//===-- SeparateConstOffsetFromGEP.cpp - ------------------------*- C++ -*-===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // Loop unrolling may create many similar GEPs for array accesses. // e.g., a 2-level loop // // float a[32][32]; // global variable // // for (int i = 0; i < 2; ++i) { // for (int j = 0; j < 2; ++j) { // ... // ... = a[x + i][y + j]; // ... // } // } // // will probably be unrolled to: // // gep %a, 0, %x, %y; load // gep %a, 0, %x, %y + 1; load // gep %a, 0, %x + 1, %y; load // gep %a, 0, %x + 1, %y + 1; load // // LLVM's GVN does not use partial redundancy elimination yet, and is thus // unable to reuse (gep %a, 0, %x, %y). As a result, this misoptimization incurs // significant slowdown in targets with limited addressing modes. For instance, // because the PTX target does not support the reg+reg addressing mode, the // NVPTX backend emits PTX code that literally computes the pointer address of // each GEP, wasting tons of registers. It emits the following PTX for the // first load and similar PTX for other loads. // // mov.u32 %r1, %x; // mov.u32 %r2, %y; // mul.wide.u32 %rl2, %r1, 128; // mov.u64 %rl3, a; // add.s64 %rl4, %rl3, %rl2; // mul.wide.u32 %rl5, %r2, 4; // add.s64 %rl6, %rl4, %rl5; // ld.global.f32 %f1, [%rl6]; // // To reduce the register pressure, the optimization implemented in this file // merges the common part of a group of GEPs, so we can compute each pointer // address by adding a simple offset to the common part, saving many registers. // // It works by splitting each GEP into a variadic base and a constant offset. // The variadic base can be computed once and reused by multiple GEPs, and the // constant offsets can be nicely folded into the reg+immediate addressing mode // (supported by most targets) without using any extra register. // // For instance, we transform the four GEPs and four loads in the above example // into: // // base = gep a, 0, x, y // load base // laod base + 1 * sizeof(float) // load base + 32 * sizeof(float) // load base + 33 * sizeof(float) // // Given the transformed IR, a backend that supports the reg+immediate // addressing mode can easily fold the pointer arithmetics into the loads. For // example, the NVPTX backend can easily fold the pointer arithmetics into the // ld.global.f32 instructions, and the resultant PTX uses much fewer registers. // // mov.u32 %r1, %tid.x; // mov.u32 %r2, %tid.y; // mul.wide.u32 %rl2, %r1, 128; // mov.u64 %rl3, a; // add.s64 %rl4, %rl3, %rl2; // mul.wide.u32 %rl5, %r2, 4; // add.s64 %rl6, %rl4, %rl5; // ld.global.f32 %f1, [%rl6]; // so far the same as unoptimized PTX // ld.global.f32 %f2, [%rl6+4]; // much better // ld.global.f32 %f3, [%rl6+128]; // much better // ld.global.f32 %f4, [%rl6+132]; // much better // // Another improvement enabled by the LowerGEP flag is to lower a GEP with // multiple indices to either multiple GEPs with a single index or arithmetic // operations (depending on whether the target uses alias analysis in codegen). // Such transformation can have following benefits: // (1) It can always extract constants in the indices of structure type. // (2) After such Lowering, there are more optimization opportunities such as // CSE, LICM and CGP. // // E.g. The following GEPs have multiple indices: // BB1: // %p = getelementptr [10 x %struct]* %ptr, i64 %i, i64 %j1, i32 3 // load %p // ... // BB2: // %p2 = getelementptr [10 x %struct]* %ptr, i64 %i, i64 %j1, i32 2 // load %p2 // ... // // We can not do CSE for to the common part related to index "i64 %i". Lowering // GEPs can achieve such goals. // If the target does not use alias analysis in codegen, this pass will // lower a GEP with multiple indices into arithmetic operations: // BB1: // %1 = ptrtoint [10 x %struct]* %ptr to i64 ; CSE opportunity // %2 = mul i64 %i, length_of_10xstruct ; CSE opportunity // %3 = add i64 %1, %2 ; CSE opportunity // %4 = mul i64 %j1, length_of_struct // %5 = add i64 %3, %4 // %6 = add i64 %3, struct_field_3 ; Constant offset // %p = inttoptr i64 %6 to i32* // load %p // ... // BB2: // %7 = ptrtoint [10 x %struct]* %ptr