//===- InstCombineLoadStoreAlloca.cpp -------------------------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file implements the visit functions for load, store and alloca. // //===----------------------------------------------------------------------===// #include "InstCombineInternal.h" #include "llvm/ADT/MapVector.h" #include "llvm/ADT/SetOperations.h" #include "llvm/ADT/SmallString.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/Loads.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/DebugInfoMetadata.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/PatternMatch.h" #include "llvm/Transforms/InstCombine/InstCombiner.h" #include "llvm/Transforms/Utils/Local.h" usingnamespacellvm; usingnamespacePatternMatch; #define DEBUG_TYPE … STATISTIC(NumDeadStore, "Number of dead stores eliminated"); STATISTIC(NumGlobalCopies, "Number of allocas copied from constant global"); static cl::opt<unsigned> MaxCopiedFromConstantUsers( "instcombine-max-copied-from-constant-users", cl::init(300), cl::desc("Maximum users to visit in copy from constant transform"), cl::Hidden); namespace llvm { cl::opt<bool> EnableInferAlignmentPass( "enable-infer-alignment-pass", cl::init(true), cl::Hidden, cl::ZeroOrMore, cl::desc("Enable the InferAlignment pass, disabling alignment inference in " "InstCombine")); } /// isOnlyCopiedFromConstantMemory - Recursively walk the uses of a (derived) /// pointer to an alloca. Ignore any reads of the pointer, return false if we /// see any stores or other unknown uses. If we see pointer arithmetic, keep /// track of whether it moves the pointer (with IsOffset) but otherwise traverse /// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to /// the alloca, and if the source pointer is a pointer to a constant memory /// location, we can optimize this. static bool isOnlyCopiedFromConstantMemory(AAResults *AA, AllocaInst *V, MemTransferInst *&TheCopy, SmallVectorImpl<Instruction *> &ToDelete) { … } /// isOnlyCopiedFromConstantMemory - Return true if the specified alloca is only /// modified by a copy from a constant memory location. If we can prove this, we /// can replace any uses of the alloca with uses of the memory location /// directly. static MemTransferInst * isOnlyCopiedFromConstantMemory(AAResults *AA, AllocaInst *AI, SmallVectorImpl<Instruction *> &ToDelete) { … } /// Returns true if V is dereferenceable for size of alloca. static bool isDereferenceableForAllocaSize(const Value *V, const AllocaInst *AI, const DataLayout &DL) { … } static Instruction *simplifyAllocaArraySize(InstCombinerImpl &IC, AllocaInst &AI, DominatorTree &DT) { … } namespace { // If I and V are pointers in different address space, it is not allowed to // use replaceAllUsesWith since I and V have different types. A // non-target-specific transformation should not use addrspacecast on V since // the two address space may be disjoint depending on target. // // This class chases down uses of the old pointer until reaching the load // instructions, then replaces the old pointer in the load instructions with // the new pointer. If during the chasing it sees bitcast or GEP, it will // create new bitcast or GEP with the new pointer and use them in the load // instruction. class PointerReplacer { … }; } // end anonymous namespace bool PointerReplacer::collectUsers() { … } bool PointerReplacer::collectUsersRecursive(Instruction &I) { … } Value *PointerReplacer::getReplacement(Value *V) { … } void PointerReplacer::replace(Instruction *I) { … } void PointerReplacer::replacePointer(Value *V) { … } Instruction *InstCombinerImpl::visitAllocaInst(AllocaInst &AI) { … } // Are we allowed to form a atomic load or store of this type? static bool isSupportedAtomicType(Type *Ty) { … } /// Helper to combine a load to a new type. /// /// This just does the work of combining a load to a new type. It handles /// metadata, etc., and returns the new instruction. The \c NewTy should be the /// loaded *value* type. This will convert it to a pointer, cast the operand to /// that pointer type, load it, etc. /// /// Note that this will create all of the instructions with whatever insert /// point the \c InstCombinerImpl currently is using. LoadInst *InstCombinerImpl::combineLoadToNewType(LoadInst &LI, Type *NewTy, const Twine &Suffix) { … } /// Combine a store to a new type. /// /// Returns the newly created store instruction. static StoreInst *combineStoreToNewValue(InstCombinerImpl &IC, StoreInst &SI, Value *V) { … } /// Combine loads to match the type of their uses' value after looking /// through intervening bitcasts. /// /// The core idea here is that if the result of a load is used in an operation, /// we should load the type most conducive to that operation. For example, when /// loading an integer and converting that immediately to a pointer, we should /// instead directly load a pointer. /// /// However, this routine must never change the width of a load or the number of /// loads as that would introduce a semantic change. This combine is expected to /// be a semantic no-op