue representing a value from dead block (which
// is not yet physically removed from the CFG).
};
/// V - The value that is live out of the block.
PointerIntPair<Value *, 2, ValType> Val;
/// Offset - The byte offset in Val that is interesting for the load query.
unsigned Offset;
static AvailableValue get(Value *V, unsigned Offset = 0) {
AvailableValue Res;
Res.Val.setPointer(V);
Res.Val.setInt(SimpleVal);
Res.Offset = Offset;
return Res;
}
static AvailableValue getMI(MemIntrinsic *MI, unsigned Offset = 0) {
AvailableValue Res;
Res.Val.setPointer(MI);
Res.Val.setInt(MemIntrin);
Res.Offset = Offset;
return Res;
}
static AvailableValue getLoad(LoadInst *LI, unsigned Offset = 0) {
AvailableValue Res;
Res.Val.setPointer(LI);
Res.Val.setInt(LoadVal);
Res.Offset = Offset;
return Res;
}
static AvailableValue getUndef() {
AvailableValue Res;
Res.Val.setPointer(nullptr);
Res.Val.setInt(UndefVal);
Res.Offset = 0;
return Res;
}
bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; }
bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; }
bool isUndefValue() const { return Val.getInt() == UndefVal; }
Value *getSimpleValue() const {
assert(isSimpleValue() && "Wrong accessor");
return Val.getPointer();
}
LoadInst *getCoercedLoadValue() const {
assert(isCoercedLoadValue() && "Wrong accessor");
return cast<LoadInst>(Val.getPointer());
}
MemIntrinsic *getMemIntrinValue() const {
assert(isMemIntrinValue() && "Wrong accessor");
return cast<MemIntrinsic>(Val.getPointer());
}
/// Emit code at the specified insertion point to adjust the value defined
/// here to the specified type. This handles various coercion cases.
Value *MaterializeAdjustedValue(LoadInst *LI, Instruction *InsertPt,
GVN &gvn) const;
};
/// Represents an AvailableValue which can be rematerialized at the end of
/// the associated BasicBlock.
struct llvm::gvn::AvailableValueInBlock {
/// BB - The basic block in question.
BasicBlock *BB;
/// AV - The actual available value
AvailableValue AV;
static AvailableValueInBlock get(BasicBlock *BB, AvailableValue &&AV) {
AvailableValueInBlock Res;
Res.BB = BB;
Res.AV = std::move(AV);
return Res;
}
static AvailableValueInBlock get(BasicBlock *BB, Value *V,
unsigned Offset = 0) {
return get(BB, AvailableValue::get(V, Offset));
}
static AvailableValueInBlock getUndef(BasicBlock *BB) {
return get(BB, AvailableValue::getUndef());
}
/// Emit code at the end of this block to adjust the value defined here to
/// the specified type. This handles various coercion cases.
Value *MaterializeAdjustedValue(LoadInst *LI, GVN &gvn) const {
return AV.MaterializeAdjustedValue(LI, BB->getTerminator(), gvn);
}
};
//===----------------------------------------------------------------------===//
// ValueTable Internal Functions
//===----------------------------------------------------------------------===//
GVN::Expression GVN::ValueTable::createExpr(Instruction *I) {
Expression e;
e.type = I->getType();
e.opcode = I->getOpcode();
for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
OI != OE; ++OI)
e.varargs.push_back(lookupOrAdd(*OI));
if (I->isCommutative()) {
// Ensure that commutative instructions that only differ by a permutation
// of their operands get the same value number by sorting the operand value
// numbers. Since all commutative instructions have two operands it is more
// efficient to sort by hand rather than using, say, std::sort.
assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!");
if (e.varargs[0] > e.varargs[1])
std::swap(e.varargs[0], e.varargs[1]);
e.commutative = true;
}
if (CmpInst *C = dyn_cast<CmpInst>(I)) {
// Sort the operand value numbers so x<y and y>x get the same value number.
CmpInst::Predicate Predicate = C->getPredicate();
if (e.varargs[0] > e.varargs[1]) {
std::swap(e.varargs[0], e.varargs[1]);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
e.opcode = (C->getOpcode() << 8) | Predicate;
e.commutative = true;
} else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) {
for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
II != IE; ++II)
e.varargs.push_back(*II);
}
return e;
}
GVN::Expression GVN::ValueTable::createCmpExpr(unsigned Opcode,
CmpInst::Predicate Predicate,
Value *LHS, Value *RHS) {
assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) &&
"Not a comparison!");
Expression e;
e.type = CmpInst::makeCmpResultType(LHS->getType());
e.varargs.push_back(lookupOrAdd(LHS));
e.varargs.push_back(lookupOrAdd(RHS));
// Sort the operand value numbers so x<y and y>x get the same value number.
if (e.varargs[0] > e.varargs[1]) {
std::swap(e.varargs[0], e.varargs[1]);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
e.opcode = (Opcode << 8) | Predicate;
e.commutative = true;
return e;
}
GVN::Expression GVN::ValueTable::createExtractvalueExpr(ExtractValueInst *EI) {
assert(EI && "Not an ExtractValueInst?");
Expression e;
e.type = EI->getType();
e.opcode = 0;
IntrinsicInst *I = dyn_cast<IntrinsicInst>(EI->getAggregateOperand());
if (I != nullptr && EI->getNumIndices() == 1 && *EI->idx_begin() == 0 ) {
// EI might be an extract from one of our recognised intrinsics. If it
// is we'll synthesize a semantically equivalent expression instead on
// an extract value expression.
switch (I->getIntrinsicID()) {
case Intrinsic::sadd_with_overflow:
case Intrinsic::uadd_with_overflow:
e.opcode = Instruction::Add;
break;
case Intrinsic::ssub_with_overflow:
case Intrinsic::usub_with_overflow:
e.opcode = Instruction::Sub;
break;
case Intrinsic::smul_with_overflow:
case Intrinsic::umul_with_overflow:
e.opcode = Instruction::Mul;
break;
default:
break;
}
if (e.opcode != 0) {
// Intrinsic recognized. Grab its args to finish building the expression.
assert(I->getNumArgOperands() == 2 &&
"Expect two args for recognised intrinsics.");
e.varargs.push_back(lookupOrAdd(I->getArgOperand(0)));
e.varargs.push_back(lookupOrAdd(I->getArgOperand(1)));
return e;
}
}
// Not a recognised intrinsic. Fall back to producing an extract value
// expression.
e.opcode = EI->getOpcode();
for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end();
OI != OE; ++OI)
e.varargs.push_back(lookupOrAdd(*OI));
for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end();
II != IE; ++II)
e.varargs.push_back(*II);
return e;
}
//===----------------------------------------------------------------------===//
// ValueTable External Functions
//===----------------------------------------------------------------------===//
GVN::ValueTable::ValueTable() : nextValueNumber(1) {}
GVN::ValueTable::ValueTable(const ValueTable &) = default;
GVN::ValueTable::ValueTable(ValueTable &&) = default;
GVN::ValueTable::~ValueTable() = default;
/// add - Insert a value into the table with a specified value number.
void GVN::ValueTable::add(Value *V, uint32_t num) {
valueNumbering.insert(std::make_pair(V, num));
if (PHINode *PN = dyn_cast<PHINode>(V))
NumberingPhi[num] = PN;
}
uint32_t GVN::ValueTable::lookupOrAddCall(CallInst *C) {
if (AA->doesNotAccessMemory(C)) {
Expression exp = createExpr(C);
uint32_t e = assignExpNewValueNum(exp).first;
valueNumbering[C] = e;
return e;
} else if (AA->onlyReadsMemory(C)) {
Expression exp = createExpr(C);
auto ValNum = assignExpNewValueNum(exp);
if (ValNum.second) {
valueNumbering[C] = ValNum.first;
return ValNum.first;
}
if (!MD) {
uint32_t e = assignExpNewValueNum(exp).first;
valueNumbering[C] = e;
return e;
}
MemDepResult local_dep = MD->getDependency(C);
if (!local_dep.isDef() && !local_dep.isNonLocal()) {
valueNumbering[C] = nextValueNumber;
return nextValueNumber++;
}
if (local_dep.isDef()) {
CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) {
valueNumbering[C] = nextValueNumber;
return nextValueNumber++;
}
for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
uint32_t c_vn = lookupOrAdd(C->getArgOperand(i));
uint32_t cd_vn = lookupOrAdd(local_cdep->getArgOperand(i));
if (c_vn != cd_vn) {
valueNumbering[C] = nextValueNumber;
return nextValueNumber++;
}
}
uint32_t v = lookupOrAdd(local_cdep);
valueNumbering[C] = v;
return v;
}
// Non-local case.
const MemoryDependenceResults::NonLocalDepInfo &deps =
MD->getNonLocalCallDependency(CallSite(C));
// FIXME: Move the checking logic to MemDep!