to i64 ; CSE opportunity // %8 = mul i64 %i, length_of_10xstruct ; CSE opportunity // %9 = add i64 %7, %8 ; CSE opportunity // %10 = mul i64 %j2, length_of_struct // %11 = add i64 %9, %10 // %12 = add i64 %11, struct_field_2 ; Constant offset // %p = inttoptr i64 %12 to i32* // load %p2 // ... // // If the target uses alias analysis in codegen, this pass will lower a GEP // with multiple indices into multiple GEPs with a single index: // BB1: // %1 = bitcast [10 x %struct]* %ptr to i8* ; CSE opportunity // %2 = mul i64 %i, length_of_10xstruct ; CSE opportunity // %3 = getelementptr i8* %1, i64 %2 ; CSE opportunity // %4 = mul i64 %j1, length_of_struct // %5 = getelementptr i8* %3, i64 %4 // %6 = getelementptr i8* %5, struct_field_3 ; Constant offset // %p = bitcast i8* %6 to i32* // load %p // ... // BB2: // %7 = bitcast [10 x %struct]* %ptr to i8* ; CSE opportunity // %8 = mul i64 %i, length_of_10xstruct ; CSE opportunity // %9 = getelementptr i8* %7, i64 %8 ; CSE opportunity // %10 = mul i64 %j2, length_of_struct // %11 = getelementptr i8* %9, i64 %10 // %12 = getelementptr i8* %11, struct_field_2 ; Constant offset // %p2 = bitcast i8* %12 to i32* // load %p2 // ... // // Lowering GEPs can also benefit other passes such as LICM and CGP. // LICM (Loop Invariant Code Motion) can not hoist/sink a GEP of multiple // indices if one of the index is variant. If we lower such GEP into invariant // parts and variant parts, LICM can hoist/sink those invariant parts. // CGP (CodeGen Prepare) tries to sink address calculations that match the // target's addressing modes. A GEP with multiple indices may not match and will // not be sunk. If we lower such GEP into smaller parts, CGP may sink some of // them. So we end up with a better addressing mode. // //===----------------------------------------------------------------------===// #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/DataLayout.h" #include "llvm/IR/Dominators.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/Transforms/Scalar.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/Target/TargetMachine.h" #include "llvm/Target/TargetSubtargetInfo.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), 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 { /// \brief A helper class for separating a constant offset from a GEP index. /// /// In real programs, a GEP index may be more complicated than a simple addition /// of something and a constant integer which can be trivially splitted. For /// example, to split ((a << 3) | 5) + b, we need to search deeper for the /// constant offset, so that we can separate the index to (a << 3) + b and 5. /// /// Therefore, this class looks into the expression that computes a given GEP /// index, and tries to find a constant integer that can be hoisted to the /// outermost level of the expression as an addition. Not every constant in an /// expression can jump out. e.g., we cannot transform (b * (a + 5)) to (b * a + /// 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: /// 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 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, GetElementPtrInst *GEP, const DominatorTree *DT); 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; /// otherwise, UserChain is empty. /// /// \p V The given expression /// \p SignExtended Whether V will be sign-extended in the computation of the /// GEP index /// \p ZeroExtended Whether V will be zero-extended in the computation of the /// GEP index /// \p NonNegative Whether V is guaranteed to be non-negative. For example, /// an index of an inbounds GEP is guaranteed to be /// non-negative. Levaraging this, we can better split /// inbounds GEPs. APInt find(Value *V, bool SignExtended, bool ZeroExtended, bool NonNegative); /// A helper function to look into both operands of a binary operator. APInt findInEitherOperand(BinaryOperator *BO, bool SignExtended, bool ZeroExtended); /// After finding the constant offset C from the GEP index I, we build a new /// index I' s.t. I' + C = I. This function builds and returns the new /// index