//
//===----------------------------------------------------------------------===//
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
+#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Operator.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/IR/IRBuilder.h"
using namespace llvm;
+using namespace llvm::PatternMatch;
static cl::opt<bool> DisableSeparateConstOffsetFromGEP(
"disable-separate-const-offset-from-gep", cl::init(false),
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
+ AU.addRequired<LoopInfoWrapperPass>();
AU.setPreservesCFG();
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
}
bool doInitialization(Module &M) override {
///
/// Verified in @i32_add in split-gep.ll
bool canonicalizeArrayIndicesToPointerSize(GetElementPtrInst *GEP);
+ /// Optimize sext(a)+sext(b) to sext(a+b) when a+b can't sign overflow.
+ /// SeparateConstOffsetFromGEP distributes a sext to leaves before extracting
+ /// the constant offset. After extraction, it becomes desirable to reunion the
+ /// distributed sexts. For example,
+ ///
+ /// &a[sext(i +nsw (j +nsw 5)]
+ /// => distribute &a[sext(i) +nsw (sext(j) +nsw 5)]
+ /// => constant extraction &a[sext(i) + sext(j)] + 5
+ /// => reunion &a[sext(i +nsw j)] + 5
+ bool reuniteExts(Function &F);
+ /// A helper that reunites sexts in an instruction.
+ bool reuniteExts(Instruction *I);
+ /// Find the closest dominator of <Dominatee> that is equivalent to <Key>.
+ Instruction *findClosestMatchingDominator(const SCEV *Key,
+ Instruction *Dominatee);
/// Verify F is free of dead code.
void verifyNoDeadCode(Function &F);
+ bool hasMoreThanOneUseInLoop(Value *v, Loop *L);
+ // Swap the index operand of two GEP.
+ void swapGEPOperand(GetElementPtrInst *First, GetElementPtrInst *Second);
+ // Check if it is safe to swap operand of two GEP.
+ bool isLegalToSwapOperand(GetElementPtrInst *First, GetElementPtrInst *Second,
+ Loop *CurLoop);
+
const DataLayout *DL;
- const DominatorTree *DT;
+ DominatorTree *DT;
+ ScalarEvolution *SE;
const TargetMachine *TM;
+
+ LoopInfo *LI;
+ TargetLibraryInfo *TLI;
/// Whether to lower a GEP with multiple indices into arithmetic operations or
/// multiple GEPs with a single index.
bool LowerGEP;
+ DenseMap<const SCEV *, SmallVector<Instruction *, 2>> DominatingExprs;
};
} // anonymous namespace
"Split GEPs to a variadic base and a constant offset for better CSE", false,
false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(
SeparateConstOffsetFromGEP, "separate-const-offset-from-gep",
"Split GEPs to a variadic base and a constant offset for better CSE", false,
Type *I8PtrTy =
Builder.getInt8PtrTy(Variadic->getType()->getPointerAddressSpace());
Value *ResultPtr = Variadic->getOperand(0);
+ Loop *L = LI->getLoopFor(Variadic->getParent());
+ // Check if the base is not loop invariant or used more than once.
+ bool isSwapCandidate =
+ L && L->isLoopInvariant(ResultPtr) &&
+ !hasMoreThanOneUseInLoop(ResultPtr, L);
+ Value *FirstResult = nullptr;
+
if (ResultPtr->getType() != I8PtrTy)
ResultPtr = Builder.CreateBitCast(ResultPtr, I8PtrTy);
// Create an ugly GEP with a single index for each index.
ResultPtr =
Builder.CreateGEP(Builder.getInt8Ty(), ResultPtr, Idx, "uglygep");
+ if (FirstResult == nullptr)
+ FirstResult = ResultPtr;
}
}
Value *Offset = ConstantInt::get(IntPtrTy, AccumulativeByteOffset);
ResultPtr =
Builder.CreateGEP(Builder.getInt8Ty(), ResultPtr, Offset, "uglygep");
- }
+ } else
+ isSwapCandidate = false;
+
+ // If we created a GEP with constant index, and the base is loop invariant,
+ // then we swap the first one with it, so LICM can move constant GEP out
+ // later.
+ GetElementPtrInst *FirstGEP = dyn_cast<GetElementPtrInst>(FirstResult);
+ GetElementPtrInst *SecondGEP = dyn_cast<GetElementPtrInst>(ResultPtr);
+ if (isSwapCandidate && isLegalToSwapOperand(FirstGEP, SecondGEP, L))
+ swapGEPOperand(FirstGEP, SecondGEP);
+
if (ResultPtr->getType() != Variadic->getType())
ResultPtr = Builder.CreateBitCast(ResultPtr, Variadic->getType());
// Clear the inbounds attribute because the new index may be off-bound.