CallInst* cdep = nullptr;
// Check to see if we have a single dominating call instruction that is
// identical to C.
for (unsigned i = 0, e = deps.size(); i != e; ++i) {
const NonLocalDepEntry *I = &deps[i];
if (I->getResult().isNonLocal())
continue;
// We don't handle non-definitions. If we already have a call, reject
// instruction dependencies.
if (!I->getResult().isDef() || cdep != nullptr) {
cdep = nullptr;
break;
}
CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
// FIXME: All duplicated with non-local case.
if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
cdep = NonLocalDepCall;
continue;
}
cdep = nullptr;
break;
}
if (!cdep) {
valueNumbering[C] = nextValueNumber;
return nextValueNumber++;
}
if (cdep->getNumArgOperands() != C->getNumArgOperands()) {
valueNumbering[C] = nextValueNumber;
return nextValueNumber++;
}
for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
uint32_t c_vn = lookupOrAdd(C->getArgOperand(i));
uint32_t cd_vn = lookupOrAdd(cdep->getArgOperand(i));
if (c_vn != cd_vn) {
valueNumbering[C] = nextValueNumber;
return nextValueNumber++;
}
}
uint32_t v = lookupOrAdd(cdep);
valueNumbering[C] = v;
return v;
} else {
valueNumbering[C] = nextValueNumber;
return nextValueNumber++;
}
}
/// Returns true if a value number exists for the specified value.
bool GVN::ValueTable::exists(Value *V) const { return valueNumbering.count(V) != 0; }
/// lookup_or_add - Returns the value number for the specified value, assigning
/// it a new number if it did not have one before.
uint32_t GVN::ValueTable::lookupOrAdd(Value *V) {
DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
if (VI != valueNumbering.end())
return VI->second;
if (!isa<Instruction>(V)) {
valueNumbering[V] = nextValueNumber;
return nextValueNumber++;
}
Instruction* I = cast<Instruction>(V);
Expression exp;
switch (I->getOpcode()) {
case Instruction::Call:
return lookupOrAddCall(cast<CallInst>(I));
case Instruction::Add:
case Instruction::FAdd:
case Instruction::Sub:
case Instruction::FSub:
case Instruction::Mul:
case Instruction::FMul:
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::FDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::FRem:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::ICmp:
case Instruction::FCmp:
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::UIToFP:
case Instruction::SIToFP:
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::PtrToInt:
case Instruction::IntToPtr:
case Instruction::BitCast:
case Instruction::Select:
case Instruction::ExtractElement:
case Instruction::InsertElement:
case Instruction::ShuffleVector:
case Instruction::InsertValue:
case Instruction::GetElementPtr:
exp = createExpr(I);
break;
case Instruction::ExtractValue:
exp = createExtractvalueExpr(cast<ExtractValueInst>(I));
break;
case Instruction::PHI:
valueNumbering[V] = nextValueNumber;
NumberingPhi[nextValueNumber] = cast<PHINode>(V);
return nextValueNumber++;
default:
valueNumbering[V] = nextValueNumber;
return nextValueNumber++;
}
uint32_t e = assignExpNewValueNum(exp).first;
valueNumbering[V] = e;
return e;
}
/// Returns the value number of the specified value. Fails if
/// the value has not yet been numbered.
uint32_t GVN::ValueTable::lookup(Value *V, bool Verify) const {
DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
if (Verify) {
assert(VI != valueNumbering.end() && "Value not numbered?");
return VI->second;
}
return (VI != valueNumbering.end()) ? VI->second : 0;
}
/// Returns the value number of the given comparison,
/// assigning it a new number if it did not have one before. Useful when
/// we deduced the result of a comparison, but don't immediately have an
/// instruction realizing that comparison to hand.
uint32_t GVN::ValueTable::lookupOrAddCmp(unsigned Opcode,
CmpInst::Predicate Predicate,
Value *LHS, Value *RHS) {
Expression exp = createCmpExpr(Opcode, Predicate, LHS, RHS);
return assignExpNewValueNum(exp).first;
}
/// Remove all entries from the ValueTable.
void GVN::ValueTable::clear() {
valueNumbering.clear();
expressionNumbering.clear();
NumberingPhi.clear();
PhiTranslateTable.clear();
nextValueNumber = 1;
Expressions.clear();
ExprIdx.clear();
nextExprNumber = 0;
}
/// Remove a value from the value numbering.
void GVN::ValueTable::erase(Value *V) {
uint32_t Num = valueNumbering.lookup(V);
valueNumbering.erase(V);
// If V is PHINode, V <--> value number is an one-to-one mapping.
if (isa<PHINode>(V))
NumberingPhi.erase(Num);
}
/// verifyRemoved - Verify that the value is removed from all internal data
/// structures.
void GVN::ValueTable::verifyRemoved(const Value *V) const {
for (DenseMap<Value*, uint32_t>::const_iterator
I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
assert(I->first != V && "Inst still occurs in value numbering map!");
}
}
//===----------------------------------------------------------------------===//
// GVN Pass
//===----------------------------------------------------------------------===//
PreservedAnalyses GVN::run(Function &F, FunctionAnalysisManager &AM) {
// FIXME: The order of evaluation of these 'getResult' calls is very
// significant! Re-ordering these variables will cause GVN when run alone to
// be less effective! We should fix memdep and basic-aa to not exhibit this
// behavior, but until then don't change the order here.
auto &AC = AM.getResult<AssumptionAnalysis>(F);
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &AA = AM.getResult<AAManager>(F);
auto &MemDep = AM.getResult<MemoryDependenceAnalysis>(F);
auto *LI = AM.getCachedResult<LoopAnalysis>(F);
auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
bool Changed = runImpl(F, AC, DT, TLI, AA, &MemDep, LI, &ORE);
if (!Changed)
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserve<DominatorTreeAnalysis>();
PA.preserve<GlobalsAA>();
PA.preserve<TargetLibraryAnalysis>();
return PA;
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void GVN::dump(DenseMap<uint32_t, Value*>& d) const {
errs() << "{\n";
for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
E = d.end(); I != E; ++I) {
errs() << I->first << "\n";
I->second->dump();
}
errs() << "}\n";
}
#endif
/// Return true if we can prove that the value
/// we're analyzing is fully available in the specified block. As we go, keep
/// track of which blocks we know are fully alive in FullyAvailableBlocks. This
/// map is actually a tri-state map with the following values:
/// 0) we know the block *is not* fully available.
/// 1) we know the block *is* fully available.
/// 2) we do not know whether the block is fully available or not, but we are
/// currently speculating that it will be.
/// 3) we are speculating for this block and have used that to speculate for
/// other blocks.
static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
DenseMap<BasicBlock*, char> &FullyAvailableBlocks,
uint32_t RecurseDepth) {
if (RecurseDepth > MaxRecurseDepth)
return false;
// Optimistically assume that the block is fully available and check to see
// if we already know about this block in one lookup.
std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
FullyAvailableBlocks.insert(std::make_pair(BB, 2));
// If the entry already existed for this block, return the precomputed value.
if (!IV.second) {
// If this is a speculative "available" value, mark it as being used for
// speculation of other blocks.
if (IV.first->second == 2)
IV.first->second = 3;
return IV.first->second != 0;
}
// Otherwise, see if it is fully available in all predecessors.
pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
// If this block has no predecessors, it isn't live-in here.
if (PI == PE)
goto SpeculationFailure;
for (; PI != PE; ++PI)
// If the value isn't fully available in one of our predecessors, then it
// isn't fully available in this block either. Undo our previous
// optimistic assumption and bail out.
if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks,RecurseDepth+1))
goto SpeculationFailure;
return true;
// If we get here, we found out that this is not, after
// all, a fully-available block. We have a problem if we speculated on this and
// used the speculation to mark other blocks as available.
SpeculationFailure:
char &BBVal = FullyAvailableBlocks[BB];
// If we didn't speculate on this, just return with it set to false.
if (BBVal == 2) {
BBVal = 0;
return false;
}
// If we did speculate on this value, we could have blocks set to 1 that are
// incorrect. Walk the (transitive) successors of this block and mark them as
// 0 if set to one.
SmallVector<BasicBlock*, 32> BBWorklist;
BBWorklist.push_back(BB);
do {
BasicBlock *Entry = BBWorklist.pop_back_val();
// Note that this sets blocks to 0 (unavailable) if they happen to not
// already be in FullyAvailableBlocks. This is safe.
char &EntryVal = FullyAvailableBlocks[Entry];
if (EntryVal == 0) continue; // Already unavailable.
// Mark as unavailable.
EntryVal = 0;
BBWorklist.append(succ_begin(Entry), succ_end(Entry));
} while (!BBWorklist.empty());
return false;
}
/// Given a set of loads specified by ValuesPerBlock,
/// construct SSA form, allowing us to eliminate LI. This returns the value
/// that should be used at LI's definition site.
static Value *ConstructSSAForLoadSet(LoadInst *LI,
SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
GVN &gvn) {
// Check for the fully redundant, dominating load case. In this case, we can
// just use the dominating value directly.
if (ValuesPerBlock.size() == 1 &&
gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB,
LI->getParent())) {
assert(!ValuesPerBlock[0].AV.isUndefValue() &&
"Dead BB dominate this block");
return ValuesPerBlock[0].MaterializeAdjustedValue(LI, gvn);
}
// Otherwise, we have to construct SSA form.
