#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include "llvm/IR/IRBuilder.h"
"disable-separate-const-offset-from-gep", cl::init(false),
cl::desc("Do not separate the constant offset from a GEP instruction"),
cl::Hidden);
+// Setting this flag may emit false positives when the input module already
+// contains dead instructions. Therefore, we set it only in unit tests that are
+// free of dead code.
+static cl::opt<bool>
+ VerifyNoDeadCode("reassociate-geps-verify-no-dead-code", cl::init(false),
+ cl::desc("Verify this pass produces no dead code"),
+ cl::Hidden);
namespace {
/// 5); nor can we transform (3 * (a + 5)) to (3 * a + 5), however in this case,
/// -instcombine probably already optimized (3 * (a + 5)) to (3 * a + 15).
class ConstantOffsetExtractor {
- public:
+public:
/// Extracts a constant offset from the given GEP index. It returns the
/// new index representing the remainder (equal to the original index minus
/// the constant offset), or nullptr if we cannot extract a constant offset.
- /// \p Idx The given GEP index
- /// \p DL The datalayout of the module
- /// \p GEP The given GEP
- static Value *Extract(Value *Idx, const DataLayout *DL,
- GetElementPtrInst *GEP);
+ /// \p Idx The given GEP index
+ /// \p GEP The given GEP
+ /// \p UserChainTail Outputs the tail of UserChain so that we can
+ /// garbage-collect unused instructions in UserChain.
+ static Value *Extract(Value *Idx, GetElementPtrInst *GEP,
+ User *&UserChainTail, const DominatorTree *DT);
/// Looks for a constant offset from the given GEP index without extracting
/// it. It returns the numeric value of the extracted constant offset (0 if
/// failed). The meaning of the arguments are the same as Extract.
- static int64_t Find(Value *Idx, const DataLayout *DL, GetElementPtrInst *GEP);
+ static int64_t Find(Value *Idx, GetElementPtrInst *GEP,
+ const DominatorTree *DT);
- private:
- ConstantOffsetExtractor(const DataLayout *Layout, Instruction *InsertionPt)
- : DL(Layout), IP(InsertionPt) {}
+private:
+ ConstantOffsetExtractor(Instruction *InsertionPt, const DominatorTree *DT)
+ : IP(InsertionPt), DL(InsertionPt->getModule()->getDataLayout()), DT(DT) {
+ }
/// Searches the expression that computes V for a non-zero constant C s.t.
/// V can be reassociated into the form V' + C. If the searching is
/// successful, returns C and update UserChain as a def-use chain from C to V;
/// returns "sext i32 (zext i16 V to i32) to i64".
Value *applyExts(Value *V);
- /// Returns true if LHS and RHS have no bits in common, i.e., LHS | RHS == 0.
- bool NoCommonBits(Value *LHS, Value *RHS) const;
- /// Computes which bits are known to be one or zero.
- /// \p KnownOne Mask of all bits that are known to be one.
- /// \p KnownZero Mask of all bits that are known to be zero.
- void ComputeKnownBits(Value *V, APInt &KnownOne, APInt &KnownZero) const;
/// A helper function that returns whether we can trace into the operands
/// of binary operator BO for a constant offset.
///
/// A data structure used in rebuildWithoutConstOffset. Contains all
/// sext/zext instructions along UserChain.
SmallVector<CastInst *, 16> ExtInsts;
- /// The data layout of the module. Used in ComputeKnownBits.
- const DataLayout *DL;
Instruction *IP; /// Insertion position of cloned instructions.
+ const DataLayout &DL;
+ const DominatorTree *DT;
};
/// \brief A pass that tries to split every GEP in the function into a variadic
/// base and a constant offset. It is a FunctionPass because searching for the
/// constant offset may inspect other basic blocks.