I' according to UserChain produced by function "find". /// /// The building conceptually takes two steps: /// 1) iteratively distribute s/zext towards the leaves of the expression tree /// that computes I /// 2) reassociate the expression tree to the form I' + C. /// /// For example, to extract the 5 from sext(a + (b + 5)), we first distribute /// sext to a, b and 5 so that we have /// sext(a) + (sext(b) + 5). /// Then, we reassociate it to /// (sext(a) + sext(b)) + 5. /// Given this form, we know I' is sext(a) + sext(b). Value *rebuildWithoutConstOffset(); /// After the first step of rebuilding the GEP index without the constant /// offset, distribute s/zext to the operands of all operators in UserChain. /// e.g., zext(sext(a + (b + 5)) (assuming no overflow) => /// zext(sext(a)) + (zext(sext(b)) + zext(sext(5))). /// /// The function also updates UserChain to point to new subexpressions after /// distributing s/zext. e.g., the old UserChain of the above example is /// 5 -> b + 5 -> a + (b + 5) -> sext(...) -> zext(sext(...)), /// and the new UserChain is /// zext(sext(5)) -> zext(sext(b)) + zext(sext(5)) -> /// zext(sext(a)) + (zext(sext(b)) + zext(sext(5)) /// /// \p ChainIndex The index to UserChain. ChainIndex is initially /// UserChain.size() - 1, and is decremented during /// the recursion. Value *distributeExtsAndCloneChain(unsigned ChainIndex); /// Reassociates the GEP index to the form I' + C and returns I'. Value *removeConstOffset(unsigned ChainIndex); /// A helper function to apply ExtInsts, a list of s/zext, to value V. /// e.g., if ExtInsts = [sext i32 to i64, zext i16 to i32], this function /// returns "sext i32 (zext i16 V to i32) to i64". Value *applyExts(Value *V); /// A helper function that returns whether we can trace into the operands /// of binary operator BO for a constant offset. /// /// \p SignExtended Whether BO is surrounded by sext /// \p ZeroExtended Whether BO is surrounded by zext /// \p NonNegative Whether BO is known to be non-negative, e.g., an in-bound /// array index. bool CanTraceInto(bool SignExtended, bool ZeroExtended, BinaryOperator *BO, bool NonNegative); /// The path from the constant offset to the old GEP index. e.g., if the GEP /// index is "a * b + (c + 5)". After running function find, UserChain[0] will /// be the constant 5, UserChain[1] will be the subexpression "c + 5", and /// UserChain[2] will be the entire expression "a * b + (c + 5)". /// /// This path helps to rebuild the new GEP index. SmallVector<User *, 8> UserChain; /// A data structure used in rebuildWithoutConstOffset. Contains all /// sext/zext instructions along UserChain. SmallVector<CastInst *, 16> ExtInsts; 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: static char ID; SeparateConstOffsetFromGEP(const TargetMachine *TM = nullptr, bool LowerGEP = false) : FunctionPass(ID), DL(nullptr), DT(nullptr), TM(TM), LowerGEP(LowerGEP) { initializeSeparateConstOffsetFromGEPPass(*PassRegistry::getPassRegistry()); } 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 { DL = &M.getDataLayout(); return false; } bool runOnFunction(Function &F) override; 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); /// Lower a GEP with multiple indices into multiple GEPs with a single index. /// Function splitGEP already split the original GEP into a variadic part and /// a constant offset (i.e., AccumulativeByteOffset). This function lowers the /// variadic part into a set of GEPs with a single index and applies /// AccumulativeByteOffset to it. /// \p Variadic The variadic part of the original GEP. /// \p AccumulativeByteOffset The constant offset. void lowerToSingleIndexGEPs(GetElementPtrInst *Variadic, int64_t AccumulativeByteOffset); /// Lower a GEP with multiple indices into ptrtoint+arithmetics+inttoptr form. /// Function splitGEP already split the original GEP into a variadic part and /// a constant offset (i.e., AccumulativeByteOffset). This function lowers the /// variadic part into a set of arithmetic operations and applies /// AccumulativeByteOffset to it. /// \p Variadic The variadic part of the original