SmallVector<PHINode*, 8> NewPHIs;
SSAUpdater SSAUpdate(&NewPHIs);
SSAUpdate.Initialize(LI->getType(), LI->getName());
for (const AvailableValueInBlock &AV : ValuesPerBlock) {
BasicBlock *BB = AV.BB;
if (SSAUpdate.HasValueForBlock(BB))
continue;
SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LI, gvn));
}
// Perform PHI construction.
return SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
}
Value *AvailableValue::MaterializeAdjustedValue(LoadInst *LI,
Instruction *InsertPt,
GVN &gvn) const {
Value *Res;
Type *LoadTy = LI->getType();
const DataLayout &DL = LI->getModule()->getDataLayout();
if (isSimpleValue()) {
Res = getSimpleValue();
if (Res->getType() != LoadTy) {
Res = getStoreValueForLoad(Res, Offset, LoadTy, InsertPt, DL);
DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
<< *getSimpleValue() << '\n'
<< *Res << '\n' << "\n\n\n");
}
} else if (isCoercedLoadValue()) {
LoadInst *Load = getCoercedLoadValue();
if (Load->getType() == LoadTy && Offset == 0) {
Res = Load;
} else {
Res = getLoadValueForLoad(Load, Offset, LoadTy, InsertPt, DL);
// We would like to use gvn.markInstructionForDeletion here, but we can't
// because the load is already memoized into the leader map table that GVN
// tracks. It is potentially possible to remove the load from the table,
// but then there all of the operations based on it would need to be
// rehashed. Just leave the dead load around.
gvn.getMemDep().removeInstruction(Load);
DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset << " "
<< *getCoercedLoadValue() << '\n'
<< *Res << '\n'
<< "\n\n\n");
}
} else if (isMemIntrinValue()) {
Res = getMemInstValueForLoad(getMemIntrinValue(), Offset, LoadTy,
InsertPt, DL);
DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
<< " " << *getMemIntrinValue() << '\n'
<< *Res << '\n' << "\n\n\n");
} else {
assert(isUndefValue() && "Should be UndefVal");
DEBUG(dbgs() << "GVN COERCED NONLOCAL Undef:\n";);
return UndefValue::get(LoadTy);
}
assert(Res && "failed to materialize?");
return Res;
}
static bool isLifetimeStart(const Instruction *Inst) {
if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
return II->getIntrinsicID() == Intrinsic::lifetime_start;
return false;
}
/// \brief Try to locate the three instruction involved in a missed
/// load-elimination case that is due to an intervening store.
static void reportMayClobberedLoad(LoadInst *LI, MemDepResult DepInfo,
DominatorTree *DT,
OptimizationRemarkEmitter *ORE) {
using namespace ore;
User *OtherAccess = nullptr;
OptimizationRemarkMissed R(DEBUG_TYPE, "LoadClobbered", LI);
R << "load of type " << NV("Type", LI->getType()) << " not eliminated"
<< setExtraArgs();
for (auto *U : LI->getPointerOperand()->users())
if (U != LI && (isa<LoadInst>(U) || isa<StoreInst>(U)) &&
DT->dominates(cast<Instruction>(U), LI)) {
// FIXME: for now give up if there are multiple memory accesses that
// dominate the load. We need further analysis to decide which one is
// that we're forwarding from.
if (OtherAccess)
OtherAccess = nullptr;
else
OtherAccess = U;
}
if (OtherAccess)
R << " in favor of " << NV("OtherAccess", OtherAccess);
R << " because it is clobbered by " << NV("ClobberedBy", DepInfo.getInst());
ORE->emit(R);
}
bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
Value *Address, AvailableValue &Res) {
assert((DepInfo.isDef() || DepInfo.isClobber()) &&
"expected a local dependence");
assert(LI->isUnordered() && "rules below are incorrect for ordered access");
const DataLayout &DL = LI->getModule()->getDataLayout();
if (DepInfo.isClobber()) {
// If the dependence is to a store that writes to a superset of the bits
// read by the load, we can extract the bits we need for the load from the
// stored value.
if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
// Can't forward from non-atomic to atomic without violating memory model.
if (Address && LI->isAtomic() <= DepSI->isAtomic()) {
int Offset =
analyzeLoadFromClobberingStore(LI->getType(), Address, DepSI, DL);
if (Offset != -1) {
Res = AvailableValue::get(DepSI->getValueOperand(), Offset);
return true;
}
}
}
// Check to see if we have something like this:
// load i32* P
// load i8* (P+1)
// if we have this, replace the later with an extraction from the former.
if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) {
// If this is a clobber and L is the first instruction in its block, then
// we have the first instruction in the entry block.
// Can't forward from non-atomic to atomic without violating memory model.
if (DepLI != LI && Address && LI->isAtomic() <= DepLI->isAtomic()) {
int Offset =
analyzeLoadFromClobberingLoad(LI->getType(), Address, DepLI, DL);
if (Offset != -1) {
Res = AvailableValue::getLoad(DepLI, Offset);
return true;
}
}
}
// If the clobbering value is a memset/memcpy/memmove, see if we can
// forward a value on from it.
if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
if (Address && !LI->isAtomic()) {
int Offset = analyzeLoadFromClobberingMemInst(LI->getType(), Address,
DepMI, DL);
if (Offset != -1) {
Res = AvailableValue::getMI(DepMI, Offset);
return true;
}
}
}
// Nothing known about this clobber, have to be conservative
DEBUG(
// fast print dep, using operator<< on instruction is too slow.
dbgs() << "GVN: load ";
LI->printAsOperand(dbgs());
Instruction *I = DepInfo.getInst();
dbgs() << " is clobbered by " << *I << '\n';
);
if (ORE->allowExtraAnalysis())
reportMayClobberedLoad(LI, DepInfo, DT, ORE);
return false;
}
assert(DepInfo.isDef() && "follows from above");
Instruction *DepInst = DepInfo.getInst();
// Loading the allocation -> undef.
if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI) ||
// Loading immediately after lifetime begin -> undef.
isLifetimeStart(DepInst)) {
Res = AvailableValue::get(UndefValue::get(LI->getType()));
return true;
}
// Loading from calloc (which zero initializes memory) -> zero
if (isCallocLikeFn(DepInst, TLI)) {
Res = AvailableValue::get(Constant::getNullValue(LI->getType()));
return true;
}
if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
// Reject loads and stores that are to the same address but are of
// different types if we have to. If the stored value is larger or equal to
// the loaded value, we can reuse it.
if (S->getValueOperand()->getType() != LI->getType() &&
!canCoerceMustAliasedValueToLoad(S->getValueOperand(),
LI->getType(), DL))
return false;
// Can't forward from non-atomic to atomic without violating memory model.
if (S->isAtomic() < LI->isAtomic())
return false;
Res = AvailableValue::get(S->getValueOperand());
return true;
}
if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
// If the types mismatch and we can't handle it, reject reuse of the load.
// If the stored value is larger or equal to the loaded value, we can reuse
// it.
if (LD->getType() != LI->getType() &&
!canCoerceMustAliasedValueToLoad(LD, LI->getType(), DL))
return false;
// Can't forward from non-atomic to atomic without violating memory model.
if (LD->isAtomic() < LI->isAtomic())
return false;
Res = AvailableValue::getLoad(LD);
return true;
}
// Unknown def - must be conservative
DEBUG(
// fast print dep, using operator<< on instruction is too slow.
dbgs() << "GVN: load ";
LI->printAsOperand(dbgs());
dbgs() << " has unknown def " << *DepInst << '\n';
);
return false;
}
void GVN::AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps,
AvailValInBlkVect &ValuesPerBlock,
UnavailBlkVect &UnavailableBlocks) {
// Filter out useless results (non-locals, etc). Keep track of the blocks
// where we have a value available in repl, also keep track of whether we see
// dependencies that produce an unknown value for the load (such as a call
// that could potentially clobber the load).
unsigned NumDeps = Deps.size();
for (unsigned i = 0, e = NumDeps; i != e; ++i) {
BasicBlock *DepBB = Deps[i].getBB();
MemDepResult DepInfo = Deps[i].getResult();
if (DeadBlocks.count(DepBB)) {
// Dead dependent mem-op disguise as a load evaluating the same value
// as the load in question.
ValuesPerBlock.push_back(AvailableValueInBlock::getUndef(DepBB));
continue;
}
if (!DepInfo.isDef() && !DepInfo.isClobber()) {
UnavailableBlocks.push_back(DepBB);
continue;
}
// The address being loaded in this non-local block may not be the same as
// the pointer operand of the load if PHI translation occurs. Make sure
// to consider the right address.
Value *Address = Deps[i].getAddress();
AvailableValue AV;
if (AnalyzeLoadAvailability(LI, DepInfo, Address, AV)) {
// subtlety: because we know this was a non-local dependency, we know
// it's safe to materialize anywhere between the instruction within
// DepInfo and the end of it's block.
ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
std::move(AV)));
} else {
UnavailableBlocks.push_back(DepBB);
}
}
assert(NumDeps == ValuesPerBlock.size() + UnavailableBlocks.size() &&
"post condition violation");
}
bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
UnavailBlkVect &UnavailableBlocks) {
// Okay, we have *some* definitions of the value. This means that the value
// is available in some of our (transitive) predecessors. Lets think about
// doing PRE of this load. This will involve inserting a new load into the
// predecessor when it's not available. We could do this in general, but
// prefer to not increase code size. As such, we only do this when we know
// that we only have to insert *one* load (which means we're basically moving
// the load, not inserting a new one).
SmallPtrSet<BasicBlock *, 4> Blockers(UnavailableBlocks.begin(),
UnavailableBlocks.end());
// Let's find the first basic block with more than one predecessor. Walk
// backwards through predecessors if needed.
BasicBlock *LoadBB = LI->getParent();
BasicBlock *TmpBB = LoadBB;
while (TmpBB->getSinglePredecessor()) {
TmpBB = TmpBB->getSinglePredecessor();
if (TmpBB == LoadBB) // Infinite (unreachable) loop.
return false;
if (Blockers.count(TmpBB))
return false;
// If any of these blocks has more than one successor (i.e. if the edge we
// just traversed was critical), then there are other paths through this
// block along which the load may not be anticipated. Hoisting the load
// above this block would be adding the load to execution paths along
// which it was not previously executed.
if (TmpBB->getTerminator()->getNumSuccessors() != 1)
return false;
}
assert(TmpBB);
LoadBB = TmpBB;
// Check to see how many predecessors have the loaded value fully
// available.