class SeparateConstOffsetFromGEP : public FunctionPass {
- public:
+public:
static char ID;
SeparateConstOffsetFromGEP(const TargetMachine *TM = nullptr,
bool LowerGEP = false)
- : FunctionPass(ID), TM(TM), LowerGEP(LowerGEP) {
+ : FunctionPass(ID), DL(nullptr), DT(nullptr), TM(TM), LowerGEP(LowerGEP) {
initializeSeparateConstOffsetFromGEPPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
- AU.addRequired<DataLayoutPass>();
+ AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.setPreservesCFG();
}
bool doInitialization(Module &M) override {
- DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
- if (DLP == nullptr)
- report_fatal_error("data layout missing");
- DL = &DLP->getDataLayout();
+ DL = &M.getDataLayout();
return false;
}
-
bool runOnFunction(Function &F) override;
- private:
+private:
/// Tries to split the given GEP into a variadic base and a constant offset,
/// and returns true if the splitting succeeds.
bool splitGEP(GetElementPtrInst *GEP);
///
/// Verified in @i32_add in split-gep.ll
bool canonicalizeArrayIndicesToPointerSize(GetElementPtrInst *GEP);
+ /// Verify F is free of dead code.
+ void verifyNoDeadCode(Function &F);
const DataLayout *DL;
+ const DominatorTree *DT;
const TargetMachine *TM;
/// Whether to lower a GEP with multiple indices into arithmetic operations or
/// multiple GEPs with a single index.
SeparateConstOffsetFromGEP, "separate-const-offset-from-gep",
"Split GEPs to a variadic base and a constant offset for better CSE", false,
false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(DataLayoutPass)
INITIALIZE_PASS_END(
SeparateConstOffsetFromGEP, "separate-const-offset-from-gep",
"Split GEPs to a variadic base and a constant offset for better CSE", false,
Value *LHS = BO->getOperand(0), *RHS = BO->getOperand(1);
// Do not trace into "or" unless it is equivalent to "add". If LHS and RHS
// don't have common bits, (LHS | RHS) is equivalent to (LHS + RHS).
- if (BO->getOpcode() == Instruction::Or && !NoCommonBits(LHS, RHS))
+ if (BO->getOpcode() == Instruction::Or &&
+ !haveNoCommonBitsSet(LHS, RHS, DL, nullptr, BO, DT))
return false;
// In addition, tracing into BO requires that its surrounding s/zext (if
ConstantOffset = CI->getValue();
} else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V)) {
// Trace into subexpressions for more hoisting opportunities.
- if (CanTraceInto(SignExtended, ZeroExtended, BO, NonNegative)) {
+ if (CanTraceInto(SignExtended, ZeroExtended, BO, NonNegative))
ConstantOffset = findInEitherOperand(BO, SignExtended, ZeroExtended);
- }
} else if (isa<SExtInst>(V)) {
ConstantOffset = find(U->getOperand(0), /* SignExtended */ true,
ZeroExtended, NonNegative).sext(BitWidth);
}
BinaryOperator *BO = cast<BinaryOperator>(UserChain[ChainIndex]);
+ assert(BO->getNumUses() <= 1 &&
+ "distributeExtsAndCloneChain clones each BinaryOperator in "
+ "UserChain, so no one should be used more than "
+ "once");
+
unsigned OpNo = (BO->getOperand(0) == UserChain[ChainIndex - 1] ? 0 : 1);
assert(BO->getOperand(OpNo) == UserChain[ChainIndex - 1]);
Value *NextInChain = removeConstOffset(ChainIndex - 1);
return TheOther;
}
+ BinaryOperator::BinaryOps NewOp = BO->getOpcode();
if (BO->getOpcode() == Instruction::Or) {
// Rebuild "or" as "add", because "or" may be invalid for the new
// epxression.
//
// Replacing the "or" with "add" is fine, because
// a | (b + 5) = a + (b + 5) = (a + b) + 5
- if (OpNo == 0) {
- return BinaryOperator::CreateAdd(NextInChain, TheOther, BO->getName(),
- IP);
- } else {
- return BinaryOperator::CreateAdd(TheOther, NextInChain, BO->getName(),
- IP);
- }
+ NewOp = Instruction::Add;
}
- // We can reuse BO in this case, because the new expression shares the same
- // instruction type and BO is used at most once.
- assert(BO->getNumUses() <= 1 &&
- "distributeExtsAndCloneChain clones each BinaryOperator in "
- "UserChain, so no one should be used more than "
- "once");
- BO->setOperand(OpNo, NextInChain);
- BO->setHasNoSignedWrap(false);
- BO->setHasNoUnsignedWrap(false);
- // Make sure it appears after all instructions we've inserted so far.
