X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FSeparateConstOffsetFromGEP.cpp;h=86a10d2a16122866da0ff6043c5c382cd04cad53;hb=0890b95b60c353074d8d3a2e11906e66282e30da;hp=b8529e174cad12529849230c5c72ee6ddb8c09e2;hpb=585644611e1f696bbd8f95a5eb75fc808b1cfdb6;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp b/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp index b8529e174ca..86a10d2a161 100644 --- a/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp +++ b/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp @@ -79,26 +79,119 @@ // 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 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 + VerifyNoDeadCode("reassociate-geps-verify-no-dead-code", cl::init(false), + cl::desc("Verify this pass produces no dead code"), + cl::Hidden); namespace { @@ -116,98 +209,215 @@ 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: - /// Extracts a constant offset from the given GEP index. It outputs the - /// numeric value of the extracted constant offset (0 if failed), and a +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). + /// the constant offset), or nullptr if we cannot extract a constant offset. /// \p Idx The given GEP index - /// \p NewIdx The new index to replace - /// \p DL The datalayout of the module - /// \p IP Calculating the new index requires new instructions. IP indicates - /// where to insert them (typically right before the GEP). - static int64_t Extract(Value *Idx, Value *&NewIdx, const DataLayout *DL, - Instruction *IP); - /// Looks for a constant offset without extracting it. The meaning of the - /// arguments and the return value are the same as Extract. - static int64_t Find(Value *Idx, const DataLayout *DL); - - private: - ConstantOffsetExtractor(const DataLayout *Layout, Instruction *InsertionPt) - : DL(Layout), IP(InsertionPt) {} - /// Searches the expression that computes V for a constant offset. If the - /// searching is successful, update UserChain as a path from V to the constant - /// offset. - int64_t find(Value *V); - /// A helper function to look into both operands of a binary operator U. - /// \p IsSub Whether U is a sub operator. If so, we need to negate the - /// constant offset at some point. - int64_t findInEitherOperand(User *U, bool IsSub); - /// After finding the constant offset and how it is reached from the GEP - /// index, we build a new index which is a clone of the old one except the - /// constant offset is removed. For example, given (a + (b + 5)) and knowning - /// the constant offset is 5, this function returns (a + b). + /// \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)) /// - /// We cannot simply change the constant to zero because the expression that - /// computes the index or its intermediate result may be used by others. - Value *rebuildWithoutConstantOffset(); - // A helper function for rebuildWithoutConstantOffset that rebuilds the direct - // user (U) of the constant offset (C). - Value *rebuildLeafWithoutConstantOffset(User *U, Value *C); - /// Returns a clone of U except the first occurrence of From with To. - Value *cloneAndReplace(User *U, Value *From, Value *To); - - /// 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; - /// Finds the first use of Used in U. Returns -1 if not found. - static unsigned FindFirstUse(User *U, Value *Used); - /// Returns whether OPC (sext or zext) can be distributed to the operands of - /// BO. e.g., sext can be distributed to the operands of an "add nsw" because - /// sext (add nsw a, b) == add nsw (sext a), (sext b). - static bool Distributable(unsigned OPC, BinaryOperator *BO); + /// \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 rebuildWithoutConstantOffset rebuild the new GEP index. + /// This path helps to rebuild the new GEP index. SmallVector UserChain; - /// The data layout of the module. Used in ComputeKnownBits. - const DataLayout *DL; + /// A data structure used in rebuildWithoutConstOffset. Contains all + /// sext/zext instructions along UserChain. + SmallVector 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: +public: static char