// e.g.,
//
- // b = add i64 a, 5
- // addr = gep inbounds float, float* p, i64 b
+ // b = add i64 a, 5
+ // addr = gep inbounds float, float* p, i64 b
//
// is transformed to:
//
- // addr2 = gep float, float* p, i64 a ; inbounds removed
- // addr = gep inbounds float, float* addr2, i64 5
+ // addr2 = gep float, float* p, i64 a ; inbounds removed
+ // addr = gep inbounds float, float* addr2, i64 5
//
// If a is -4, although the old index b is in bounds, the new index a is
// off-bound. http://llvm.org/docs/LangRef.html#id181 says "if the
return false;
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
-
+ SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
+ LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
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; ) {
- if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I++)) {
+ for (BasicBlock::iterator I = B->begin(), IE = B->end(); I != IE;)
+ if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I++))
Changed |= splitGEP(GEP);
- }
- // No need to split GEP ConstantExprs because all its indices are constant
- // already.
- }
+ // No need to split GEP ConstantExprs because all its indices are constant
+ // already.
}
+ Changed |= reuniteExts(F);
+
if (VerifyNoDeadCode)
verifyNoDeadCode(F);
return Changed;
}
+Instruction *SeparateConstOffsetFromGEP::findClosestMatchingDominator(
+ const SCEV *Key, Instruction *Dominatee) {
+ auto Pos = DominatingExprs.find(Key);
+ if (Pos == DominatingExprs.end())
+ return nullptr;
+
+ auto &Candidates = Pos->second;
+ // Because we process the basic blocks in pre-order of the dominator tree, a
+ // candidate that doesn't dominate the current instruction won't dominate any
+ // future instruction either. Therefore, we pop it out of the stack. This
+ // optimization makes the algorithm O(n).
+ while (!Candidates.empty()) {
+ Instruction *Candidate = Candidates.back();
+ if (DT->dominates(Candidate, Dominatee))
+ return Candidate;
+ Candidates.pop_back();
+ }
+ return nullptr;
+}
+
+bool SeparateConstOffsetFromGEP::reuniteExts(Instruction *I) {
+ if (!SE->isSCEVable(I->getType()))
+ return false;
+
+ // Dom: LHS+RHS
+ // I: sext(LHS)+sext(RHS)
+ // If Dom can't sign overflow and Dom dominates I, optimize I to sext(Dom).
+ // TODO: handle zext
+ Value *LHS = nullptr, *RHS = nullptr;
+ if (match(I, m_Add(m_SExt(m_Value(LHS)), m_SExt(m_Value(RHS)))) ||
+ match(I, m_Sub(m_SExt(m_Value(LHS)), m_SExt(m_Value(RHS))))) {
+ if (LHS->getType() == RHS->getType()) {
+ const SCEV *Key =
+ SE->getAddExpr(SE->getUnknown(LHS), SE->getUnknown(RHS));
+ if (auto *Dom = findClosestMatchingDominator(Key, I)) {
+ Instruction *NewSExt = new SExtInst(Dom, I->getType(), "", I);
+ NewSExt->takeName(I);
+ I->replaceAllUsesWith(NewSExt);
+ RecursivelyDeleteTriviallyDeadInstructions(I);
+ return true;
+ }
+ }
+ }
+
+ // Add I to DominatingExprs if it's an add/sub that can't sign overflow.