GEP. /// \p AccumulativeByteOffset The constant offset. void lowerToArithmetics(GetElementPtrInst *Variadic, int64_t AccumulativeByteOffset); /// Finds the constant offset within each index and accumulates them. If /// LowerGEP is true, it finds in indices of both sequential and structure /// types, otherwise it only finds in sequential indices. The output /// NeedsExtraction indicates whether we successfully find a non-zero constant /// offset. int64_t accumulateByteOffset(GetElementPtrInst *GEP, bool &NeedsExtraction); /// Canonicalize array indices to pointer-size integers. This helps to /// simplify the logic of splitting a GEP. For example, if a + b is a /// pointer-size integer, we have /// gep base, a + b = gep (gep base, a), b /// However, this equality may not hold if the size of a + b is smaller than /// the pointer size, because LLVM conceptually sign-extends GEP indices to /// pointer size before computing the address /// (http://llvm.org/docs/LangRef.html#id181). /// /// This canonicalization is very likely already done in clang and /// instcombine. Therefore, the program will probably remain the same. /// /// Returns true if the module changes. /// /// 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; 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 char SeparateConstOffsetFromGEP::ID = 0; INITIALIZE_PASS_BEGIN( 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(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, false) FunctionPass * llvm::createSeparateConstOffsetFromGEPPass(const TargetMachine *TM, bool LowerGEP) { return new SeparateConstOffsetFromGEP(TM, LowerGEP); } bool ConstantOffsetExtractor::CanTraceInto(bool SignExtended, bool ZeroExtended, BinaryOperator *BO, bool NonNegative) { // We only consider ADD, SUB and OR, because a non-zero constant found in // expressions composed of these operations can be easily hoisted as a // constant offset by reassociation. if (BO->getOpcode() != Instruction::Add && BO->getOpcode() != Instruction::Sub && BO->getOpcode() != Instruction::Or) { return 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 && !haveNoCommonBitsSet(LHS, RHS, DL, nullptr, BO, DT)) return false; // In addition, tracing into BO requires that its surrounding s/zext (if // any) is distributable to both operands. // // Suppose BO = A op B. // SignExtended | ZeroExtended | Distributable? // --------------+--------------+---------------------------------- // 0 | 0 | true because no s/zext exists // 0 | 1 | zext(BO) == zext(A) op zext(B) // 1 | 0 | sext(BO) == sext(A) op sext(B) // 1 | 1 | zext(sext(BO)) == // | | zext(sext(A)) op zext(sext(B)) if (BO->getOpcode() == Instruction::Add && !ZeroExtended && NonNegative) { // If a + b >= 0 and (a >= 0 or b >= 0), then // sext(a + b) = sext(a) + sext(b) // even if the addition is not marked nsw. // // Leveraging this invarient, we can trace into an sext'ed inbound GEP // index if the constant offset is non-negative. // // Verified in @sext_add in split-gep.ll. if (ConstantInt *ConstLHS = dyn_cast<ConstantInt>(LHS)) { if (!ConstLHS->isNegative()) return true; } if (ConstantInt *ConstRHS = dyn_cast<ConstantInt>(RHS)) { if (!ConstRHS->isNegative()) return true; } } // sext (add/sub nsw A, B) == add/sub nsw (sext A), (sext B) // zext (add/sub nuw A, B) == add/sub nuw (zext A), (zext B) if (BO->getOpcode() == Instruction::Add || BO->getOpcode() == Instruction::Sub) { if (SignExtended && !BO->hasNoSignedWrap()) return false; if (ZeroExtended && !BO->hasNoUnsignedWrap()) return false; } return true; } APInt ConstantOffsetExtractor::findInEitherOperand(BinaryOperator *BO, bool SignExtended, bool ZeroExtended) { // BO being non-negative does not shed light on whether its operands are // non-negative. Clear the NonNegative flag here. APInt ConstantOffset = find(BO->getOperand(0), SignExtended, ZeroExtended, /* NonNegative */ false); // If we found a constant offset in the left operand, stop and return that. // This shortcut might cause us to miss opportunities of combining the // constant offsets in both operands, e.g., (a + 4) + (b + 5) => (a + b) + 