ID; - SeparateConstOffsetFromGEP() : FunctionPass(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(); - AU.addRequired(); + AU.addRequired(); + AU.addRequired(); + AU.addRequired(); + AU.addRequired(); + AU.setPreservesCFG(); + AU.addRequired(); + } + + bool doInitialization(Module &M) override { + 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); - /// Finds the constant offset within each index, and accumulates them. This - /// function only inspects the GEP without changing it. The output - /// NeedsExtraction indicates whether we can extract a non-zero constant - /// offset from any index. - int64_t accumulateByteOffset(GetElementPtrInst *GEP, const DataLayout *DL, - bool &NeedsExtraction); + /// 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 that is equivalent to . + 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> DominatingExprs; }; } // anonymous namespace @@ -216,213 +426,315 @@ 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_AG_DEPENDENCY(TargetTransformInfo) -INITIALIZE_PASS_DEPENDENCY(DataLayoutPass) +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() { - return new SeparateConstOffsetFromGEP(); +FunctionPass * +llvm::createSeparateConstOffsetFromGEPPass(const TargetMachine *TM, + bool LowerGEP) { + return new SeparateConstOffsetFromGEP(TM, LowerGEP); } -bool ConstantOffsetExtractor::Distributable(unsigned OPC, BinaryOperator *BO) { - assert(OPC == Instruction::SExt || OPC == Instruction::ZExt); +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(LHS)) { + if (!ConstLHS->isNegative()) + return true; + } + if (ConstantInt *ConstRHS = dyn_cast(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) { - return (OPC == Instruction::SExt && BO->hasNoSignedWrap()) || - (OPC == Instruction::ZExt && BO->hasNoUnsignedWrap()); + if (SignExtended && !BO->hasNoSignedWrap()) + return false; + if (ZeroExtended && !BO->hasNoUnsignedWrap()) + return false; } - // sext/zext (and/or/xor A, B) == and/or/xor (sext/zext A), (sext/zext B) - // -instcombine also leverages this invariant to do the reverse - // transformation to reduce integer casts. - return BO->getOpcode() == Instruction::And || - BO->getOpcode() == Instruction::Or || - BO->getOpcode() == Instruction::Xor; + return true; } -int64_t ConstantOffsetExtractor::findInEitherOperand(User *U, bool IsSub) { - assert(U->getNumOperands() == 2); - int64_t ConstantOffset = find(U->getOperand(0)); +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(U->getOperand(1)); + ConstantOffset = find(BO->getOperand(1), SignExtended, ZeroExtended, + /* NonNegative */ false); // If U is a sub operator, negate the constant offset found in the right // operand. - return IsSub ? -ConstantOffset : ConstantOffset; + if (BO->getOpcode() == Instruction::Sub) + ConstantOffset = -ConstantOffset; + return ConstantOffset; } -int64_t ConstantOffsetExtractor::find(Value *V) { - // TODO(jingyue): We can even trace into integer/pointer casts, such as +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. - assert(V->getType()->isIntegerTy()); + unsigned BitWidth = cast(V->getType())->getBitWidth(); + // We cannot do much with Values that are not a User, such as an Argument. User *U = dyn_cast(V); - // We cannot do much with Values that are not a User, such as BasicBlock and - // MDNode. - if (U == nullptr) return 0; + if (U == nullptr) return APInt(BitWidth, 0); - int64_t ConstantOffset = 0; - if (ConstantInt *CI = dyn_cast(U)) { + APInt ConstantOffset(BitWidth, 0); + if (ConstantInt *CI = dyn_cast(V)) { // Hooray, we found it! - ConstantOffset = CI->getSExtValue(); - } else if (Operator *O = dyn_cast(U)) { - // The GEP index may be more complicated than a simple addition of a - // varaible and a constant. Therefore, we trace into subexpressions for more - // hoisting opportunities. - switch (O->getOpcode()) { - case Instruction::Add: { - ConstantOffset = findInEitherOperand(U, false); - break; - } - case Instruction::Sub: { - ConstantOffset = findInEitherOperand(U, true); - break; - } - case Instruction::Or: { - // If LHS and RHS don't have common bits, (LHS | RHS) is equivalent to - // (LHS + RHS). - if (NoCommonBits(U->getOperand(0), U->getOperand(1))) - ConstantOffset = findInEitherOperand(U, false); - break; - } - case