X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FBasicAliasAnalysis.cpp;h=f20e83e9113cdc6cf0c84e10bbc1ca3a5dd4e058;hb=55ec2218c448ef9e0d09b5534885b6d2a9786a73;hp=1d028c27b8c3257d8d21299c691c95250d909171;hpb=9e72a79ef4a9fcda482ce0b0e1f0bd6a4f16cffd;p=oota-llvm.git diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp index 1d028c27b8c..f20e83e9113 100644 --- a/lib/Analysis/BasicAliasAnalysis.cpp +++ b/lib/Analysis/BasicAliasAnalysis.cpp @@ -13,28 +13,28 @@ // //===----------------------------------------------------------------------===// -#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/Passes.h" -#include "llvm/Constants.h" -#include "llvm/DerivedTypes.h" -#include "llvm/Function.h" -#include "llvm/GlobalAlias.h" -#include "llvm/GlobalVariable.h" -#include "llvm/Instructions.h" -#include "llvm/IntrinsicInst.h" -#include "llvm/LLVMContext.h" -#include "llvm/Operator.h" -#include "llvm/Pass.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/CaptureTracking.h" -#include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Analysis/ValueTracking.h" -#include "llvm/Target/TargetData.h" -#include "llvm/Target/TargetLibraryInfo.h" -#include "llvm/ADT/SmallPtrSet.h" -#include "llvm/ADT/SmallVector.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GlobalAlias.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Operator.h" +#include "llvm/Pass.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/GetElementPtrTypeIterator.h" +#include "llvm/Target/TargetLibraryInfo.h" #include using namespace llvm; @@ -58,12 +58,12 @@ static bool isNonEscapingLocalObject(const Value *V) { // then it has not escaped before entering the function. Check if it escapes // inside the function. if (const Argument *A = dyn_cast(V)) - if (A->hasByValAttr() || A->hasNoAliasAttr()) { - // Don't bother analyzing arguments already known not to escape. - if (A->hasNoCaptureAttr()) - return true; + if (A->hasByValAttr() || A->hasNoAliasAttr()) + // Note even if the argument is marked nocapture we still need to check + // for copies made inside the function. The nocapture attribute only + // specifies that there are no copies made that outlive the function. return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); - } + return false; } @@ -84,10 +84,11 @@ static bool isEscapeSource(const Value *V) { /// getObjectSize - Return the size of the object specified by V, or /// UnknownSize if unknown. -static uint64_t getObjectSize(const Value *V, const TargetData &TD, +static uint64_t getObjectSize(const Value *V, const DataLayout &TD, + const TargetLibraryInfo &TLI, bool RoundToAlign = false) { uint64_t Size; - if (getObjectSize(V, Size, &TD, RoundToAlign)) + if (getObjectSize(V, Size, &TD, &TLI, RoundToAlign)) return Size; return AliasAnalysis::UnknownSize; } @@ -95,10 +96,40 @@ static uint64_t getObjectSize(const Value *V, const TargetData &TD, /// isObjectSmallerThan - Return true if we can prove that the object specified /// by V is smaller than Size. static bool isObjectSmallerThan(const Value *V, uint64_t Size, - const TargetData &TD) { + const DataLayout &TD, + const TargetLibraryInfo &TLI) { + // Note that the meanings of the "object" are slightly different in the + // following contexts: + // c1: llvm::getObjectSize() + // c2: llvm.objectsize() intrinsic + // c3: isObjectSmallerThan() + // c1 and c2 share the same meaning; however, the meaning of "object" in c3 + // refers to the "entire object". + // + // Consider this example: + // char *p = (char*)malloc(100) + // char *q = p+80; + // + // In the context of c1 and c2, the "object" pointed by q refers to the + // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20. + // + // However, in the context of c3, the "object" refers to the chunk of memory + // being allocated. So, the "object" has 100 bytes, and q points to the middle + // the "object". In case q is passed to isObjectSmallerThan() as the 1st + // parameter, before the llvm::getObjectSize() is called to get the size of + // entire object, we should: + // - either rewind the pointer q to the base-address of the object in + // question (in this case rewind to p), or + // - just give up. It is up to caller to make sure the pointer is pointing + // to the base address the object. + // + // We go for 2nd option for simplicity. + if (!isIdentifiedObject(V)) + return false; + // This function needs to use the aligned object size because we allow // reads a bit past the end given sufficient alignment. - uint64_t ObjectSize = getObjectSize(V, TD, /*RoundToAlign*/true); + uint64_t ObjectSize = getObjectSize(V, TD, TLI, /*RoundToAlign*/true); return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size; } @@ -106,11 +137,22 @@ static bool isObjectSmallerThan(const Value *V, uint64_t Size, /// isObjectSize - Return true if we can prove that the object specified /// by V has size Size. static bool isObjectSize(const Value *V, uint64_t Size, - const TargetData &TD) { - uint64_t ObjectSize = getObjectSize(V, TD); + const DataLayout &TD, const TargetLibraryInfo &TLI) { + uint64_t ObjectSize = getObjectSize(V, TD, TLI); return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size; } +/// isIdentifiedFunctionLocal - Return true if V is umabigously identified +/// at the function-level. Different IdentifiedFunctionLocals can't alias. +/// Further, an IdentifiedFunctionLocal can not alias with any function +/// arguments other than itself, which is not neccessarily true for +/// IdentifiedObjects. +static bool isIdentifiedFunctionLocal(const Value *V) +{ + return isa(V) || isNoAliasCall(V) || isNoAliasArgument(V); +} + + //===----------------------------------------------------------------------===// // GetElementPtr Instruction Decomposition and Analysis //===----------------------------------------------------------------------===// @@ -126,6 +168,15 @@ namespace { const Value *V; ExtensionKind Extension; int64_t Scale; + + bool operator==(const VariableGEPIndex &Other) const { + return V == Other.V && Extension == Other.Extension && + Scale == Other.Scale; + } + + bool operator!