MapVector<BasicBlock *, Value *> PredLoads;
DenseMap<BasicBlock*, char> FullyAvailableBlocks;
for (const AvailableValueInBlock &AV : ValuesPerBlock)
FullyAvailableBlocks[AV.BB] = true;
for (BasicBlock *UnavailableBB : UnavailableBlocks)
FullyAvailableBlocks[UnavailableBB] = false;
SmallVector<BasicBlock *, 4> CriticalEdgePred;
for (BasicBlock *Pred : predecessors(LoadBB)) {
// If any predecessor block is an EH pad that does not allow non-PHI
// instructions before the terminator, we can't PRE the load.
if (Pred->getTerminator()->isEHPad()) {
DEBUG(dbgs()
<< "COULD NOT PRE LOAD BECAUSE OF AN EH PAD PREDECESSOR '"
<< Pred->getName() << "': " << *LI << '\n');
return false;
}
if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks, 0)) {
continue;
}
if (Pred->getTerminator()->getNumSuccessors() != 1) {
if (isa<IndirectBrInst>(Pred->getTerminator())) {
DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
<< Pred->getName() << "': " << *LI << '\n');
return false;
}
if (LoadBB->isEHPad()) {
DEBUG(dbgs()
<< "COULD NOT PRE LOAD BECAUSE OF AN EH PAD CRITICAL EDGE '"
<< Pred->getName() << "': " << *LI << '\n');
return false;
}
CriticalEdgePred.push_back(Pred);
} else {
// Only add the predecessors that will not be split for now.
PredLoads[Pred] = nullptr;
}
}
// Decide whether PRE is profitable for this load.
unsigned NumUnavailablePreds = PredLoads.size() + CriticalEdgePred.size();
assert(NumUnavailablePreds != 0 &&
"Fully available value should already be eliminated!");
// If this load is unavailable in multiple predecessors, reject it.
// FIXME: If we could restructure the CFG, we could make a common pred with
// all the preds that don't have an available LI and insert a new load into
// that one block.
if (NumUnavailablePreds != 1)
return false;
// Split critical edges, and update the unavailable predecessors accordingly.
for (BasicBlock *OrigPred : CriticalEdgePred) {
BasicBlock *NewPred = splitCriticalEdges(OrigPred, LoadBB);
assert(!PredLoads.count(OrigPred) && "Split edges shouldn't be in map!");
PredLoads[NewPred] = nullptr;
DEBUG(dbgs() << "Split critical edge " << OrigPred->getName() << "->"
<< LoadBB->getName() << '\n');
}
// Check if the load can safely be moved to all the unavailable predecessors.
bool CanDoPRE = true;
const DataLayout &DL = LI->getModule()->getDataLayout();
SmallVector<Instruction*, 8> NewInsts;
for (auto &PredLoad : PredLoads) {
BasicBlock *UnavailablePred = PredLoad.first;
// Do PHI translation to get its value in the predecessor if necessary. The
// returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
// If all preds have a single successor, then we know it is safe to insert
// the load on the pred (?!?), so we can insert code to materialize the
// pointer if it is not available.
PHITransAddr Address(LI->getPointerOperand(), DL, AC);
Value *LoadPtr = nullptr;
LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
*DT, NewInsts);
// If we couldn't find or insert a computation of this phi translated value,
// we fail PRE.
if (!LoadPtr) {
DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
<< *LI->getPointerOperand() << "\n");
CanDoPRE = false;
break;
}
PredLoad.second = LoadPtr;
}
if (!CanDoPRE) {
while (!NewInsts.empty()) {
Instruction *I = NewInsts.pop_back_val();
if (MD) MD->removeInstruction(I);
I->eraseFromParent();
}
// HINT: Don't revert the edge-splitting as following transformation may
// also need to split these critical edges.
return !CriticalEdgePred.empty();
}
// Okay, we can eliminate this load by inserting a reload in the predecessor
// and using PHI construction to get the value in the other predecessors, do
// it.
DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
DEBUG(if (!NewInsts.empty())
dbgs() << "INSERTED " << NewInsts.size() << " INSTS: "
<< *NewInsts.back() << '\n');
// Assign value numbers to the new instructions.
for (Instruction *I : NewInsts) {
// Instructions that have been inserted in predecessor(s) to materialize
// the load address do not retain their original debug locations. Doing
// so could lead to confusing (but correct) source attributions.
// FIXME: How do we retain source locations without causing poor debugging
// behavior?
I->setDebugLoc(DebugLoc());
// FIXME: We really _ought_ to insert these value numbers into their
// parent's availability map. However, in doing so, we risk getting into
// ordering issues. If a block hasn't been processed yet, we would be
// marking a value as AVAIL-IN, which isn't what we intend.
VN.lookupOrAdd(I);
}
for (const auto &PredLoad : PredLoads) {
BasicBlock *UnavailablePred = PredLoad.first;
Value *LoadPtr = PredLoad.second;
auto *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre",
LI->isVolatile(), LI->getAlignment(),
LI->getOrdering(), LI->getSyncScopeID(),
UnavailablePred->getTerminator());
NewLoad->setDebugLoc(LI->getDebugLoc());
// Transfer the old load's AA tags to the new load.
AAMDNodes Tags;
LI->getAAMetadata(Tags);
if (Tags)
NewLoad->setAAMetadata(Tags);
if (auto *MD = LI->getMetadata(LLVMContext::MD_invariant_load))
NewLoad->setMetadata(LLVMContext::MD_invariant_load, MD);
if (auto *InvGroupMD = LI->getMetadata(LLVMContext::MD_invariant_group))
NewLoad->setMetadata(LLVMContext::MD_invariant_group, InvGroupMD);
if (auto *RangeMD = LI->getMetadata(LLVMContext::MD_range))
NewLoad->setMetadata(LLVMContext::MD_range, RangeMD);
// We do not propagate the old load's debug location, because the new
// load now lives in a different BB, and we want to avoid a jumpy line
// table.
// FIXME: How do we retain source locations without causing poor debugging
// behavior?
// Add the newly created load.
ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
NewLoad));
MD->invalidateCachedPointerInfo(LoadPtr);
DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
}
// Perform PHI construction.
Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this);
LI->replaceAllUsesWith(V);
if (isa<PHINode>(V))
V->takeName(LI);
if (Instruction *I = dyn_cast<Instruction>(V))
I->setDebugLoc(LI->getDebugLoc());
if (V->getType()->isPtrOrPtrVectorTy())
MD->invalidateCachedPointerInfo(V);
markInstructionForDeletion(LI);
ORE->emit(OptimizationRemark(DEBUG_TYPE, "LoadPRE", LI)
<< "load eliminated by PRE");
++NumPRELoad;
return true;
}
static void reportLoadElim(LoadInst *LI, Value *AvailableValue,
OptimizationRemarkEmitter *ORE) {
using namespace ore;
ORE->emit(OptimizationRemark(DEBUG_TYPE, "LoadElim", LI)
<< "load of type " << NV("Type", LI->getType()) << " eliminated"
<< setExtraArgs() << " in favor of "
<< NV("InfavorOfValue", AvailableValue));
}
/// Attempt to eliminate a load whose dependencies are
/// non-local by performing PHI construction.
bool GVN::processNonLocalLoad(LoadInst *LI) {
// non-local speculations are not allowed under asan.
if (LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeAddress))
return false;
// Step 1: Find the non-local dependencies of the load.
LoadDepVect Deps;
MD->getNonLocalPointerDependency(LI, Deps);
// If we had to process more than one hundred blocks to find the
// dependencies, this load isn't worth worrying about. Optimizing
// it will be too expensive.
unsigned NumDeps = Deps.size();
if (NumDeps > 100)
return false;
// If we had a phi translation failure, we'll have a single entry which is a
// clobber in the current block. Reject this early.
if (NumDeps == 1 &&
!Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) {
DEBUG(
dbgs() << "GVN: non-local load ";
LI->printAsOperand(dbgs());
dbgs() << " has unknown dependencies\n";
);
return false;
}
// If this load follows a GEP, see if we can PRE the indices before analyzing.
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0))) {
for (GetElementPtrInst::op_iterator OI = GEP->idx_begin(),
OE = GEP->idx_end();
OI != OE; ++OI)
if (Instruction *I = dyn_cast<Instruction>(OI->get()))
performScalarPRE(I);
}
// Step 2: Analyze the availability of the load
AvailValInBlkVect ValuesPerBlock;
UnavailBlkVect UnavailableBlocks;
AnalyzeLoadAvailability(LI, Deps, ValuesPerBlock, UnavailableBlocks);
// If we have no predecessors that produce a known value for this load, exit
// early.
if (ValuesPerBlock.empty())
return false;
// Step 3: Eliminate fully redundancy.
//
// If all of the instructions we depend on produce a known value for this
// load, then it is fully redundant and we can use PHI insertion to compute
// its value. Insert PHIs and remove the fully redundant value now.
if (UnavailableBlocks.empty()) {
DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
// Perform PHI construction.
Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this);
LI->replaceAllUsesWith(V);
if (isa<PHINode>(V))
V->takeName(LI);
if (Instruction *I = dyn_cast<Instruction>(V))
// If instruction I has debug info, then we should not update it.
// Also, if I has a null DebugLoc, then it is still potentially incorrect
// to propagate LI's DebugLoc because LI may not post-dominate I.
if (LI->getDebugLoc() && LI->getParent() == I->getParent())
I->setDebugLoc(LI->getDebugLoc());
if (V->getType()->isPtrOrPtrVectorTy())
MD->invalidateCachedPointerInfo(V);
markInstructionForDeletion(LI);
++NumGVNLoad;
reportLoadElim(LI, V, ORE);
return true;
}
// Step 4: Eliminate partial redundancy.
if (!EnablePRE || !EnableLoadPRE)
return false;
return PerformLoadPRE(LI, ValuesPerBlock, UnavailableBlocks);
}
bool GVN::processAssumeIntrinsic(IntrinsicInst *IntrinsicI) {
assert(IntrinsicI->getIntrinsicID() == Intrinsic::assume &&
"This function can only be called with llvm.assume intrinsic");
Value *V = IntrinsicI->getArgOperand(0);
if (ConstantInt *Cond = dyn_cast<ConstantInt>(V)) {
if (Cond->isZero()) {
Type *Int8Ty = Type::getInt8Ty(V->getContext());
// Insert a new store to null instruction before the load to indicate that
// this code is not reachable. FIXME: We could insert unreachable
// instruction directly because we can modify the CFG.
new StoreInst(UndefValue::get(Int8Ty),
Constant::getNullValue(Int8Ty->getPointerTo()),
IntrinsicI);
}
markInstructionForDeletion(IntrinsicI);
return false;
}
Constant *True = ConstantInt::getTrue(V->getContext());
bool Changed = false;
for (BasicBlock *Successor : successors(IntrinsicI->getParent())) {
BasicBlockEdge Edge(IntrinsicI->getParent(), Successor);
// This property is only true in dominated successors, propagateEquality
// will check dominance for us.