- BO->moveBefore(IP);
- return BO;
+ BinaryOperator *NewBO;
+ if (OpNo == 0) {
+ NewBO = BinaryOperator::Create(NewOp, NextInChain, TheOther, "", IP);
+ } else {
+ NewBO = BinaryOperator::Create(NewOp, TheOther, NextInChain, "", IP);
+ }
+ NewBO->takeName(BO);
+ return NewBO;
}
-Value *ConstantOffsetExtractor::Extract(Value *Idx, const DataLayout *DL,
- GetElementPtrInst *GEP) {
- ConstantOffsetExtractor Extractor(DL, GEP);
+Value *ConstantOffsetExtractor::Extract(Value *Idx, GetElementPtrInst *GEP,
+ User *&UserChainTail,
+ const DominatorTree *DT) {
+ ConstantOffsetExtractor Extractor(GEP, DT);
// Find a non-zero constant offset first.
APInt ConstantOffset =
Extractor.find(Idx, /* SignExtended */ false, /* ZeroExtended */ false,
GEP->isInBounds());
- if (ConstantOffset == 0)
+ if (ConstantOffset == 0) {
+ UserChainTail = nullptr;
return nullptr;
+ }
// Separates the constant offset from the GEP index.
- return Extractor.rebuildWithoutConstOffset();
+ Value *IdxWithoutConstOffset = Extractor.rebuildWithoutConstOffset();
+ UserChainTail = Extractor.UserChain.back();
+ return IdxWithoutConstOffset;
}
-int64_t ConstantOffsetExtractor::Find(Value *Idx, const DataLayout *DL,
- GetElementPtrInst *GEP) {
+int64_t ConstantOffsetExtractor::Find(Value *Idx, GetElementPtrInst *GEP,
+ const DominatorTree *DT) {
// If Idx is an index of an inbound GEP, Idx is guaranteed to be non-negative.
- return ConstantOffsetExtractor(DL, GEP)
+ return ConstantOffsetExtractor(GEP, DT)
.find(Idx, /* SignExtended */ false, /* ZeroExtended */ false,
GEP->isInBounds())
.getSExtValue();
}
-void ConstantOffsetExtractor::ComputeKnownBits(Value *V, APInt &KnownOne,
- APInt &KnownZero) const {
- IntegerType *IT = cast<IntegerType>(V->getType());
- KnownOne = APInt(IT->getBitWidth(), 0);
- KnownZero = APInt(IT->getBitWidth(), 0);
- llvm::computeKnownBits(V, KnownZero, KnownOne, DL, 0);
-}
-
-bool ConstantOffsetExtractor::NoCommonBits(Value *LHS, Value *RHS) const {
- assert(LHS->getType() == RHS->getType() &&
- "LHS and RHS should have the same type");
- APInt LHSKnownOne, LHSKnownZero, RHSKnownOne, RHSKnownZero;
- ComputeKnownBits(LHS, LHSKnownOne, LHSKnownZero);
- ComputeKnownBits(RHS, RHSKnownOne, RHSKnownZero);
- return (LHSKnownZero | RHSKnownZero).isAllOnesValue();
-}
-
bool SeparateConstOffsetFromGEP::canonicalizeArrayIndicesToPointerSize(
GetElementPtrInst *GEP) {
bool Changed = false;
if (isa<SequentialType>(*GTI)) {
// Tries to extract a constant offset from this GEP index.
int64_t ConstantOffset =
- ConstantOffsetExtractor::Find(GEP->getOperand(I), DL, GEP);
+ ConstantOffsetExtractor::Find(GEP->getOperand(I), GEP, DT);
if (ConstantOffset != 0) {
NeedsExtraction = true;
// A GEP may have multiple indices. We accumulate the extracted
}
}
// Create an ugly GEP with a single index for each index.
