X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FLoads.cpp;h=5042eb9777ac9fbb9dd1f550c69cdcb619a9d027;hb=9f6a38fc70875e1f6066da05bd2bd38686a73239;hp=005d309894c1cec4b598683e988ef4c299952d2e;hpb=570e52c6f17d8819ee4c8595fc79d17a6dc51dd9;p=oota-llvm.git diff --git a/lib/Analysis/Loads.cpp b/lib/Analysis/Loads.cpp index 005d309894c..5042eb9777a 100644 --- a/lib/Analysis/Loads.cpp +++ b/lib/Analysis/Loads.cpp @@ -22,25 +22,29 @@ #include "llvm/IR/Operator.h" using namespace llvm; -/// AreEquivalentAddressValues - Test if A and B will obviously have the same -/// value. This includes recognizing that %t0 and %t1 will have the same +/// \brief 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: +/// \code /// %t0 = getelementptr \@a, 0, 3 /// store i32 0, i32* %t0 /// %t1 = getelementptr \@a, 0, 3 /// %t2 = load i32* %t1 +/// \endcode /// static bool AreEquivalentAddressValues(const Value *A, const Value *B) { // Test if the values are trivially equivalent. - if (A == B) return true; + if (A == B) + return true; // Test if the values come from identical arithmetic instructions. // Use isIdenticalToWhenDefined instead of isIdenticalTo because // this function is only used when one address use dominates the // other, which means that they'll always either have the same // value or one of them will have an undefined value. - if (isa(A) || isa(A) || - isa(A) || isa(A)) + if (isa(A) || isa(A) || isa(A) || + isa(A)) if (const Instruction *BI = dyn_cast(B)) if (cast(A)->isIdenticalToWhenDefined(BI)) return true; @@ -49,15 +53,19 @@ static bool AreEquivalentAddressValues(const Value *A, const Value *B) { return false; } -/// isSafeToLoadUnconditionally - Return true if we know that executing a load -/// from this value cannot trap. If it is not obviously safe to load from the -/// specified pointer, we do a quick local scan of the basic block containing -/// ScanFrom, to determine if the address is already accessed. +/// \brief Check if executing a load of this pointer value cannot trap. +/// +/// If it is not obviously safe to load from the specified pointer, we do +/// a quick local scan of the basic block containing \c ScanFrom, to determine +/// if the address is already accessed. +/// +/// This uses the pointee type to determine how many bytes need to be safe to +/// load from the pointer. bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom, - unsigned Align, const DataLayout *TD) { + unsigned Align, const DataLayout *DL) { int64_t ByteOffset = 0; Value *Base = V; - Base = GetPointerBaseWithConstantOffset(V, ByteOffset, TD); + Base = GetPointerBaseWithConstantOffset(V, ByteOffset, DL); if (ByteOffset < 0) // out of bounds return false; @@ -69,26 +77,29 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom, BaseType = AI->getAllocatedType(); BaseAlign = AI->getAlignment(); } else if (const GlobalVariable *GV = dyn_cast(Base)) { - // Global variables are safe to load from but their size cannot be - // guaranteed if they are overridden. + // Global variables are not necessarily safe to load from if they are + // overridden. Their size may change or they may be weak and require a test + // to determine if they were in fact provided. if (!GV->mayBeOverridden()) { BaseType = GV->getType()->getElementType(); BaseAlign = GV->getAlignment(); } } - if (BaseType && BaseType->isSized()) { - if (TD && BaseAlign == 0) - BaseAlign = TD->getPrefTypeAlignment(BaseType); + PointerType *AddrTy = cast(V->getType()); + uint64_t LoadSize = DL ? DL->getTypeStoreSize(AddrTy->getElementType()) : 0; - if (Align <= BaseAlign) { - if (!TD) - return true; // Loading directly from an alloca or global is OK. + // If we found a base allocated type from either an alloca or global variable, + // try to see if we are definitively within the allocated region. We need to + // know the size of the base type and the loaded