Changed |= propagateEquality(V, True, Edge, false);
}
// We can replace assume value with true, which covers cases like this:
// call void @llvm.assume(i1 %cmp)
// br i1 %cmp, label %bb1, label %bb2 ; will change %cmp to true
ReplaceWithConstMap[V] = True;
// If one of *cmp *eq operand is const, adding it to map will cover this:
// %cmp = fcmp oeq float 3.000000e+00, %0 ; const on lhs could happen
// call void @llvm.assume(i1 %cmp)
// ret float %0 ; will change it to ret float 3.000000e+00
if (auto *CmpI = dyn_cast<CmpInst>(V)) {
if (CmpI->getPredicate() == CmpInst::Predicate::ICMP_EQ ||
CmpI->getPredicate() == CmpInst::Predicate::FCMP_OEQ ||
(CmpI->getPredicate() == CmpInst::Predicate::FCMP_UEQ &&
CmpI->getFastMathFlags().noNaNs())) {
Value *CmpLHS = CmpI->getOperand(0);
Value *CmpRHS = CmpI->getOperand(1);
if (isa<Constant>(CmpLHS))
std::swap(CmpLHS, CmpRHS);
auto *RHSConst = dyn_cast<Constant>(CmpRHS);
// If only one operand is constant.
if (RHSConst != nullptr && !isa<Constant>(CmpLHS))
ReplaceWithConstMap[CmpLHS] = RHSConst;
}
}
return Changed;
}
static void patchReplacementInstruction(Instruction *I, Value *Repl) {
auto *ReplInst = dyn_cast<Instruction>(Repl);
if (!ReplInst)
return;
// Patch the replacement so that it is not more restrictive than the value
// being replaced.
// Note that if 'I' is a load being replaced by some operation,
// for example, by an arithmetic operation, then andIRFlags()
// would just erase all math flags from the original arithmetic
// operation, which is clearly not wanted and not needed.
if (!isa<LoadInst>(I))
ReplInst->andIRFlags(I);
// FIXME: If both the original and replacement value are part of the
// same control-flow region (meaning that the execution of one
// guarantees the execution of the other), then we can combine the
// noalias scopes here and do better than the general conservative
// answer used in combineMetadata().
// In general, GVN unifies expressions over different control-flow
// regions, and so we need a conservative combination of the noalias
// scopes.
static const unsigned KnownIDs[] = {
LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
LLVMContext::MD_noalias, LLVMContext::MD_range,
LLVMContext::MD_fpmath, LLVMContext::MD_invariant_load,
LLVMContext::MD_invariant_group};
combineMetadata(ReplInst, I, KnownIDs);
}
static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) {
patchReplacementInstruction(I, Repl);
I->replaceAllUsesWith(Repl);
}
/// Attempt to eliminate a load, first by eliminating it
/// locally, and then attempting non-local elimination if that fails.
bool GVN::processLoad(LoadInst *L) {
if (!MD)
return false;
// This code hasn't been audited for ordered or volatile memory access
if (!L->isUnordered())
return false;
if (L->use_empty()) {
markInstructionForDeletion(L);
return true;
}
// ... to a pointer that has been loaded from before...
MemDepResult Dep = MD->getDependency(L);
// If it is defined in another block, try harder.
if (Dep.isNonLocal())
return processNonLocalLoad(L);
// Only handle the local case below
if (!Dep.isDef() && !Dep.isClobber()) {
// This might be a NonFuncLocal or an Unknown
DEBUG(
// fast print dep, using operator<< on instruction is too slow.
dbgs() << "GVN: load ";
L->printAsOperand(dbgs());
dbgs() << " has unknown dependence\n";
);
return false;
}
AvailableValue AV;
if (AnalyzeLoadAvailability(L, Dep, L->getPointerOperand(), AV)) {
Value *AvailableValue = AV.MaterializeAdjustedValue(L, L, *this);
// Replace the load!
patchAndReplaceAllUsesWith(L, AvailableValue);
markInstructionForDeletion(L);
++NumGVNLoad;
reportLoadElim(L, AvailableValue, ORE);
// Tell MDA to rexamine the reused pointer since we might have more
// information after forwarding it.
if (MD && AvailableValue->getType()->isPtrOrPtrVectorTy())
MD->invalidateCachedPointerInfo(AvailableValue);
return true;
}
return false;
}
/// Return a pair the first field showing the value number of \p Exp and the
/// second field showing whether it is a value number newly created.
std::pair<uint32_t, bool>
GVN::ValueTable::assignExpNewValueNum(Expression &Exp) {
uint32_t &e = expressionNumbering[Exp];
bool CreateNewValNum = !e;
if (CreateNewValNum) {
Expressions.push_back(Exp);
if (ExprIdx.size() < nextValueNumber + 1)
ExprIdx.resize(nextValueNumber * 2);
e = nextValueNumber;
ExprIdx[nextValueNumber++] = nextExprNumber++;
}
return {e, CreateNewValNum};
}
/// Return whether all the values related with the same \p num are
/// defined in \p BB.
bool GVN::ValueTable::areAllValsInBB(uint32_t Num, const BasicBlock *BB,
GVN &Gvn) {
LeaderTableEntry *Vals = &Gvn.LeaderTable[Num];
while (Vals && Vals->BB == BB)
Vals = Vals->Next;
return !Vals;
}
/// Wrap phiTranslateImpl to provide caching functionality.
uint32_t GVN::ValueTable::phiTranslate(const BasicBlock *Pred,
const BasicBlock *PhiBlock, uint32_t Num,
GVN &Gvn) {
auto FindRes = PhiTranslateTable.find({Num, Pred});
if (FindRes != PhiTranslateTable.end())
return FindRes->second;
uint32_t NewNum = phiTranslateImpl(Pred, PhiBlock, Num, Gvn);
PhiTranslateTable.insert({{Num, Pred}, NewNum});
return NewNum;
}
/// Translate value number \p Num using phis, so that it has the values of
/// the phis in BB.
uint32_t GVN::ValueTable::phiTranslateImpl(const BasicBlock *Pred,
const BasicBlock *PhiBlock,
uint32_t Num, GVN &Gvn) {
if (PHINode *PN = NumberingPhi[Num]) {
for (unsigned i = 0; i != PN->getNumIncomingValues(); ++i) {
if (PN->getParent() == PhiBlock && PN->getIncomingBlock(i) == Pred)
if (uint32_t TransVal = lookup(PN->getIncomingValue(i), false))
return TransVal;
}
return Num;
}
// If there is any value related with Num is defined in a BB other than
// PhiBlock, it cannot depend on a phi in PhiBlock without going through
// a backedge. We can do an early exit in that case to save compile time.
if (!areAllValsInBB(Num, PhiBlock, Gvn))
return Num;
if (Num >= ExprIdx.size() || ExprIdx[Num] == 0)
return Num;
Expression Exp = Expressions[ExprIdx[Num]];
for (unsigned i = 0; i < Exp.varargs.size(); i++) {
// For InsertValue and ExtractValue, some varargs are index numbers
// instead of value numbers. Those index numbers should not be
// translated.
if ((i > 1 && Exp.opcode == Instruction::InsertValue) ||
(i > 0 && Exp.opcode == Instruction::ExtractValue))
continue;
Exp.varargs[i] = phiTranslate(Pred, PhiBlock, Exp.varargs[i], Gvn);
}
if (Exp.commutative) {
assert(Exp.varargs.size() == 2 && "Unsupported commutative expression!");
if (Exp.varargs[0] > Exp.varargs[1]) {
std::swap(Exp.varargs[0], Exp.varargs[1]);
uint32_t Opcode = Exp.opcode >> 8;
if (Opcode == Instruction::ICmp || Opcode == Instruction::FCmp)
Exp.opcode = (Opcode << 8) |
CmpInst::getSwappedPredicate(
static_cast<CmpInst::Predicate>(Exp.opcode & 255));
}
}
if (uint32_t NewNum = expressionNumbering[Exp])
return NewNum;
return Num;
}
// In order to find a leader for a given value number at a
// specific basic block, we first obtain the list of all Values for that number,
// and then scan the list to find one whose block dominates the block in
// question. This is fast because dominator tree queries consist of only
// a few comparisons of DFS numbers.