which just allows loads to more closely model the types /// of their consuming operations. /// /// Currently, we also refuse to change the precise type used for an atomic load /// or a volatile load. This is debatable, and might be reasonable to change /// later. However, it is risky in case some backend or other part of LLVM is /// relying on the exact type loaded to select appropriate atomic operations. static Instruction *combineLoadToOperationType(InstCombinerImpl &IC, LoadInst &Load) { … } static Instruction *unpackLoadToAggregate(InstCombinerImpl &IC, LoadInst &LI) { … } // If we can determine that all possible objects pointed to by the provided // pointer value are, not only dereferenceable, but also definitively less than // or equal to the provided maximum size, then return true. Otherwise, return // false (constant global values and allocas fall into this category). // // FIXME: This should probably live in ValueTracking (or similar). static bool isObjectSizeLessThanOrEq(Value *V, uint64_t MaxSize, const DataLayout &DL) { … } // If we're indexing into an object of a known size, and the outer index is // not a constant, but having any value but zero would lead to undefined // behavior, replace it with zero. // // For example, if we have: // @f.a = private unnamed_addr constant [1 x i32] [i32 12], align 4 // ... // %arrayidx = getelementptr inbounds [1 x i32]* @f.a, i64 0, i64 %x // ... = load i32* %arrayidx, align 4 // Then we know that we can replace %x in the GEP with i64 0. // // FIXME: We could fold any GEP index to zero that would cause UB if it were // not zero. Currently, we only handle the first such index. Also, we could // also search through non-zero constant indices if we kept track of the // offsets those indices implied. static bool canReplaceGEPIdxWithZero(InstCombinerImpl &IC, GetElementPtrInst *GEPI, Instruction *MemI, unsigned &Idx) { … } // If we're indexing into an object with a variable index for the memory // access, but the object has only one element, we can assume that the index // will always be zero. If we replace the GEP, return it. static Instruction *replaceGEPIdxWithZero(InstCombinerImpl &IC, Value *Ptr, Instruction &MemI) { … } static bool canSimplifyNullStoreOrGEP(StoreInst &SI) { … } static bool canSimplifyNullLoadOrGEP(LoadInst &LI, Value *Op) { … } Instruction *InstCombinerImpl::visitLoadInst(LoadInst &LI) { … } /// Look for extractelement/insertvalue sequence that acts like a bitcast. /// /// \returns underlying value that was "cast", or nullptr otherwise. /// /// For example, if we have: /// /// %E0 = extractelement <2 x double> %U, i32 0 /// %V0 = insertvalue [2 x double] undef, double %E0, 0 /// %E1 = extractelement <2 x double> %U, i32 1 /// %V1 = insertvalue [2 x double] %V0, double %E1, 1 /// /// and the layout of a <2 x double> is isomorphic to a [2 x double], /// then %V1 can be safely approximated by a conceptual "bitcast" of %U. /// Note that %U may contain non-undef values where %V1 has undef. static Value *likeBitCastFromVector(InstCombinerImpl &IC, Value *V) { … } /// Combine stores to match the type of value being stored. /// /// The core idea here is that the memory does not have any intrinsic type and /// where we can we should match the type of a store to the type of value being /// stored. /// /// However, this routine must never change the width of a store or the number of /// stores as that would introduce a semantic change. This combine is expected to /// be a semantic no-op which just allows stores to more closely model the types /// of their incoming values. /// /// Currently, we also refuse to change the precise type used for an atomic or /// volatile store. This is debatable, and might be reasonable to change later. /// However, it is risky in case some backend or other part of LLVM is relying /// on the exact type stored to select appropriate atomic operations. /// /// \returns true if the store was successfully combined away. This indicates /// the caller must erase the store instruction. We have to let the caller erase /// the store instruction as otherwise there is no way to signal whether it was /// combined or not: IC.EraseInstFromFunction returns a null pointer. static bool combineStoreToValueType(InstCombinerImpl &IC, StoreInst &SI) { … } static bool unpackStoreToAggregate(InstCombinerImpl &IC, StoreInst &SI) { … } /// equivalentAddressValues - Test if A and B will obviously have the same /// value. This includes recognizing that %t0 and %t1 will have the same /// value in code like this: /// %t0 = getelementptr \@a, 0, 3 /// store i32 0, i32* %t0 /// %t1 = getelementptr \@a, 0, 3 /// %t2 = load i32* %t1 /// static bool equivalentAddressValues(Value *A, Value *B) { … } Instruction *InstCombinerImpl::visitStoreInst(StoreInst &SI) { … } /// Try to transform: /// if () { *P = v1; } else { *P = v2 } /// or: /// *P = v1; if () { *P = v2; } /// into a phi node with a store in the successor. bool InstCombinerImpl::mergeStoreIntoSuccessor(StoreInst &SI) { … }
Codebase Browser
llvm