9. // However, such cases are probably already handled by -instcombine, // given this pass runs after the standard optimizations. if (ConstantOffset != 0) return ConstantOffset; ConstantOffset = find(BO->getOperand(1), SignExtended, ZeroExtended, /* NonNegative */ false); // If U is a sub operator, negate the constant offset found in the right // operand. if (BO->getOpcode() == Instruction::Sub) ConstantOffset = -ConstantOffset; return ConstantOffset; } APInt ConstantOffsetExtractor::find(Value *V, bool SignExtended, bool ZeroExtended, bool NonNegative) { // TODO(jingyue): We could trace into integer/pointer casts, such as // inttoptr, ptrtoint, bitcast, and addrspacecast. We choose to handle only // integers because it gives good enough results for our benchmarks. unsigned BitWidth = cast<IntegerType>(V->getType())->getBitWidth(); // We cannot do much with Values that are not a User, such as an Argument. User *U = dyn_cast<User>(V); if (U == nullptr) return APInt(BitWidth, 0); APInt ConstantOffset(BitWidth, 0); if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) { // Hooray, we found it! ConstantOffset = CI->getValue(); } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V)) { // Trace into subexpressions for more hoisting opportunities. 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); } else if (isa<ZExtInst>(V)) { // As an optimization, we can clear the SignExtended flag because // sext(zext(a)) = zext(a). Verified in @sext_zext in split-gep.ll. // // Clear the NonNegative flag, because zext(a) >= 0 does not imply a >= 0. ConstantOffset = find(U->getOperand(0), /* SignExtended */ false, /* ZeroExtended */ true, /* NonNegative */ false).zext(BitWidth); } // If we found a non-zero constant offset, add it to the path for // rebuildWithoutConstOffset. Zero is a valid constant offset, but doesn't // help this optimization. if (ConstantOffset != 0) UserChain.push_back(U); return ConstantOffset; } Value *ConstantOffsetExtractor::applyExts(Value *V) { Value *Current = V; // ExtInsts is built in the use-def order. Therefore, we apply them to V // in the reversed order. for (auto I = ExtInsts.rbegin(), E = ExtInsts.rend(); I != E; ++I) { if (Constant *C = dyn_cast<Constant>(Current)) { // If Current is a constant, apply s/zext using ConstantExpr::getCast. // ConstantExpr::getCast emits a ConstantInt if C is a ConstantInt. Current = ConstantExpr::getCast((*I)->getOpcode(), C, (*I)->getType()); } else { Instruction *Ext = (*I)->clone(); Ext->setOperand(0, Current); Ext->insertBefore(IP); Current = Ext; } } return Current; } Value *ConstantOffsetExtractor::rebuildWithoutConstOffset() { distributeExtsAndCloneChain(UserChain.size() - 1); // Remove all nullptrs (used to be s/zext) from UserChain. unsigned NewSize = 0; for (auto I = UserChain.begin(), E = UserChain.end(); I != E; ++I) { if (*I != nullptr) { UserChain[NewSize] = *I; NewSize++; } } UserChain.resize(NewSize); return removeConstOffset(UserChain.size() - 1); } Value * ConstantOffsetExtractor::distributeExtsAndCloneChain(unsigned ChainIndex) { User *U = UserChain[ChainIndex]; if (ChainIndex == 0) { assert(isa<ConstantInt>(U)); // If U is a ConstantInt, applyExts will return a ConstantInt as well. return UserChain[ChainIndex] = cast<ConstantInt>(applyExts(U)); } if (CastInst *Cast = dyn_cast<CastInst>(U)) { assert((isa<SExtInst>(Cast) || isa<ZExtInst>(Cast)) && "We only traced into two types of CastInst: sext and zext"); ExtInsts.push_back(Cast); UserChain[ChainIndex] = nullptr; return distributeExtsAndCloneChain(ChainIndex - 1); } // Function find only trace into BinaryOperator and CastInst. BinaryOperator *BO = cast<BinaryOperator>(U); // OpNo = which operand of BO is UserChain[ChainIndex - 1] unsigned OpNo = (BO->getOperand(0) == UserChain[ChainIndex - 1] ? 