1894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman//===- Loads.cpp - Local load analysis ------------------------------------===// 2894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman// 3894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman// The LLVM Compiler Infrastructure 4894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman// 5894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman// This file is distributed under the University of Illinois Open Source 6894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman// License. See LICENSE.TXT for details. 7894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman// 8894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman//===----------------------------------------------------------------------===// 9894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman// 10894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman// This file defines simple local analyses for load instructions. 11894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman// 12894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman//===----------------------------------------------------------------------===// 13894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 14894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman#include "llvm/Analysis/Loads.h" 15894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman#include "llvm/Analysis/AliasAnalysis.h" 16894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman#include "llvm/Target/TargetData.h" 17894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman#include "llvm/GlobalAlias.h" 18894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman#include "llvm/GlobalVariable.h" 19894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman#include "llvm/IntrinsicInst.h" 2019bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman#include "llvm/Operator.h" 21894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Baumanusing namespace llvm; 22894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 23894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// AreEquivalentAddressValues - Test if A and B will obviously have the same 24894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// value. This includes recognizing that %t0 and %t1 will have the same 25894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// value in code like this: 26894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// %t0 = getelementptr \@a, 0, 3 27894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// store i32 0, i32* %t0 28894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// %t1 = getelementptr \@a, 0, 3 29894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// %t2 = load i32* %t1 30894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// 31894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Baumanstatic bool AreEquivalentAddressValues(const Value *A, const Value *B) { 32894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Test if the values are trivially equivalent. 33894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (A == B) return true; 3419bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman 35894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Test if the values come from identical arithmetic instructions. 36894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Use isIdenticalToWhenDefined instead of isIdenticalTo because 37894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // this function is only used when one address use dominates the 38894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // other, which means that they'll always either have the same 39894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // value or one of them will have an undefined value. 40894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (isa<BinaryOperator>(A) || isa<CastInst>(A) || 41894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman isa<PHINode>(A) || isa<GetElementPtrInst>(A)) 42894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (const Instruction *BI = dyn_cast<Instruction>(B)) 43894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI)) 44894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return true; 4519bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman 46894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Otherwise they may not be equivalent. 47894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return false; 48894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman} 49894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 50894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// getUnderlyingObjectWithOffset - Strip off up to MaxLookup GEPs and 51894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// bitcasts to get back to the underlying object being addressed, keeping 52894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// track of the offset in bytes from the GEPs relative to the result. 5319bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman/// This is closely related to GetUnderlyingObject but is located 54894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// here to avoid making VMCore depend on TargetData. 55894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Baumanstatic Value *getUnderlyingObjectWithOffset(Value *V, const TargetData *TD, 56894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman uint64_t &ByteOffset, 57894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman unsigned MaxLookup = 6) { 58894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (!V->getType()->isPointerTy()) 59894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return V; 60894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) { 61894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) { 62894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (!GEP->hasAllConstantIndices()) 63894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return V; 64894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman SmallVector<Value*, 8> Indices(GEP->op_begin() + 1, GEP->op_end()); 65894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman ByteOffset += TD->getIndexedOffset(GEP->getPointerOperandType(), 6619bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman Indices); 67894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman V = GEP->getPointerOperand(); 68894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } else if (Operator::getOpcode(V) == Instruction::BitCast) { 69894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman V = cast<Operator>(V)->getOperand(0); 70894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { 71894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (GA->mayBeOverridden()) 72894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return V; 73894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman V = GA->getAliasee(); 74894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } else { 75894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return V; 76894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 77894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman assert(V->getType()->isPointerTy() && "Unexpected operand type!"); 78894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 79894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return V; 80894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman} 81894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 82894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// isSafeToLoadUnconditionally - Return true if we know that executing a load 83894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// from this value cannot trap. If it is not obviously safe to load from the 84894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// specified pointer, we do a quick local scan of the basic block containing 85894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// ScanFrom, to determine if the address is already accessed. 86894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Baumanbool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom, 87894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman unsigned Align, const TargetData *TD) { 88894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman uint64_t ByteOffset = 0; 89894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman Value *Base = V; 90894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (TD) 91894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman Base = getUnderlyingObjectWithOffset(V, TD, ByteOffset); 92894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 9319bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman Type *BaseType = 0; 94894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman unsigned BaseAlign = 0; 95894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (const AllocaInst *AI = dyn_cast<AllocaInst>(Base)) { 96894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // An alloca is safe to load from as load as it is suitably aligned. 97894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman BaseType = AI->getAllocatedType(); 98894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman BaseAlign = AI->getAlignment(); 99894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } else if (const GlobalValue *GV = dyn_cast<GlobalValue>(Base)) { 100894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Global variables are safe to load from but their size cannot be 101894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // guaranteed if they are overridden. 102894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (!isa<GlobalAlias>(GV) && !GV->mayBeOverridden()) { 103894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman BaseType = GV->getType()->getElementType(); 104894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman BaseAlign = GV->getAlignment(); 105894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 106894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 107894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 108894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (BaseType && BaseType->isSized()) { 109894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (TD && BaseAlign == 0) 110894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman BaseAlign = TD->getPrefTypeAlignment(BaseType); 111894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 112894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (Align <= BaseAlign) { 113894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (!TD) 114894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return true; // Loading directly from an alloca or global is OK. 115894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 116894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Check if the load is within the bounds of the underlying object. 