X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FLoads.cpp;h=4b2fa3c6505a14a1e0b4a5a1eacc9abe5aa7cab6;hb=92989cbe8452a9406f6e0d3c5709b5745f27158a;hp=1c3e281dffb0163d5603b04f1fb831f24b12f6ca;hpb=e99ca835bc15dbfda5b3eae0579a1451201c8349;p=oota-llvm.git diff --git a/lib/Analysis/Loads.cpp b/lib/Analysis/Loads.cpp index 1c3e281dffb..4b2fa3c6505 100644 --- a/lib/Analysis/Loads.cpp +++ b/lib/Analysis/Loads.cpp @@ -19,6 +19,7 @@ #include "llvm/IR/GlobalVariable.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Module.h" #include "llvm/IR/Operator.h" using namespace llvm; @@ -35,15 +36,16 @@ using namespace llvm; /// 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; @@ -52,15 +54,26 @@ 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 = ScanFrom->getModule()->getDataLayout(); + + // Zero alignment means that the load has the ABI alignment for the target + if (Align == 0) + Align = DL.getABITypeAlignment(V->getType()->getPointerElementType()); + assert(isPowerOf2_32(Align)); + 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; @@ -72,27 +85,30 @@ 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(); } } + PointerType *AddrTy = cast(V->getType()); + uint64_t LoadSize = DL.getTypeStoreSize(AddrTy->getElementType()); + + // 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. if (BaseType && BaseType->isSized()) { - if (TD && BaseAlign == 0) - BaseAlign = TD->getPrefTypeAlignment(BaseType); + if (BaseAlign == 0) + BaseAlign = DL.getPrefTypeAlignment(BaseType); if (Align <= BaseAlign) { - if (!TD) - return true; // Loading directly from an alloca or global is OK. - // 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) && - (Align == 0 || (ByteOffset % Align) == 0)) + if (ByteOffset + LoadSize <= DL.getTypeAllocSize(BaseType) && + ((ByteOffset % Align) == 0)) return true; } } @@ -102,7 +118,12 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom, // from/to. If so, the previous load or store would have already trapped, // so there is no harm doing an extra load (also, CSE will later eliminate // the load entirely). - BasicBlock::iterator BBI = ScanFrom, E = ScanFrom->getParent()->begin(); + BasicBlock::iterator BBI = ScanFrom->getIterator(), + 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; @@ -113,15 +134,46 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom, !isa(BBI)) return false; + Value *AccessedPtr; + unsigned AccessedAlign; if (LoadInst *LI = dyn_cast(BBI)) { - if (AreEquivalentAddressValues(LI->getOperand(0), V)) return true; + AccessedPtr = LI->getPointerOperand(); + AccessedAlign = LI->getAlignment(); } else if (StoreInst *SI = dyn_cast(BBI)) { - if (AreEquivalentAddressValues(SI->getOperand(1), V)) return true; - } + AccessedPtr = SI->getPointerOperand(); + AccessedAlign = SI->getAlignment(); + } else + continue; + + Type *AccessedTy = AccessedPtr->getType()->getPointerElementType(); + if (AccessedAlign == 0) + AccessedAlign = DL.getABITypeAlignment(AccessedTy); + if (AccessedAlign < Align) + continue; + + // Handle trivial cases. + if (AccessedPtr == V) + return true; + + if (AreEquivalentAddressValues(AccessedPtr->stripPointerCasts(), V) && + LoadSize <= DL.getTypeStoreSize(AccessedTy)) + return true; } return false; } +/// DefMaxInstsToScan - the default number of maximum instructions +/// to scan in the block, used by FindAvailableLoadedValue(). +/// FindAvailableLoadedValue() was introduced in r60148, to improve jump +/// threading in part by eliminating partially redundant loads. +/// At that point, the value of MaxInstsToScan was already set to '6' +/// without documented explanation. +cl::opt +llvm::DefMaxInstsToScan("available-load-scan-limit", cl::init(6), cl::Hidden, + cl::desc("Use this to specify the default maximum number of instructions " + "to scan backward from a given instruction, when searching for " + "available loaded value")); + /// \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. /// @@ -148,17 +200,19 @@ Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, 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); - } + Type *AccessTy = cast(Ptr->getType())->getElementType(); + + const DataLayout &DL = ScanBB->getModule()->getDataLayout(); + + // Try to get the store size for the type. + uint64_t AccessSize = DL.getTypeStoreSize(AccessTy); + + Value *StrippedPtr = Ptr->stripPointerCasts(); while (ScanFrom != ScanBB->begin()) { // We must ignore debug info directives when counting (otherwise they // would affect codegen). - Instruction *Inst = --ScanFrom; + Instruction *Inst = &*--ScanFrom; if (isa(Inst)) continue; @@ -174,34 +228,38 @@ Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, // (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 (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 (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) + if (AA && (AA->getModRefInfo(SI, StrippedPtr, AccessSize) & MRI_Mod) == 0) continue; // Otherwise the store that may or may not alias the pointer, bail out. @@ -214,7 +272,7 @@ Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, // 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) & MRI_Mod) == 0) continue; // May modify the pointer, bail out.