type to do anything in this + // case, so only try this when we have the DataLayout available. + if (BaseType && BaseType->isSized() && DL) { + if (BaseAlign == 0) + BaseAlign = DL->getPrefTypeAlignment(BaseType); + if (Align <= BaseAlign) { // Check if the load is within the bounds of the underlying object. - PointerType *AddrTy = cast(V->getType()); - uint64_t LoadSize = TD->getTypeStoreSize(AddrTy->getElementType()); - if (ByteOffset + LoadSize <= TD->getTypeAllocSize(BaseType) && + if (ByteOffset + LoadSize <= DL->getTypeAllocSize(BaseType) && (Align == 0 || (ByteOffset % Align) == 0)) return true; } @@ -101,6 +112,10 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom, // the load entirely). BasicBlock::iterator BBI = ScanFrom, E = ScanFrom->getParent()->begin(); + // We can at least always strip pointer casts even though we can't use the + // base here. + V = V->stripPointerCasts(); + while (BBI != E) { --BBI; @@ -110,46 +125,67 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom, !isa(BBI)) return false; - if (LoadInst *LI = dyn_cast(BBI)) { - if (AreEquivalentAddressValues(LI->getOperand(0), V)) return true; - } else if (StoreInst *SI = dyn_cast(BBI)) { - if (AreEquivalentAddressValues(SI->getOperand(1), V)) return true; - } + Value *AccessedPtr; + if (LoadInst *LI = dyn_cast(BBI)) + AccessedPtr = LI->getPointerOperand(); + else if (StoreInst *SI = dyn_cast(BBI)) + AccessedPtr = SI->getPointerOperand(); + else + continue; + + // Handle trivial cases even w/o DataLayout or other work. + if (AccessedPtr == V) + return true; + + if (!DL) + continue; + + auto *AccessedTy = cast(AccessedPtr->getType()); + if (AreEquivalentAddressValues(AccessedPtr->stripPointerCasts(), V) && + LoadSize <= DL->getTypeStoreSize(AccessedTy->getElementType())) + return true; } return false; } -/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the -/// instruction before ScanFrom) checking to see if we have the value at the +/// \brief Scan the ScanBB block backwards to see if we have the value at the /// memory address *Ptr locally available within a small number of instructions. -/// If the value is available, return it. /// -/// If not, return the iterator for the last validated instruction that the -/// value would be live through. If we scanned the entire block and didn't find -/// something that invalidates *Ptr or provides it, ScanFrom would be left at -/// begin() and this returns null. ScanFrom could also be left +/// The scan starts from \c ScanFrom. \c MaxInstsToScan specifies the maximum +/// instructions to scan in the block. If it is set to \c 0, it will scan the whole +/// block. /// -/// MaxInstsToScan specifies the maximum instructions to scan in the block. If -/// it is set to 0, it will scan the whole block. You can also optionally -/// specify an alias analysis implementation, which makes this more precise. +/// If the value is available, this function returns it. If not, it returns the +/// iterator for the last validated instruction that the value would be live +/// through. If we scanned the entire block and didn't find something that +/// invalidates \c *Ptr or provides it, \c ScanFrom is left at the last +/// instruction processed and this returns null. /// -/// If TBAATag is non-null and a load or store is found, the TBAA tag from the -/// load or store is recorded there. If there is no TBAA tag or if no access -/// is found, it is left unmodified. +/// You can also optionally specify an alias analysis implementation, which +/// makes this more precise. +/// +/// If \c AATags is non-null and a load or store is found, the AA tags from the +/// load or store are recorded there. If there are no AA tags or if no access is +/// found, it is left unmodified. Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan, - AliasAnalysis *AA, - MDNode **TBAATag) { - if (MaxInstsToScan == 0) MaxInstsToScan = ~0U; - - // If we're using alias analysis to disambiguate get the size of *Ptr. - uint64_t AccessSize = 0; - if (AA) { - Type *AccessTy = cast(Ptr->getType())->getElementType(); - AccessSize = AA->getTypeStoreSize(AccessTy); - } - + AliasAnalysis *AA, AAMDNodes *AATags) { + if (MaxInstsToScan == 0) + MaxInstsToScan = ~0U; + + Type *AccessTy = cast(Ptr->getType())->getElementType(); + + // Try to get the DataLayout for this module. This may be null, in which case + // the optimizations will be limited. + const DataLayout *DL = ScanBB->getDataLayout(); + + // Try to get the store size for the type. + uint64_t AccessSize = DL ? DL->getTypeStoreSize(AccessTy) + : AA ? AA->getTypeStoreSize(AccessTy) : 0; + + Value *StrippedPtr = Ptr->stripPointerCasts(); + while (ScanFrom != ScanBB->begin()) { // We must ignore debug info directives when counting (otherwise they // would affect codegen). @@ -159,62 +195,72 @@ Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, // Restore ScanFrom to expected value in case next test succeeds ScanFrom++; - + // Don't scan huge blocks. - if (MaxInstsToScan-- == 0) return nullptr; - + if (MaxInstsToScan-- == 0) + return nullptr; + --ScanFrom; // If this is a load of Ptr, the loaded value is available. // (This is true even if the load is volatile or atomic, although // those cases are unlikely.) if (LoadInst *LI = dyn_cast(Inst)) - if (AreEquivalentAddressValues(LI->getOperand(0), Ptr)) { - if (TBAATag) *TBAATag = LI->getMetadata(LLVMContext::MD_tbaa); + if (AreEquivalentAddressValues( + LI->getPointerOperand()->stripPointerCasts(), StrippedPtr) && + CastInst::isBitOrNoopPointerCastable(LI->getType(), AccessTy, DL)) { + if (AATags) + LI->getAAMetadata(*AATags); return LI; } - + if (StoreInst *SI = dyn_cast(Inst)) { + Value *StorePtr = SI->getPointerOperand()->stripPointerCasts(); // If this is a store through Ptr, the value is available! // (This is true even if the store is volatile or atomic, although // those cases are unlikely.) - if (AreEquivalentAddressValues(SI->getOperand(1), Ptr)) { - if (TBAATag) *TBAATag = SI->getMetadata(LLVMContext::MD_tbaa); + if (AreEquivalentAddressValues(StorePtr, StrippedPtr) && + CastInst::isBitOrNoopPointerCastable(SI->getValueOperand()->getType(), + AccessTy, DL)) { + if (AATags) + SI->getAAMetadata(*AATags); return SI->getOperand(0); } - - // If Ptr is an alloca and this is a store to a different alloca, ignore - // the store. This is a trivial form of alias analysis that is important - // for reg2mem'd code. - if ((isa(Ptr) || isa(Ptr)) && - (isa(SI->getOperand(1)) || - isa(SI->getOperand(1)))) + + // If both StrippedPtr and StorePtr reach all the way to an alloca or + // global and they are different, ignore the store. This is a trivial form + // of alias analysis that is important for reg2mem'd code. + if ((isa(StrippedPtr) || isa(StrippedPtr)) && + (isa(StorePtr) || isa(StorePtr)) && + StrippedPtr != StorePtr) continue; - + // If we have alias analysis and it says the store won't modify the loaded // value, ignore the store. if (AA && - (AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) + (AA->getModRefInfo(SI, StrippedPtr, AccessSize) & + AliasAnalysis::Mod) == 0) continue; - + // Otherwise the store that may or may not alias the pointer, bail out. ++ScanFrom; return nullptr; } - + // If this is some other instruction that may clobber Ptr, bail out. if (Inst->mayWriteToMemory()) { // If alias analysis claims that it really won't modify the load, // ignore it. if (AA && - (AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) + (AA->getModRefInfo(Inst, StrippedPtr, AccessSize) & + AliasAnalysis::Mod) == 0) continue; - + // May modify the pointer, bail out. ++ScanFrom; return nullptr; } } - + // Got to the start of the block, we didn't find it, but are done for this // block. return nullptr;