+ if (match(I, m_NSWAdd(m_Value(LHS), m_Value(RHS))) ||
+ match(I, m_NSWSub(m_Value(LHS), m_Value(RHS)))) {
+ if (isKnownNotFullPoison(I)) {
+ const SCEV *Key =
+ SE->getAddExpr(SE->getUnknown(LHS), SE->getUnknown(RHS));
+ DominatingExprs[Key].push_back(I);
+ }
+ }
+ return false;
+}
+
+bool SeparateConstOffsetFromGEP::reuniteExts(Function &F) {
+ bool Changed = false;
+ DominatingExprs.clear();
+ for (auto Node = GraphTraits<DominatorTree *>::nodes_begin(DT);
+ Node != GraphTraits<DominatorTree *>::nodes_end(DT); ++Node) {
+ BasicBlock *BB = Node->getBlock();
+ for (auto I = BB->begin(); I != BB->end(); ) {
+ Instruction *Cur = &*I++;
+ Changed |= reuniteExts(Cur);
+ }
+ }
+ return Changed;
+}
+
void SeparateConstOffsetFromGEP::verifyNoDeadCode(Function &F) {
for (auto &B : F) {
for (auto &I : B) {
}
}
}
+
+bool SeparateConstOffsetFromGEP::isLegalToSwapOperand(
+ GetElementPtrInst *FirstGEP, GetElementPtrInst *SecondGEP, Loop *CurLoop) {
+ if (!FirstGEP || !FirstGEP->hasOneUse())
+ return false;
+
+ if (!SecondGEP || FirstGEP->getParent() != SecondGEP->getParent())
+ return false;
+
+ if (FirstGEP == SecondGEP)
+ return false;
+
+ unsigned FirstNum = FirstGEP->getNumOperands();
+ unsigned SecondNum = SecondGEP->getNumOperands();
+ // Give up if the number of operands are not 2.
+ if (FirstNum != SecondNum || FirstNum != 2)
+ return false;
+
+ Value *FirstBase = FirstGEP->getOperand(0);
+ Value *SecondBase = SecondGEP->getOperand(0);
+ Value *FirstOffset = FirstGEP->getOperand(1);
+ // Give up if the index of the first GEP is loop invariant.
+ if (CurLoop->isLoopInvariant(FirstOffset))
+ return false;
+
+ // Give up if base doesn't have same type.
+ if (FirstBase->getType() != SecondBase->getType())
+ return false;
+
+ Instruction *FirstOffsetDef = dyn_cast<Instruction>(FirstOffset);
+
+ // Check if the second operand of first GEP has constant coefficient.
+ // For an example, for the following code, we won't gain anything by
+ // hoisting the second GEP out because the second GEP can be folded away.
+ // %scevgep.sum.ur159 = add i64 %idxprom48.ur, 256
+ // %67 = shl i64 %scevgep.sum.ur159, 2
+ // %uglygep160 = getelementptr i8* %65, i64 %67
+ // %uglygep161 = getelementptr i8* %uglygep160, i64 -1024
+
+ // Skip constant shift instruction which may be generated by Splitting GEPs.
+ if (FirstOffsetDef && FirstOffsetDef->isShift() &&
+ isa<ConstantInt>(FirstOffsetDef->getOperand(1)))
+ FirstOffsetDef = dyn_cast<Instruction>(FirstOffsetDef->getOperand(0));
+
+ // Give up if FirstOffsetDef is an Add or Sub with constant.
+ // Because it may not profitable at all due to constant folding.
+ if (FirstOffsetDef)
+ if (BinaryOperator *BO = dyn_cast<BinaryOperator>(FirstOffsetDef)) {
+ unsigned opc = BO->getOpcode();
+ if ((opc == Instruction::Add || opc == Instruction::Sub) &&
+ (isa<ConstantInt>(BO->getOperand(0)) ||
+ isa<ConstantInt>(BO->getOperand(1))))
+ return false;
+ }
+ return true;
+}
+
+bool SeparateConstOffsetFromGEP::hasMoreThanOneUseInLoop(Value *V, Loop *L) {
+ int UsesInLoop = 0;
+ for (User *U : V->users()) {
+ if (Instruction *User = dyn_cast<Instruction>(U))
+ if (L->contains(User))
+ if (++UsesInLoop > 1)
+ return true;
+ }
+ return false;
+}
+
+void SeparateConstOffsetFromGEP::swapGEPOperand(GetElementPtrInst *First,
+ GetElementPtrInst *Second) {
+ Value *Offset1 = First->getOperand(1);
+ Value *Offset2 = Second->getOperand(1);
+ First->setOperand(1, Offset2);
+ Second->setOperand(1, Offset1);
+
+ // We changed p+o+c to p+c+o, p+c may not be inbound anymore.
+ const DataLayout &DAL = First->getModule()->getDataLayout();
+ APInt Offset(DAL.getPointerSizeInBits(
+ cast<PointerType>(First->getType())->getAddressSpace()),
+ 0);
+ Value *NewBase =
+ First->stripAndAccumulateInBoundsConstantOffsets(DAL, Offset);
+ uint64_t ObjectSize;
+ if (!getObjectSize(NewBase, ObjectSize, DAL, TLI) ||
+ Offset.ugt(ObjectSize)) {
+ First->setIsInBounds(false);
+ Second->setIsInBounds(false);
+ } else
+ First->setIsInBounds(true);
+}
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