Value *GVN::findLeader(const BasicBlock *BB, uint32_t num) {
LeaderTableEntry Vals = LeaderTable[num];
if (!Vals.Val) return nullptr;
Value *Val = nullptr;
if (DT->dominates(Vals.BB, BB)) {
Val = Vals.Val;
if (isa<Constant>(Val)) return Val;
}
LeaderTableEntry* Next = Vals.Next;
while (Next) {
if (DT->dominates(Next->BB, BB)) {
if (isa<Constant>(Next->Val)) return Next->Val;
if (!Val) Val = Next->Val;
}
Next = Next->Next;
}
return Val;
}
/// There is an edge from 'Src' to 'Dst'. Return
/// true if every path from the entry block to 'Dst' passes via this edge. In
/// particular 'Dst' must not be reachable via another edge from 'Src'.
static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E,
DominatorTree *DT) {
// While in theory it is interesting to consider the case in which Dst has
// more than one predecessor, because Dst might be part of a loop which is
// only reachable from Src, in practice it is pointless since at the time
// GVN runs all such loops have preheaders, which means that Dst will have
// been changed to have only one predecessor, namely Src.
const BasicBlock *Pred = E.getEnd()->getSinglePredecessor();
assert((!Pred || Pred == E.getStart()) &&
"No edge between these basic blocks!");
return Pred != nullptr;
}
void GVN::assignBlockRPONumber(Function &F) {
uint32_t NextBlockNumber = 1;
ReversePostOrderTraversal<Function *> RPOT(&F);
for (BasicBlock *BB : RPOT)
BlockRPONumber[BB] = NextBlockNumber++;
}
// Tries to replace instruction with const, using information from
// ReplaceWithConstMap.
bool GVN::replaceOperandsWithConsts(Instruction *Instr) const {
bool Changed = false;
for (unsigned OpNum = 0; OpNum < Instr->getNumOperands(); ++OpNum) {
Value *Operand = Instr->getOperand(OpNum);
auto it = ReplaceWithConstMap.find(Operand);
if (it != ReplaceWithConstMap.end()) {
assert(!isa<Constant>(Operand) &&
"Replacing constants with constants is invalid");
DEBUG(dbgs() << "GVN replacing: " << *Operand << " with " << *it->second
<< " in instruction " << *Instr << '\n');
Instr->setOperand(OpNum, it->second);
Changed = true;
}
}
return Changed;
}
/// The given values are known to be equal in every block
/// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with
/// 'RHS' everywhere in the scope. Returns whether a change was made.
/// If DominatesByEdge is false, then it means that we will propagate the RHS
/// value starting from the end of Root.Start.
bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
bool DominatesByEdge) {
SmallVector<std::pair<Value*, Value*>, 4> Worklist;
Worklist.push_back(std::make_pair(LHS, RHS));
bool Changed = false;
// For speed, compute a conservative fast approximation to
// DT->dominates(Root, Root.getEnd());
const bool RootDominatesEnd = isOnlyReachableViaThisEdge(Root, DT);
while (!Worklist.empty()) {
std::pair<Value*, Value*> Item = Worklist.pop_back_val();
LHS = Item.first; RHS = Item.second;
if (LHS == RHS)
continue;
assert(LHS->getType() == RHS->getType() && "Equality but unequal types!");
// Don't try to propagate equalities between constants.
if (isa<Constant>(LHS) && isa<Constant>(RHS))
continue;
// Prefer a constant on the right-hand side, or an Argument if no constants.
if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS)))
std::swap(LHS, RHS);
assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!");
// If there is no obvious reason to prefer the left-hand side over the
// right-hand side, ensure the longest lived term is on the right-hand side,
// so the shortest lived term will be replaced by the longest lived.
// This tends to expose more simplifications.
uint32_t LVN = VN.lookupOrAdd(LHS);
if ((isa<Argument>(LHS) && isa<Argument>(RHS)) ||
(isa<Instruction>(LHS) && isa<Instruction>(RHS))) {
// Move the 'oldest' value to the right-hand side, using the value number
// as a proxy for age.
uint32_t RVN = VN.lookupOrAdd(RHS);
if (LVN < RVN) {
std::swap(LHS, RHS);
LVN = RVN;
}
}
// If value numbering later sees that an instruction in the scope is equal
// to 'LHS' then ensure it will be turned into 'RHS'. In order to preserve
// the invariant that instructions only occur in the leader table for their
// own value number (this is used by removeFromLeaderTable), do not do this
// if RHS is an instruction (if an instruction in the scope is morphed into
// LHS then it will be turned into RHS by the next GVN iteration anyway, so
// using the leader table is about compiling faster, not optimizing better).
// The leader table only tracks basic blocks, not edges. Only add to if we
// have the simple case where the edge dominates the end.
if (RootDominatesEnd && !isa<Instruction>(RHS))
addToLeaderTable(LVN, RHS, Root.getEnd());
// Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As
// LHS always has at least one use that is not dominated by Root, this will
// never do anything if LHS has only one use.
if (!LHS->hasOneUse()) {
unsigned NumReplacements =
DominatesByEdge
? replaceDominatedUsesWith(LHS, RHS, *DT, Root)
: replaceDominatedUsesWith(LHS, RHS, *DT, Root.getStart());
Changed |= NumReplacements > 0;
NumGVNEqProp += NumReplacements;
}
// Now try to deduce additional equalities from this one. For example, if
// the known equality was "(A != B)" == "false" then it follows that A and B
// are equal in the scope. Only boolean equalities with an explicit true or
// false RHS are currently supported.
if (!RHS->getType()->isIntegerTy(1))
// Not a boolean equality - bail out.
continue;
ConstantInt *CI = dyn_cast<ConstantInt>(RHS);
if (!CI)
// RHS neither 'true' nor 'false' - bail out.
continue;
// Whether RHS equals 'true'. Otherwise it equals 'false'.
bool isKnownTrue = CI->isMinusOne();
bool isKnownFalse = !isKnownTrue;
// If "A && B" is known true then both A and B are known true. If "A || B"
// is known false then both A and B are known false.
Value *A, *B;
if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) ||
(isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) {
Worklist.push_back(std::make_pair(A, RHS));
Worklist.push_back(std::make_pair(B, RHS));
continue;
}
// If we are propagating an equality like "(A == B)" == "true" then also
// propagate the equality A == B. When propagating a comparison such as
// "(A >= B)" == "true", replace all instances of "A < B" with "false".
if (CmpInst *Cmp = dyn_cast<CmpInst>(LHS)) {
Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1);
// If "A == B" is known true, or "A != B" is known false, then replace
// A with B everywhere in the scope.
if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) ||
(isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE))
Worklist.push_back(std::make_pair(Op0, Op1));
// Handle the floating point versions of equality comparisons too.
if ((isKnownTrue && Cmp->getPredicate() == CmpInst::FCMP_OEQ) ||
(isKnownFalse && Cmp->getPredicate() == CmpInst::FCMP_UNE)) {
// Floating point -0.0 and 0.0 compare equal, so we can only
// propagate values if we know that we have a constant and that
// its value is non-zero.
// FIXME: We should do this optimization if 'no signed zeros' is
// applicable via an instruction-level fast-math-flag or some other
// indicator that relaxed FP semantics are being used.
if (isa<ConstantFP>(Op1) && !cast<ConstantFP>(Op1)->isZero())
Worklist.push_back(std::make_pair(Op0, Op1));
}
// If "A >= B" is known true, replace "A < B" with false everywhere.
CmpInst::Predicate NotPred = Cmp->getInversePredicate();
Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse);
// Since we don't have the instruction "A < B" immediately to hand, work
// out the value number that it would have and use that to find an
// appropriate instruction (if any).
uint32_t NextNum = VN.getNextUnusedValueNumber();
uint32_t Num = VN.lookupOrAddCmp(Cmp->getOpcode(), NotPred, Op0, Op1);
// If the number we were assigned was brand new then there is no point in
// looking for an instruction realizing it: there cannot be one!
if (Num < NextNum) {
Value *NotCmp = findLeader(Root.getEnd(), Num);
if (NotCmp && isa<Instruction>(NotCmp)) {
unsigned NumReplacements =
DominatesByEdge
? replaceDominatedUsesWith(NotCmp, NotVal, *DT, Root)
: replaceDominatedUsesWith(NotCmp, NotVal, *DT,
Root.getStart());
Changed |= NumReplacements > 0;
NumGVNEqProp += NumReplacements;
}
}
// Ensure that any instruction in scope that gets the "A < B" value number
// is replaced with false.
// The leader table only tracks basic blocks, not edges. Only add to if we
// have the simple case where the edge dominates the end.
if (RootDominatesEnd)
addToLeaderTable(Num, NotVal, Root.getEnd());
continue;
}
}
return Changed;
}
/// When calculating availability, handle an instruction
/// by inserting it into the appropriate sets
bool GVN::processInstruction(Instruction *I) {
// Ignore dbg info intrinsics.
if (isa<DbgInfoIntrinsic>(I))
return false;
// If the instruction can be easily simplified then do so now in preference
// to value numbering it. Value numbering often exposes redundancies, for
// example if it determines that %y is equal to %x then the instruction
// "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify.
const DataLayout &DL = I->getModule()->getDataLayout();
if (Value *V = SimplifyInstruction(I, {DL, TLI, DT, AC})) {
bool Changed = false;
if (!I->use_empty()) {
I->replaceAllUsesWith(V);
Changed = true;
}
if (isInstructionTriviallyDead(I, TLI)) {
markInstructionForDeletion(I);
Changed = true;
}
if (Changed) {
if (MD && V->getType()->isPtrOrPtrVectorTy())
MD->invalidateCachedPointerInfo(V);
++NumGVNSimpl;
return true;
}
}
if (IntrinsicInst *IntrinsicI = dyn_cast<IntrinsicInst>(I))
if (IntrinsicI->getIntrinsicID() == Intrinsic::assume)
return processAssumeIntrinsic(IntrinsicI);
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
if (processLoad(LI))
return true;
unsigned Num = VN.lookupOrAdd(LI);
addToLeaderTable(Num, LI, LI->getParent());
return false;
}
// For conditional branches, we can perform simple conditional propagation on
// the condition value itself.
if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
if (!BI->isConditional())
return false;
if (isa<Constant>(BI->getCondition()))
return processFoldableCondBr(BI);
Value *BranchCond = BI->getCondition();
BasicBlock *TrueSucc = BI->getSuccessor(0);
BasicBlock *FalseSucc = BI->getSuccessor(1);
// Avoid multiple edges early.
if (TrueSucc == FalseSucc)
return false;
BasicBlock *Parent = BI->getParent();
bool Changed = false;
Value *TrueVal = ConstantInt::getTrue(TrueSucc->getContext());
BasicBlockEdge TrueE(Parent, TrueSucc);
Changed |= propagateEquality(BranchCond, TrueVal, TrueE, true);
Value *FalseVal = ConstantInt::getFalse(FalseSucc->getContext());
BasicBlockEdge FalseE(Parent, FalseSucc);
Changed |= propagateEquality(BranchCond, FalseVal, FalseE, true);
return Changed;
}
// For switches, propagate the case values into the case destinations.
if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
Value *SwitchCond = SI->getCondition();
BasicBlock *Parent = SI->getParent();
bool Changed = false;
// Remember how many outgoing edges there are to every successor.
SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges;
for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i)
++SwitchEdges[SI->getSuccessor(i)];
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
BasicBlock *Dst = i->getCaseSuccessor();
// If there is only a single edge, propagate the case value into it.
if (SwitchEdges.lookup(Dst) == 1) {
BasicBlockEdge E(Parent, Dst);
Changed |= propagateEquality(SwitchCond, i->getCaseValue(), E, true);
}
}
return Changed;
}
// Instructions with void type don't return a value, so there's
// no point in trying to find redundancies in them.
if (I->getType()->isVoidTy())
return false;
uint32_t NextNum = VN.getNextUnusedValueNumber();
unsigned Num = VN.lookupOrAdd(I);
// Allocations are always uniquely numbered, so we can save time and memory
// by fast failing them.
if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) {
addToLeaderTable(Num, I, I->getParent());
return false;
}
// If the number we were assigned was a brand new VN, then we don't
// need to do a lookup to see if the number already exists
// somewhere in the domtree: it can't!
if (Num >= NextNum) {
addToLeaderTable(Num, I, I->getParent());
return false;
}
// Perform fast-path value-number based elimination of values inherited from
// dominators.
Value *Repl = findLeader(I->getParent(), Num);
if (!Repl) {
// Failure, just remember this instance for future use.
addToLeaderTable(Num, I, I->getParent());
return false;
} else if (Repl == I) {
// If I was the result of a shortcut PRE, it might already be in the table
// and the best replacement for itself. Nothing to do.
return false;
}
// Remove it!
patchAndReplaceAllUsesWith(I, Repl);
if (MD && Repl->getType()->isPtrOrPtrVectorTy())
MD->invalidateCachedPointerInfo(Repl);
markInstructionForDeletion(I);
return true;
}
/// runOnFunction - This is the main transformation entry point for a function.
bool GVN::runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT,
const TargetLibraryInfo &RunTLI, AAResults &RunAA,
MemoryDependenceResults *RunMD, LoopInfo *LI,
OptimizationRemarkEmitter *RunORE) {
AC = &RunAC;
DT = &RunDT;
VN.setDomTree(DT);
TLI = &RunTLI;
VN.setAliasAnalysis(&RunAA);
MD = RunMD;
VN.setMemDep(MD);
ORE = RunORE;
bool Changed = false;
bool ShouldContinue = true;
// Merge unconditional branches, allowing PRE to catch more
// optimization opportunities.
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
BasicBlock *BB = &*FI++;
bool removedBlock = MergeBlockIntoPredecessor(BB, DT, LI, MD);
if (removedBlock)
++NumGVNBlocks;
Changed |= removedBlock;
}
unsigned Iteration = 0;
while (ShouldContinue) {
DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
ShouldContinue = iterateOnFunction(F);
Changed |= ShouldContinue;
++Iteration;
}
if (EnablePRE) {
// Fabricate val-num for dead-code in order to suppress assertion in
// performPRE().
assignValNumForDeadCode();
assignBlockRPONumber(F);
bool PREChanged = true;
while (PREChanged) {
PREChanged = performPRE(F);
Changed |= PREChanged;
}
}
// FIXME: Should perform GVN again after PRE does something. PRE can move
// computations into blocks where they become fully redundant. Note that
// we can't do this until PRE's critical edge splitting updates memdep.
// Actually, when this happens, we should just fully integrate PRE into GVN.
cleanupGlobalSets();
// Do not cleanup DeadBlocks in cleanupGlobalSets() as it's called for each
// iteration.
DeadBlocks.clear();
return Changed;
}
bool GVN::processBlock(BasicBlock *BB) {
// FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function
// (and incrementing BI before processing an instruction).
assert(InstrsToErase.empty() &&
"We expect InstrsToErase to be empty across iterations");
if (DeadBlocks.count(BB))
return false;
// Clearing map before every BB because it can be used only for single BB.
ReplaceWithConstMap.clear();
bool ChangedFunction = false;
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE;) {
if (!ReplaceWithConstMap.empty())
ChangedFunction |= replaceOperandsWithConsts(&*BI);
ChangedFunction |= processInstruction(&*BI);
if (InstrsToErase.empty()) {
++BI;
continue;
}
// If we need some instructions deleted, do it now.
NumGVNInstr += InstrsToErase.size();
// Avoid iterator invalidation.
bool AtStart = BI == BB->begin();
if (!AtStart)
--BI;
for (SmallVectorImpl<Instruction *>::iterator I = InstrsToErase.begin(),
E = InstrsToErase.end(); I != E; ++I) {
DEBUG(dbgs() << "GVN removed: " << **I << '\n');
if (MD) MD->removeInstruction(*I);
DEBUG(verifyRemoved(*I));
(*I)->eraseFromParent();
}
InstrsToErase.clear();
if (AtStart)
BI = BB->begin();
else
++BI;
}
return ChangedFunction;
}
// Instantiate an expression in a predecessor that lacked it.
bool GVN::performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred,
BasicBlock *Curr, unsigned int ValNo) {
// Because we are going top-down through the block, all value numbers
// will be available in the predecessor by the time we need them. Any
// that weren't originally present will have been instantiated earlier
// in this loop.
bool success = true;
for (unsigned i = 0, e = Instr->getNumOperands(); i != e; ++i) {
Value *Op = Instr->getOperand(i);
if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
continue;
// This could be a newly inserted instruction, in which case, we won't
// find a value number, and should give up before we hurt ourselves.
// FIXME: Rewrite the infrastructure to let it easier to value number
// and process newly inserted instructions.
if (!VN.exists(Op)) {
success = false;
break;
}
uint32_t TValNo =
VN.phiTranslate(Pred, Curr, VN.lookup(Op), *this);
if (Value *V = findLeader(Pred, TValNo)) {
Instr->setOperand(i, V);
} else {
success = false;
break;
}
}
// Fail out if we encounter an operand that is not available in
// the PRE predecessor. This is typically because of loads which
// are not value numbered precisely.
if (!success)
return false;
Instr->insertBefore(Pred->getTerminator());
Instr->setName(Instr->getName() + ".pre");
Instr->setDebugLoc(Instr->getDebugLoc());
unsigned Num = VN.lookupOrAdd(Instr);
VN.add(Instr, Num);
// Update the availability map to include the new instruction.
addToLeaderTable(Num, Instr, Pred);
return true;
}
bool GVN::performScalarPRE(Instruction *CurInst) {
if (isa<AllocaInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
isa<PHINode>(CurInst) || CurInst->getType()->isVoidTy() ||
CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
isa<DbgInfoIntrinsic>(CurInst))
return false;
// Don't do PRE on compares. The PHI would prevent CodeGenPrepare from
// sinking the compare again, and it would force the code generator to
// move the i1 from processor flags or predicate registers into a general
// purpose register.
if (isa<CmpInst>(CurInst))
return false;
// We don't currently value number ANY inline asm calls.
if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
if (CallI->isInlineAsm())
return false;
uint32_t ValNo = VN.lookup(CurInst);
// Look for the predecessors for PRE opportunities. We're
// only trying to solve the basic diamond case, where
// a value is computed in the successor and one predecessor,
// but not the other. We also explicitly disallow cases
// where the successor is its own predecessor, because they're
// more complicated to get right.
unsigned NumWith = 0;
unsigned NumWithout = 0;
BasicBlock *PREPred = nullptr;
BasicBlock *CurrentBlock = CurInst->getParent();
SmallVector<std::pair<Value *, BasicBlock *>, 8> predMap;
for (BasicBlock *P : predecessors(CurrentBlock)) {
// We're not interested in PRE where blocks with predecessors that are
// not reachable.
if (!DT->isReachableFromEntry(P)) {
NumWithout = 2;
break;
}
// It is not safe to do PRE when P->CurrentBlock is a loop backedge, and
// when CurInst has operand defined in CurrentBlock (so it may be defined
// by phi in the loop header).
if (BlockRPONumber[P] >= BlockRPONumber[CurrentBlock] &&
any_of(CurInst->operands(), [&](const Use &U) {
if (auto *Inst = dyn_cast<Instruction>(U.get()))
return Inst->getParent() == CurrentBlock;
return false;
})) {
NumWithout = 2;
break;
}
uint32_t TValNo = VN.phiTranslate(P, CurrentBlock, ValNo, *this);
Value *predV = findLeader(P, TValNo);
if (!predV) {
predMap.push_back(std::make_pair(static_cast<Value *>(nullptr), P));
PREPred = P;
++NumWithout;
} else if (predV == CurInst) {
/* CurInst dominates this predecessor. */
NumWithout = 2;
break;
} else {
predMap.push_back(std::make_pair(predV, P));
++NumWith;
}
}
// Don't do PRE when it might increase code size, i.e. when
// we would need to insert instructions in more than one pred.
if (NumWithout > 1 || NumWith == 0)
return false;
// We may have a case where all predecessors have the instruction,
// and we just need to insert a phi node. Otherwise, perform
// insertion.