- ResultPtr = Builder.CreateGEP(ResultPtr, Idx, "uglygep");
+ ResultPtr =
+ Builder.CreateGEP(Builder.getInt8Ty(), ResultPtr, Idx, "uglygep");
}
}
// Create a GEP with the constant offset index.
if (AccumulativeByteOffset != 0) {
Value *Offset = ConstantInt::get(IntPtrTy, AccumulativeByteOffset);
- ResultPtr = Builder.CreateGEP(ResultPtr, Offset, "uglygep");
+ ResultPtr =
+ Builder.CreateGEP(Builder.getInt8Ty(), ResultPtr, Offset, "uglygep");
}
if (ResultPtr->getType() != Variadic->getType())
ResultPtr = Builder.CreateBitCast(ResultPtr, Variadic->getType());
TargetTransformInfo &TTI =
getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
*GEP->getParent()->getParent());
+ unsigned AddrSpace = GEP->getPointerAddressSpace();
if (!TTI.isLegalAddressingMode(GEP->getType()->getElementType(),
/*BaseGV=*/nullptr, AccumulativeByteOffset,
- /*HasBaseReg=*/true, /*Scale=*/0)) {
+ /*HasBaseReg=*/true, /*Scale=*/0,
+ AddrSpace)) {
return Changed;
}
}
if (isa<SequentialType>(*GTI)) {
// Splits this GEP index into a variadic part and a constant offset, and
// uses the variadic part as the new index.
+ Value *OldIdx = GEP->getOperand(I);
+ User *UserChainTail;
Value *NewIdx =
- ConstantOffsetExtractor::Extract(GEP->getOperand(I), DL, GEP);
+ ConstantOffsetExtractor::Extract(OldIdx, GEP, UserChainTail, DT);
if (NewIdx != nullptr) {
+ // Switches to the index with the constant offset removed.
GEP->setOperand(I, NewIdx);
+ // After switching to the new index, we can garbage-collect UserChain
+ // and the old index if they are not used.
+ RecursivelyDeleteTriviallyDeadInstructions(UserChainTail);
+ RecursivelyDeleteTriviallyDeadInstructions(OldIdx);
}
}
}
// Very likely. As long as %gep is natually aligned, the byte offset we
// extracted should be a multiple of sizeof(*%gep).
int64_t Index = AccumulativeByteOffset / ElementTypeSizeOfGEP;
- NewGEP = GetElementPtrInst::Create(
- NewGEP, ConstantInt::get(IntPtrTy, Index, true), GEP->getName(), GEP);
+ NewGEP = GetElementPtrInst::Create(GEP->getResultElementType(), NewGEP,
+ ConstantInt::get(IntPtrTy, Index, true),
+ GEP->getName(), GEP);
} else {
// Unlikely but possible. For example,
// #pragma pack(1)
GEP->getPointerAddressSpace());
NewGEP = new BitCastInst(NewGEP, I8PtrTy, "", GEP);
NewGEP = GetElementPtrInst::Create(
- NewGEP, ConstantInt::get(IntPtrTy, AccumulativeByteOffset, true),
- "uglygep", GEP);
+ Type::getInt8Ty(GEP->getContext()), NewGEP,
+ ConstantInt::get(IntPtrTy, AccumulativeByteOffset, true), "uglygep",
+ GEP);
if (GEP->getType() != I8PtrTy)
NewGEP = new BitCastInst(NewGEP, GEP->getType(), GEP->getName(), GEP);
}
if (DisableSeparateConstOffsetFromGEP)
return false;
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+
bool Changed = false;
for (Function::iterator B = F.begin(), BE = F.end(); B != BE; ++B) {
for (BasicBlock::iterator I = B->begin(), IE = B->end(); I != IE; ) {
// already.
}
}
+
+ if (VerifyNoDeadCode)
+ verifyNoDeadCode(F);
+
return Changed;
}
+
+void SeparateConstOffsetFromGEP::verifyNoDeadCode(Function &F) {
+ for (auto &B : F) {
+ for (auto &I : B) {
+ if (isInstructionTriviallyDead(&I)) {
+ std::string ErrMessage;
+ raw_string_ostream RSO(ErrMessage);
+ RSO << "Dead instruction detected!\n" << I << "\n";
+ llvm_unreachable(RSO.str().c_str());
+ }
+ }
+ }
+}
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