0 : 1); Value *TheOther = applyExts(BO->getOperand(1 - OpNo)); Value *NextInChain = distributeExtsAndCloneChain(ChainIndex - 1); BinaryOperator *NewBO = nullptr; if (OpNo == 0) { NewBO = BinaryOperator::Create(BO->getOpcode(), NextInChain, TheOther, BO->getName(), IP); } else { NewBO = BinaryOperator::Create(BO->getOpcode(), TheOther, NextInChain, BO->getName(), IP); } return UserChain[ChainIndex] = NewBO; } Value *ConstantOffsetExtractor::removeConstOffset(unsigned ChainIndex) { if (ChainIndex == 0) { assert(isa<ConstantInt>(UserChain[ChainIndex])); return ConstantInt::getNullValue(UserChain[ChainIndex]->getType()); } 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); Value *TheOther = BO->getOperand(1 - OpNo); // If NextInChain is 0 and not the LHS of a sub, we can simplify the // sub-expression to be just TheOther. if (ConstantInt *CI = dyn_cast<ConstantInt>(NextInChain)) { if (CI->isZero() && !(BO->getOpcode() == Instruction::Sub && OpNo == 0)) 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. // // For instance, given // a | (b + 5) where a and b + 5 have no common bits, // we can extract 5 as the constant offset. // // However, reusing the "or" in the new index would give us // (a | b) + 5 // which does not equal a | (b + 5). // // Replacing the "or" with "add" is fine, because // a | (b + 5) = a + (b + 5) = (a + b) + 5 NewOp = Instruction::Add; } 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, 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) { UserChainTail = nullptr; return nullptr; } // Separates the constant offset from the GEP index. Value *IdxWithoutConstOffset = Extractor.rebuildWithoutConstOffset(); UserChainTail = Extractor.UserChain.back(); return IdxWithoutConstOffset; } 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(GEP, DT) .find(Idx, /* SignExtended */ false, /* ZeroExtended */ false, GEP->isInBounds()) .getSExtValue(); } bool SeparateConstOffsetFromGEP::canonicalizeArrayIndicesToPointerSize( GetElementPtrInst *GEP) { bool Changed = false; Type *IntPtrTy = DL->getIntPtrType(GEP->getType()); gep_type_iterator GTI = gep_type_begin(*GEP); for (User::op_iterator I = GEP->op_begin() + 1, E = GEP->op_end(); I != E; ++I, ++GTI) { // Skip struct member indices which must be i32. if (isa<SequentialType>(*GTI)) { if ((*I)->getType() != IntPtrTy) { *I = CastInst::CreateIntegerCast(*I, IntPtrTy, true, "idxprom", GEP); Changed = true; } } } return Changed; } int64_t SeparateConstOffsetFromGEP::accumulateByteOffset(GetElementPtrInst *GEP, bool &NeedsExtraction) { NeedsExtraction = false; int64_t AccumulativeByteOffset = 0; gep_type_iterator GTI = gep_type_begin(*GEP); for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) { if (isa<SequentialType>(*GTI)) { // Tries to extract a constant offset from this GEP index. int64_t ConstantOffset = ConstantOffsetExtractor::Find(GEP->getOperand(I), GEP, DT); if (ConstantOffset != 0) { NeedsExtraction = true; // A GEP may have multiple indices. We accumulate the extracted // constant offset to a byte offset, and later offset the remainder of // the original GEP with this byte offset. AccumulativeByteOffset += ConstantOffset * DL->getTypeAllocSize(GTI.getIndexedType()); } } else if (LowerGEP) { StructType *StTy = cast<StructType>(*GTI); uint64_t Field = cast<ConstantInt>(GEP->getOperand(I))->getZExtValue(); // Skip field 0 as the offset is always 0. if (Field != 0) { NeedsExtraction = true; AccumulativeByteOffset += DL->getStructLayout(StTy)->getElementOffset(Field); } } } return AccumulativeByteOffset; } void SeparateConstOffsetFromGEP::lowerToSingleIndexGEPs( GetElementPtrInst *Variadic, int64_t AccumulativeByteOffset) { IRBuilder<> Builder(Variadic); Type *IntPtrTy = DL->getIntPtrType(Variadic->getType()); 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); gep_type_iterator GTI = gep_type_begin(*Variadic); // Create an ugly GEP for each sequential index. We don't create GEPs for // structure indices, as they are accumulated in the constant offset index. for (unsigned I = 1, E = Variadic->getNumOperands(); I != E; ++I, ++GTI) { if (isa<SequentialType>(*GTI)) { Value *Idx = Variadic->getOperand(I); // Skip zero indices. if (ConstantInt *CI = dyn_cast<ConstantInt>(Idx)) if (CI->isZero()) continue; APInt ElementSize = APInt(IntPtrTy->getIntegerBitWidth(), DL->getTypeAllocSize(GTI.getIndexedType())); // Scale the index by element size. if (ElementSize != 1) { if (ElementSize.isPowerOf2()) { Idx = Builder.CreateShl( Idx, ConstantInt::get(IntPtrTy, ElementSize.logBase2())); } else { Idx = Builder.CreateMul(Idx, ConstantInt::get(IntPtrTy, ElementSize)); } } // Create an ugly GEP with a single index for each index. ResultPtr = Builder.CreateGEP(Builder.getInt8Ty(), ResultPtr, Idx, "uglygep"); if (FirstResult == nullptr) FirstResult = ResultPtr; } } // Create a GEP with the constant offset index. if (AccumulativeByteOffset != 0) { 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()); Variadic->replaceAllUsesWith(ResultPtr); Variadic->eraseFromParent(); } void SeparateConstOffsetFromGEP::lowerToArithmetics(GetElementPtrInst *Variadic, int64_t AccumulativeByteOffset) { IRBuilder<> Builder(Variadic); Type *IntPtrTy = DL->getIntPtrType(Variadic->getType()); Value *ResultPtr = Builder.CreatePtrToInt(Variadic->getOperand(0), IntPtrTy); gep_type_iterator GTI = gep_type_begin(*Variadic); // Create ADD/SHL/MUL arithmetic operations for each sequential indices. We // don't create arithmetics for structure indices, as they are accumulated // in the constant offset index. for (unsigned I = 1, E = Variadic->getNumOperands(); I != E; ++I, ++GTI) { if (isa<SequentialType>(*GTI)) { Value *Idx = Variadic->getOperand(I); // Skip zero indices. if (ConstantInt *CI = dyn_cast<ConstantInt>(Idx)) if (CI->isZero()) continue; APInt ElementSize = APInt(IntPtrTy->getIntegerBitWidth(), DL->getTypeAllocSize(GTI.getIndexedType())); // Scale the index by element size. if (ElementSize != 1) { if (ElementSize.isPowerOf2()) { Idx = Builder.CreateShl( Idx, ConstantInt::get(IntPtrTy, ElementSize.logBase2())); } else { Idx = Builder.CreateMul(Idx, ConstantInt::get(IntPtrTy, ElementSize)); } } // Create an ADD for each index. ResultPtr = Builder.CreateAdd(ResultPtr, Idx); } } // Create an ADD for the constant offset index. if (AccumulativeByteOffset != 0) { ResultPtr = Builder.CreateAdd( ResultPtr, ConstantInt::get(IntPtrTy, AccumulativeByteOffset)); } ResultPtr = Builder.CreateIntToPtr(ResultPtr, Variadic->getType()); Variadic->replaceAllUsesWith(ResultPtr); Variadic->eraseFromParent(); } bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) { // Skip vector GEPs. if (GEP->getType()->isVectorTy()) return false; // The backend can already nicely handle the case where all indices are // constant. if (GEP->hasAllConstantIndices()) return false; bool Changed = canonicalizeArrayIndicesToPointerSize(GEP); bool NeedsExtraction; int64_t AccumulativeByteOffset = accumulateByteOffset(GEP, NeedsExtraction); if (!NeedsExtraction) return Changed; // If LowerGEP is disabled, before really splitting the GEP, check whether the // backend supports the addressing mode we are about to produce. If no, this // splitting probably won't be beneficial. // If LowerGEP is enabled, even the extracted constant offset can not match // the addressing mode, we can still do optimizations to other lowered parts // of variable indices. Therefore, we don't check for addressing modes in that // case. if (!LowerGEP) { 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, AddrSpace)) { return Changed; } } // Remove the constant offset in each sequential index. The resultant GEP // computes the variadic base. // Notice that we don't remove struct field indices here. If LowerGEP is // disabled, a structure index is not accumulated and we still use the old // one. If LowerGEP is enabled, a structure index is accumulated in the // constant offset. LowerToSingleIndexGEPs or lowerToArithmetics will later // handle the constant offset and won't need a new structure index. gep_type_iterator GTI = gep_type_begin(*GEP); for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) { 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(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); } } } // 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 // // is transformed to: // // 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 // inbounds keyword is not present, the offsets are added to the base // address with silently-wrapping two's