Instruction *PREInstr = nullptr;
if (NumWithout != 0) {
// Don't do PRE across indirect branch.
if (isa<IndirectBrInst>(PREPred->getTerminator()))
return false;
// We can't do PRE safely on a critical edge, so instead we schedule
// the edge to be split and perform the PRE the next time we iterate
// on the function.
unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
return false;
}
// We need to insert somewhere, so let's give it a shot
PREInstr = CurInst->clone();
if (!performScalarPREInsertion(PREInstr, PREPred, CurrentBlock, ValNo)) {
// If we failed insertion, make sure we remove the instruction.
DEBUG(verifyRemoved(PREInstr));
PREInstr->deleteValue();
return false;
}
}
// Either we should have filled in the PRE instruction, or we should
// not have needed insertions.
assert (PREInstr != nullptr || NumWithout == 0);
++NumGVNPRE;
// Create a PHI to make the value available in this block.
PHINode *Phi =
PHINode::Create(CurInst->getType(), predMap.size(),
CurInst->getName() + ".pre-phi", &CurrentBlock->front());
for (unsigned i = 0, e = predMap.size(); i != e; ++i) {
if (Value *V = predMap[i].first)
Phi->addIncoming(V, predMap[i].second);
else
Phi->addIncoming(PREInstr, PREPred);
}
VN.add(Phi, ValNo);
addToLeaderTable(ValNo, Phi, CurrentBlock);
Phi->setDebugLoc(CurInst->getDebugLoc());
CurInst->replaceAllUsesWith(Phi);
if (MD && Phi->getType()->isPtrOrPtrVectorTy())
MD->invalidateCachedPointerInfo(Phi);
VN.erase(CurInst);
removeFromLeaderTable(ValNo, CurInst, CurrentBlock);
DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
if (MD)
MD->removeInstruction(CurInst);
DEBUG(verifyRemoved(CurInst));
CurInst->eraseFromParent();
++NumGVNInstr;
return true;
}
/// Perform a purely local form of PRE that looks for diamond
/// control flow patterns and attempts to perform simple PRE at the join point.
bool GVN::performPRE(Function &F) {
bool Changed = false;
for (BasicBlock *CurrentBlock : depth_first(&F.getEntryBlock())) {
// Nothing to PRE in the entry block.
if (CurrentBlock == &F.getEntryBlock())
continue;
// Don't perform PRE on an EH pad.
if (CurrentBlock->isEHPad())
continue;
for (BasicBlock::iterator BI = CurrentBlock->begin(),
BE = CurrentBlock->end();
BI != BE;) {
Instruction *CurInst = &*BI++;
Changed |= performScalarPRE(CurInst);
}
}
if (splitCriticalEdges())
Changed = true;
return Changed;
}
/// Split the critical edge connecting the given two blocks, and return
/// the block inserted to the critical edge.
BasicBlock *GVN::splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ) {
BasicBlock *BB =
SplitCriticalEdge(Pred, Succ, CriticalEdgeSplittingOptions(DT));
if (MD)
MD->invalidateCachedPredecessors();
return BB;
}
/// Split critical edges found during the previous
/// iteration that may enable further optimization.
bool GVN::splitCriticalEdges() {
if (toSplit.empty())
return false;
do {
std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
SplitCriticalEdge(Edge.first, Edge.second,
CriticalEdgeSplittingOptions(DT));
} while (!toSplit.empty());
if (MD) MD->invalidateCachedPredecessors();
return true;
}
/// Executes one iteration of GVN
bool GVN::iterateOnFunction(Function &F) {
cleanupGlobalSets();
// Top-down walk of the dominator tree
bool Changed = false;
// Needed for value numbering with phi construction to work.
// RPOT walks the graph in its constructor and will not be invalidated during
// processBlock.
ReversePostOrderTraversal<Function *> RPOT(&F);
for (BasicBlock *BB : RPOT)
Changed |= processBlock(BB);
return Changed;
}
void GVN::cleanupGlobalSets() {
VN.clear();
LeaderTable.clear();
BlockRPONumber.clear();
TableAllocator.Reset();
}
/// Verify that the specified instruction does not occur in our
/// internal data structures.
void GVN::verifyRemoved(const Instruction *Inst) const {
VN.verifyRemoved(Inst);
// Walk through the value number scope to make sure the instruction isn't
// ferreted away in it.
for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator
I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) {
const LeaderTableEntry *Node = &I->second;
assert(Node->Val != Inst && "Inst still in value numbering scope!");
while (Node->Next) {
Node = Node->Next;
assert(Node->Val != Inst && "Inst still in value numbering scope!");
}
}
}
/// BB is declared dead, which implied other blocks become dead as well. This
/// function is to add all these blocks to "DeadBlocks". For the dead blocks'
/// live successors, update their phi nodes by replacing the operands
/// corresponding to dead blocks with UndefVal.
void GVN::addDeadBlock(BasicBlock *BB) {
SmallVector<BasicBlock *, 4> NewDead;
SmallSetVector<BasicBlock *, 4> DF;
NewDead.push_back(BB);
while (!NewDead.empty()) {
BasicBlock *D = NewDead.pop_back_val();
if (DeadBlocks.count(D))
continue;
// All blocks dominated by D are dead.
SmallVector<BasicBlock *, 8> Dom;
DT->getDescendants(D, Dom);
DeadBlocks.insert(Dom.begin(), Dom.end());
// Figure out the dominance-frontier(D).
for (BasicBlock *B : Dom) {
for (BasicBlock *S : successors(B)) {
if (DeadBlocks.count(S))
continue;
bool AllPredDead = true;
for (BasicBlock *P : predecessors(S))
if (!DeadBlocks.count(P)) {
AllPredDead = false;
break;
}
if (!AllPredDead) {
// S could be proved dead later on. That is why we don't update phi
// operands at this moment.
DF.insert(S);
} else {
// While S is not dominated by D, it is dead by now. This could take
// place if S already have a dead predecessor before D is declared
// dead.
NewDead.push_back(S);
}
}
}
}
// For the dead blocks' live successors, update their phi nodes by replacing
// the operands corresponding to dead blocks with UndefVal.
for(SmallSetVector<BasicBlock *, 4>::iterator I = DF.begin(), E = DF.end();
I != E; I++) {
BasicBlock *B = *I;
if (DeadBlocks.count(B))
continue;
SmallVector<BasicBlock *, 4> Preds(pred_begin(B), pred_end(B));
for (BasicBlock *P : Preds) {
if (!DeadBlocks.count(P))
continue;
if (isCriticalEdge(P->getTerminator(), GetSuccessorNumber(P, B))) {
if (BasicBlock *S = splitCriticalEdges(P, B))
DeadBlocks.insert(P = S);
}
for (BasicBlock::iterator II = B->begin(); isa<PHINode>(II); ++II) {
PHINode &Phi = cast<PHINode>(*II);
Phi.setIncomingValue(Phi.getBasicBlockIndex(P),
UndefValue::get(Phi.getType()));
}
}
}
}
// If the given branch is recognized as a foldable branch (i.e. conditional
// branch with constant condition), it will perform following analyses and
// transformation.
// 1) If the dead out-coming edge is a critical-edge, split it. Let
// R be the target of the dead out-coming edge.
// 1) Identify the set of dead blocks implied by the branch's dead outcoming
// edge. The result of this step will be {X| X is dominated by R}
// 2) Identify those blocks which haves at least one dead predecessor. The
// result of this step will be dominance-frontier(R).
// 3) Update the PHIs in DF(R) by replacing the operands corresponding to
// dead blocks with "UndefVal" in an hope these PHIs will optimized away.
//
// Return true iff *NEW* dead code are found.
bool GVN::processFoldableCondBr(BranchInst *BI) {
if (!BI || BI->isUnconditional())
return false;
// If a branch has two identical successors, we cannot declare either dead.
if (BI->getSuccessor(0) == BI->getSuccessor(1))
return false;
ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition());
if (!Cond)
return false;
BasicBlock *DeadRoot =
Cond->getZExtValue() ? BI->getSuccessor(1) : BI->getSuccessor(0);
if (DeadBlocks.count(DeadRoot))
return false;
if (!DeadRoot->getSinglePredecessor())
DeadRoot = splitCriticalEdges(BI->getParent(), DeadRoot);
addDeadBlock(DeadRoot);
return true;
}
// performPRE() will trigger assert if it comes across an instruction without
// associated val-num. As it normally has far more live instructions than dead
// instructions, it makes more sense just to "fabricate" a val-number for the
// dead code than checking if instruction involved is dead or not.
void GVN::assignValNumForDeadCode() {
for (BasicBlock *BB : DeadBlocks) {
for (Instruction &Inst : *BB) {
unsigned ValNum = VN.lookupOrAdd(&Inst);
addToLeaderTable(ValNum, &Inst, BB);
}
}
}
class llvm::gvn::GVNLegacyPass : public FunctionPass {
public:
static char ID; // Pass identification, replacement for typeid
explicit GVNLegacyPass(bool NoLoads = false)
: FunctionPass(ID), NoLoads(NoLoads) {
initializeGVNLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
return Impl.runImpl(
F, getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F),
getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
getAnalysis<AAResultsWrapperPass>().getAAResults(),
NoLoads ? nullptr
: &getAnalysis<MemoryDependenceWrapperPass>().getMemDep(),
LIWP ? &LIWP->getLoopInfo() : nullptr,
&getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
if (!NoLoads)
AU.addRequired<MemoryDependenceWrapperPass>();
AU.addRequired<AAResultsWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addPreserved<TargetLibraryInfoWrapperPass>();
AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
}
private:
bool NoLoads;
GVN Impl;
};
char GVNLegacyPass::ID = 0;
// The public interface to this file...
FunctionPass *llvm::createGVNPass(bool NoLoads) {
return new GVNLegacyPass(NoLoads);
}
INITIALIZE_PASS_BEGIN(GVNLegacyPass, "gvn", "Global Value Numbering", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
INITIALIZE_PASS_END(GVNLegacyPass, "gvn", "Global Value Numbering", false, false)
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