11719bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman PointerType *AddrTy = cast<PointerType>(V->getType()); 118894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman uint64_t LoadSize = TD->getTypeStoreSize(AddrTy->getElementType()); 119894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (ByteOffset + LoadSize <= TD->getTypeAllocSize(BaseType) && 120894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman (Align == 0 || (ByteOffset % Align) == 0)) 121894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return true; 122894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 123894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 124894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 125894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Otherwise, be a little bit aggressive by scanning the local block where we 126894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // want to check to see if the pointer is already being loaded or stored 127894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // from/to. If so, the previous load or store would have already trapped, 128894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // so there is no harm doing an extra load (also, CSE will later eliminate 129894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // the load entirely). 130894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman BasicBlock::iterator BBI = ScanFrom, E = ScanFrom->getParent()->begin(); 131894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 132894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman while (BBI != E) { 133894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman --BBI; 134894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 135894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // If we see a free or a call which may write to memory (i.e. which might do 136894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // a free) the pointer could be marked invalid. 137894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (isa<CallInst>(BBI) && BBI->mayWriteToMemory() && 13819bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman !isa<DbgInfoIntrinsic>(BBI)) 139894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return false; 140894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 141894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) { 142894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (AreEquivalentAddressValues(LI->getOperand(0), V)) return true; 143894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } else if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) { 144894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (AreEquivalentAddressValues(SI->getOperand(1), V)) return true; 145894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 146894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 147894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return false; 148894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman} 149894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 150894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the 151894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// instruction before ScanFrom) checking to see if we have the value at the 152894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// memory address *Ptr locally available within a small number of instructions. 153894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// If the value is available, return it. 154894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// 155894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// If not, return the iterator for the last validated instruction that the 156894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// value would be live through. If we scanned the entire block and didn't find 157894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// something that invalidates *Ptr or provides it, ScanFrom would be left at 158894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// begin() and this returns null. ScanFrom could also be left 159894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// 160894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// MaxInstsToScan specifies the maximum instructions to scan in the block. If 161894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// it is set to 0, it will scan the whole block. You can also optionally 162894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman/// specify an alias analysis implementation, which makes this more precise. 163894018228b0e0bdbd7aa7e8f47d4a9458789ca82John BaumanValue *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, 164894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman BasicBlock::iterator &ScanFrom, 165894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman unsigned MaxInstsToScan, 166894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman AliasAnalysis *AA) { 167894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (MaxInstsToScan == 0) MaxInstsToScan = ~0U; 168894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 169894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // If we're using alias analysis to disambiguate get the size of *Ptr. 17019bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman uint64_t AccessSize = 0; 171894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (AA) { 17219bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType(); 173894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman AccessSize = AA->getTypeStoreSize(AccessTy); 174894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 175894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 176894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman while (ScanFrom != ScanBB->begin()) { 177894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // We must ignore debug info directives when counting (otherwise they 178894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // would affect codegen). 179894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman Instruction *Inst = --ScanFrom; 18019bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman if (isa<DbgInfoIntrinsic>(Inst)) 181894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman continue; 182894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 183894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Restore ScanFrom to expected value in case next test succeeds 184894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman ScanFrom++; 185894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 186894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Don't scan huge blocks. 187894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (MaxInstsToScan-- == 0) return 0; 188894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 189894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman --ScanFrom; 190894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // If this is a load of Ptr, the loaded value is available. 19119bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman // (This is true even if the load is volatile or atomic, although 19219bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman // those cases are unlikely.) 193894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) 194894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (AreEquivalentAddressValues(LI->getOperand(0), Ptr)) 195894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return LI; 196894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 197894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 198894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // If this is a store through Ptr, the value is available! 19919bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman // (This is true even if the store is volatile or atomic, although 20019bac1e08be200c31efd26f0f5fd144c9b3eefd3John Bauman // those cases are unlikely.) 201894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (AreEquivalentAddressValues(SI->getOperand(1), Ptr)) 202894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return SI->getOperand(0); 203894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 204894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // If Ptr is an alloca and this is a store to a different alloca, ignore 205894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // the store. This is a trivial form of alias analysis that is important 206894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // for reg2mem'd code. 207894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) && 208894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman (isa<AllocaInst>(SI->getOperand(1)) || 209894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman isa<GlobalVariable>(SI->getOperand(1)))) 210894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman continue; 211894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 212894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // If we have alias analysis and it says the store won't modify the loaded 213894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // value, ignore the store. 214894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (AA && 215894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman (AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) 216894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman continue; 217894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 218894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Otherwise the store that may or may not alias the pointer, bail out. 219894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman ++ScanFrom; 220894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return 0; 221894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 222894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 223894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // If this is some other instruction that may clobber Ptr, bail out. 224894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (Inst->mayWriteToMemory()) { 225894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // If alias analysis claims that it really won't modify the load, 226894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // ignore it. 227894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman if (AA && 228894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman (AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) 229894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman continue; 230894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 231894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // May modify the pointer, bail out. 232894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman ++ScanFrom; 233894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return 0; 234894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 235894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman } 236894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman 237894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // Got to the start of the block, we didn't find it, but are done for this 238894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman // block. 239894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman return 0; 240894018228b0e0bdbd7aa7e8f47d4a9458789ca82John Bauman} 241