Instruction::SExt: - case Instruction::ZExt: { - // We trace into sext/zext if the operator can be distributed to its - // operand. e.g., we can transform into "sext (add nsw a, 5)" and - // extract constant 5, because - // sext (add nsw a, 5) == add nsw (sext a), 5 - if (BinaryOperator *BO = dyn_cast(U->getOperand(0))) { - if (Distributable(O->getOpcode(), BO)) - ConstantOffset = find(U->getOperand(0)); - } - break; - } - } + ConstantOffset = CI->getValue(); + } else if (BinaryOperator *BO = dyn_cast(V)) { + // Trace into subexpressions for more hoisting opportunities. + if (CanTraceInto(SignExtended, ZeroExtended, BO, NonNegative)) + ConstantOffset = findInEitherOperand(BO, SignExtended, ZeroExtended); + } else if (isa(V)) { + ConstantOffset = find(U->getOperand(0), /* SignExtended */ true, + ZeroExtended, NonNegative).sext(BitWidth); + } else if (isa(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, adds it to the path for future - // transformation (rebuildWithoutConstantOffset). Zero is a valid constant - // offset, but doesn't help this optimization. + + // 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; } -unsigned ConstantOffsetExtractor::FindFirstUse(User *U, Value *Used) { - for (unsigned I = 0, E = U->getNumOperands(); I < E; ++I) { - if (U->getOperand(I) == Used) - return I; +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(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 -1; + return Current; } -Value *ConstantOffsetExtractor::cloneAndReplace(User *U, Value *From, - Value *To) { - // Finds in U the first use of From. It is safe to ignore future occurrences - // of From, because findInEitherOperand similarly stops searching the right - // operand when the first operand has a non-zero constant offset. - unsigned OpNo = FindFirstUse(U, From); - assert(OpNo != (unsigned)-1 && "UserChain wasn't built correctly"); - - // ConstantOffsetExtractor::find only follows Operators (i.e., Instructions - // and ConstantExprs). Therefore, U is either an Instruction or a - // ConstantExpr. - if (Instruction *I = dyn_cast(U)) { - Instruction *Clone = I->clone(); - Clone->setOperand(OpNo, To); - Clone->insertBefore(IP); - return Clone; - } - // cast(To) is safe because a ConstantExpr only uses Constants. - return cast(U) - ->getWithOperandReplaced(OpNo, cast(To)); +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::rebuildLeafWithoutConstantOffset(User *U, - Value *C) { - assert(U->getNumOperands() <= 2 && - "We didn't trace into any operator with more than 2 operands"); - // If U has only one operand which is the constant offset, removing the - // constant offset leaves U as a null value. - if (U->getNumOperands() == 1) - return Constant::getNullValue(U->getType()); - - // U->getNumOperands() == 2 - unsigned OpNo = FindFirstUse(U, C); // U->getOperand(OpNo) == C - assert(OpNo < 2 && "UserChain wasn't built correctly"); - Value *TheOther = U->getOperand(1 - OpNo); // The other operand of U - // If U = C - X, removing C makes U = -X; otherwise U will simply be X. - if (!isa(U) || OpNo == 1) - return TheOther; - if (isa(U)) - return ConstantExpr::getNeg(cast(TheOther)); - return BinaryOperator::CreateNeg(TheOther, "", IP); -} +Value * +ConstantOffsetExtractor::distributeExtsAndCloneChain(unsigned ChainIndex) { + User *U = UserChain[ChainIndex]; + if (ChainIndex == 0) { + assert(isa(U)); + // If U is a ConstantInt, applyExts will return a ConstantInt as well. + return UserChain[ChainIndex] = cast(applyExts(U)); + } -Value *ConstantOffsetExtractor::rebuildWithoutConstantOffset() { - assert(UserChain.size() > 0 && "you at least found a constant, right?"); - // Start with the constant and go up through UserChain, each time building a - // clone of the subexpression but with the constant removed. - // e.g., to build a clone of (a + (b + (c + 5)) but with the 5 removed, we - // first c, then (b + c), and finally (a + (b + c)). - // - // Fast path: if the GEP index is a constant, simply returns 0. - if (UserChain.size() == 1) - return ConstantInt::get(UserChain[0]->getType(), 0); - - Value *Remainder = - rebuildLeafWithoutConstantOffset(UserChain[1], UserChain[0]); - for (size_t I = 2; I < UserChain.size(); ++I) - Remainder = cloneAndReplace(UserChain[I], UserChain[I - 1], Remainder); - return Remainder; + if (CastInst *Cast = dyn_cast(U)) { + assert((isa(Cast) || isa(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(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; } -int64_t ConstantOffsetExtractor::Extract(Value *Idx, Value *&NewIdx, - const DataLayout *DL, - Instruction *IP) { - ConstantOffsetExtractor Extractor(DL, IP); - // Find a non-zero constant offset first. - int64_t ConstantOffset = Extractor.find(Idx); - if (ConstantOffset == 0) - return 0; - // Then rebuild a new index with the constant removed. - NewIdx = Extractor.rebuildWithoutConstantOffset(); - return ConstantOffset; +Value *ConstantOffsetExtractor::removeConstOffset(unsigned ChainIndex) { + if (ChainIndex == 0) { + assert(isa(UserChain[ChainIndex])); + return ConstantInt::getNullValue(UserChain[ChainIndex]->getType()); + } + + BinaryOperator *BO = cast(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(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; } -int64_t ConstantOffsetExtractor::Find(Value *Idx, const DataLayout *DL) { - return ConstantOffsetExtractor(DL, nullptr).find(Idx); +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; } -void ConstantOffsetExtractor::ComputeKnownBits(Value *V, APInt &KnownOne, - APInt &KnownZero) const { - IntegerType *IT = cast(V->getType()); - KnownOne = APInt(IT->getBitWidth(), 0); - KnownZero = APInt(IT->getBitWidth(), 0); - llvm::computeKnownBits(V, KnownZero, KnownOne, DL, 0); +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 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; + 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(*GTI)) { + if ((*I)->getType() != IntPtrTy) { + *I = CastInst::CreateIntegerCast(*I, IntPtrTy, true, "idxprom", GEP); + Changed = true; + } + } + } + return Changed; } -int64_t SeparateConstOffsetFromGEP::accumulateByteOffset( - GetElementPtrInst *GEP, const DataLayout *DL, bool &NeedsExtraction) { +int64_t +SeparateConstOffsetFromGEP::accumulateByteOffset(GetElementPtrInst *GEP, + bool &NeedsExtraction) { NeedsExtraction = false; int64_t AccumulativeByteOffset = 0; gep_type_iterator GTI = gep_type_begin(*GEP); @@ -430,7 +742,7 @@ int64_t SeparateConstOffsetFromGEP::accumulateByteOffset( if (isa(*GTI)) { // Tries to extract a constant offset from this GEP index. int64_t ConstantOffset = - ConstantOffsetExtractor::Find(GEP->getOperand(I), DL); + ConstantOffsetExtractor::Find(GEP->getOperand(I), GEP, DT); if (ConstantOffset != 0) { NeedsExtraction = true; // A GEP may have multiple indices. We accumulate the extracted @@ -439,11 +751,137 @@ int64_t SeparateConstOffsetFromGEP::accumulateByteOffset( AccumulativeByteOffset += ConstantOffset * DL->getTypeAllocSize(GTI.getIndexedType()); } + } else if (LowerGEP) { + StructType *StTy = cast(*GTI); + uint64_t Field = cast(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(*GTI)) { + Value *Idx = Variadic->getOperand(I); + // Skip zero indices. + if (ConstantInt *CI = dyn_cast(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(FirstResult); + GetElementPtrInst *SecondGEP = dyn_cast(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(*GTI)) { + Value *Idx = Variadic->getOperand(I); + // Skip zero indices. + if (ConstantInt *CI = dyn_cast(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()) @@ -454,83 +892,97 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) { if (GEP->hasAllConstantIndices()) return false; - bool Changed = false; - - // Shortcuts integer casts. Eliminating these explicit casts can make - // subsequent optimizations more obvious: ConstantOffsetExtractor needn't - // trace into these casts. - if (GEP->isInBounds()) { - // Doing this to inbounds GEPs is safe because their indices are guaranteed - // to be non-negative and in bounds. - gep_type_iterator GTI = gep_type_begin(*GEP); - for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I, ++GTI) { - if (isa(*GTI)) { - if (Operator *O = dyn_cast(GEP->getOperand(I))) { - if (O->getOpcode() == Instruction::SExt || - O->getOpcode() == Instruction::ZExt) { - GEP->setOperand(I, O->getOperand(0)); - Changed = true; - } - } - } - } - } + bool Changed = canonicalizeArrayIndicesToPointerSize(GEP); - const DataLayout *DL = &getAnalysis().getDataLayout(); bool NeedsExtraction; - int64_t AccumulativeByteOffset = - accumulateByteOffset(GEP, DL, NeedsExtraction); + int64_t AccumulativeByteOffset = accumulateByteOffset(GEP, NeedsExtraction); if (!NeedsExtraction) return Changed; - // 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. - TargetTransformInfo &TTI = getAnalysis(); - if (!TTI.isLegalAddressingMode(GEP->getType()->getElementType(), - /*BaseGV=*/nullptr, AccumulativeByteOffset, - /*HasBaseReg=*/true, /*Scale=*/0)) { - 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().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 GEP index. The resultant GEP computes - // the variadic base. + // 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(*GTI)) { - Value *NewIdx = nullptr; - // Tries to extract a constant offset from this GEP index. - int64_t ConstantOffset = - ConstantOffsetExtractor::Extract(GEP->getOperand(I), NewIdx, DL, GEP); - if (ConstantOffset != 0) { - assert(NewIdx != nullptr && - "ConstantOffset != 0 implies NewIdx is set"); + // 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); - // Clear the inbounds attribute because the new index may be off-bound. - // e.g., - // - // b = add i64 a, 5 - // addr = gep inbounds float* p, i64 b - // - // is transformed to: - // - // addr2 = gep float* p, i64 a - // addr = gep 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. - GEP->setIsInBounds(false); - Changed = true; + // 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 @@ -562,18 +1014,21 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *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( + DL->getTypeAllocSize(GEP->getType()->getElementType())); Type *IntPtrTy = DL->getIntPtrType(GEP->getType()); - uint64_t ElementTypeSizeOfGEP = - DL->getTypeAllocSize(GEP->getType()->getElementType()); 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). - // Per ANSI C standard, signed / unsigned = unsigned. Therefore, we - // cast ElementTypeSizeOfGEP to signed. - int64_t Index = - AccumulativeByteOffset / static_cast(ElementTypeSizeOfGEP); - NewGEP = GetElementPtrInst::Create( - NewGEP, ConstantInt::get(IntPtrTy, Index, true), GEP->getName(), 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(NewGEP)->setIsInBounds(GEPWasInBounds); } else { // Unlikely but possible. For example, // #pragma pack(1) @@ -593,8 +1048,11 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) { 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); + // Inherit the inbounds attribute of the original GEP. + cast(NewGEP)->setIsInBounds(GEPWasInBounds); if (GEP->getType() != I8PtrTy) NewGEP = new BitCastInst(NewGEP, GEP->getType(), GEP->getName(), GEP); } @@ -606,18 +1064,202 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) { } bool SeparateConstOffsetFromGEP::runOnFunction(Function &F) { + if (skipOptnoneFunction(F)) + return false; + if (DisableSeparateConstOffsetFromGEP) return false; + DT = &getAnalysis().getDomTree(); + SE = &getAnalysis().getSE(); + LI = &getAnalysis().getLoopInfo(); + TLI = &getAnalysis().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(I++)) { + for (BasicBlock::iterator I = B->begin(), IE = B->end(); I != IE;) + if (GetElementPtrInst *GEP = dyn_cast(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; } - // No need to split GEP ConstantExprs because all its indices are constant - // already. + } + } + + // 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::nodes_begin(DT); + Node != GraphTraits::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(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(FirstOffsetDef->getOperand(1))) + FirstOffsetDef = dyn_cast(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(FirstOffsetDef)) { + unsigned opc = BO->getOpcode(); + if ((opc == Instruction::Add || opc == Instruction::Sub) && + (isa(BO->getOperand(0)) || + isa(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(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(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); +}