complement arithmetic". // Therefore, the final code will be a semantically equivalent. // // TODO(jingyue): do some range analysis to keep as many inbounds as // possible. GEPs with inbounds are more friendly to alias analysis. bool GEPWasInBounds = GEP->isInBounds(); GEP->setIsInBounds(false); // Lowers a GEP to either GEPs with a single index or arithmetic operations. if (LowerGEP) { // As currently BasicAA does not analyze ptrtoint/inttoptr, do not lower to // arithmetic operations if the target uses alias analysis in codegen. if (TM && TM->getSubtargetImpl(*GEP->getParent()->getParent())->useAA()) lowerToSingleIndexGEPs(GEP, AccumulativeByteOffset); else lowerToArithmetics(GEP, AccumulativeByteOffset); return true; } // No need to create another GEP if the accumulative byte offset is 0. if (AccumulativeByteOffset == 0) return true; // Offsets the base with the accumulative byte offset. // // %gep ; the base // ... %gep ... // // => add the offset // // %gep2 ; clone of %gep // %new.gep = gep %gep2, <offset / sizeof(*%gep)> // %gep ; will be removed // ... %gep ... // // => replace all uses of %gep with %new.gep and remove %gep // // %gep2 ; clone of %gep // %new.gep = gep %gep2, <offset / sizeof(*%gep)> // ... %new.gep ... // // If AccumulativeByteOffset is not a multiple of sizeof(*%gep), we emit an // uglygep (http://llvm.org/docs/GetElementPtr.html#what-s-an-uglygep): // bitcast %gep2 to i8*, add the offset, and bitcast the result back to the // type of %gep. // // %gep2 ; clone of %gep // %0 = bitcast %gep2 to i8* // %uglygep = gep %0, <offset> // %new.gep = bitcast %uglygep to <type of %gep> // ... %new.gep ... Instruction *NewGEP = GEP->clone(); NewGEP->insertBefore(GEP); // Per ANSI C standard, signed / unsigned = unsigned and signed % unsigned = // unsigned.. Therefore, we cast ElementTypeSizeOfGEP to signed because it is // used with unsigned integers later. int64_t ElementTypeSizeOfGEP = static_cast<int64_t>( DL->getTypeAllocSize(GEP->getType()->getElementType())); Type *IntPtrTy = DL->getIntPtrType(GEP->getType()); if (AccumulativeByteOffset % ElementTypeSizeOfGEP == 0) { // 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(GEP->getResultElementType(), NewGEP, ConstantInt::get(IntPtrTy, Index, true), GEP->getName(), GEP); // Inherit the inbounds attribute of the original GEP. cast<GetElementPtrInst>(NewGEP)->setIsInBounds(GEPWasInBounds); } else { // Unlikely but possible. For example, // #pragma pack(1) // struct S { // int a[3]; // int64 b[8]; // }; // #pragma pack() // // Suppose the gep before extraction is &s[i + 1].b[j + 3]. After // extraction, it becomes &s[i].b[j] and AccumulativeByteOffset is // sizeof(S) + 3 * sizeof(int64) = 100, which is not a multiple of // sizeof(int64). // // Emit an uglygep in this case. Type *I8PtrTy = Type::getInt8PtrTy(GEP->getContext(), GEP->getPointerAddressSpace()); NewGEP = new BitCastInst(NewGEP, I8PtrTy, "", GEP); NewGEP = GetElementPtrInst::Create( Type::getInt8Ty(GEP->getContext()), NewGEP, ConstantInt::get(IntPtrTy, AccumulativeByteOffset, true), "uglygep", GEP); // Inherit the inbounds attribute of the original GEP. cast<GetElementPtrInst>(NewGEP)->setIsInBounds(GEPWasInBounds); if (GEP->getType() != I8PtrTy) NewGEP = new BitCastInst(NewGEP, GEP->getType(), GEP->getName(), GEP); } GEP->replaceAllUsesWith(NewGEP); GEP->eraseFromParent(); return true; } bool SeparateConstOffsetFromGEP::runOnFunction(Function &F) { if (skipOptnoneFunction(F)) return false; if (DisableSeparateConstOffsetFromGEP) 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++)) Changed |= splitGEP(GEP); // 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) { if (isInstructionTriviallyDead(&I)) { std::string ErrMessage; raw_string_ostream RSO(ErrMessage); RSO << "Dead instruction detected!\n" << I << "\n"; llvm_unreachable(RSO.str().c_str()); } } } } 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() && dyn_cast<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) && (dyn_cast<ConstantInt>(BO->getOperand(0)) || dyn_cast<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); }