=(const VariableGEPIndex &Other) const { + return !operator==(Other); + } }; } @@ -140,7 +191,7 @@ namespace { /// represented in the result. static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, ExtensionKind &Extension, - const TargetData &TD, unsigned Depth) { + const DataLayout &TD, unsigned Depth) { assert(V->getType()->isIntegerTy() && "Not an integer value"); // Limit our recursion depth. @@ -215,14 +266,14 @@ static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, /// specified amount, but which may have other unrepresented high bits. As such, /// the gep cannot necessarily be reconstructed from its decomposed form. /// -/// When TargetData is around, this function is capable of analyzing everything +/// When DataLayout is around, this function is capable of analyzing everything /// that GetUnderlyingObject can look through. When not, it just looks /// through pointer casts. /// static const Value * DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, SmallVectorImpl &VarIndices, - const TargetData *TD) { + const DataLayout *TD) { // Limit recursion depth to limit compile time in crazy cases. unsigned MaxLookup = 6; @@ -266,7 +317,7 @@ DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, ->getElementType()->isSized()) return V; - // If we are lacking TargetData information, we can't compute the offets of + // If we are lacking DataLayout information, we can't compute the offets of // elements computed by GEPs. However, we can handle bitcast equivalent // GEPs. if (TD == 0) { @@ -417,13 +468,7 @@ namespace { /// BasicAliasAnalysis - This is the primary alias analysis implementation. struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis { static char ID; // Class identification, replacement for typeinfo - BasicAliasAnalysis() : ImmutablePass(ID), - // AliasCache rarely has more than 1 or 2 elements, - // so start it off fairly small so that clear() - // doesn't have to tromp through 64 (the default) - // elements on each alias query. This really wants - // something like a SmallDenseMap. - AliasCache(8) { + BasicAliasAnalysis() : ImmutablePass(ID) { initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry()); } @@ -443,7 +488,11 @@ namespace { "BasicAliasAnalysis doesn't support interprocedural queries."); AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag, LocB.Ptr, LocB.Size, LocB.TBAATag); - AliasCache.clear(); + // AliasCache rarely has more than 1 or 2 elements, always use + // shrink_and_clear so it quickly returns to the inline capacity of the + // SmallDenseMap if it ever grows larger. + // FIXME: This should really be shrink_to_inline_capacity_and_clear(). + AliasCache.shrink_and_clear(); return Alias; } @@ -481,7 +530,7 @@ namespace { private: // AliasCache - Track alias queries to guard against recursion. typedef std::pair LocPair; - typedef DenseMap AliasCacheTy; + typedef SmallDenseMap AliasCacheTy; AliasCacheTy AliasCache; // Visited - Track instructions visited by pointsToConstantMemory. @@ -490,6 +539,7 @@ namespace { // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP // instruction against another. AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size, + const MDNode *V1TBAAInfo, const Value *V2, uint64_t V2Size, const MDNode *V2TBAAInfo, const Value *UnderlyingV1, const Value *UnderlyingV2); @@ -621,7 +671,7 @@ BasicAliasAnalysis::getModRefBehavior(const Function *F) { // For intrinsics, we can check the table. if (unsigned iid = F->getIntrinsicID()) { #define GET_INTRINSIC_MODREF_BEHAVIOR -#include "llvm/Intrinsics.gen" +#include "llvm/IR/Intrinsics.gen" #undef GET_INTRINSIC_MODREF_BEHAVIOR } @@ -807,6 +857,21 @@ BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min); } +static bool areVarIndicesEqual(SmallVector &Indices1, + SmallVector &Indices2) { + unsigned Size1 = Indices1.size(); + unsigned Size2 = Indices2.size(); + + if (Size1 != Size2) + return false; + + for (unsigned I = 0; I != Size1; ++I) + if (Indices1[I] != Indices2[I]) + return false; + + return true; +} + /// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction /// against another pointer. We know that V1 is a GEP, but we don't know /// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, TD), @@ -814,6 +879,7 @@ BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, /// AliasAnalysis::AliasResult BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, + const MDNode *V1TBAAInfo, const Value *V2, uint64_t V2Size, const MDNode *V2TBAAInfo, const Value *UnderlyingV1, @@ -821,12 +887,44 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, int64_t GEP1BaseOffset; SmallVector GEP1VariableIndices; - // If we have two gep instructions with must-alias'ing base pointers, figure - // out if the indexes to the GEP tell us anything about the derived pointer. + // If we have two gep instructions with must-alias or not-alias'ing base + // pointers, figure out if the indexes to the GEP tell us anything about the + // derived pointer. if (const GEPOperator *GEP2 = dyn_cast(V2)) { // Do the base pointers alias? AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0, UnderlyingV2, UnknownSize, 0); + + // Check for geps of non-aliasing underlying pointers where the offsets are + // identical. + if ((BaseAlias == MayAlias) && V1Size == V2Size) { + // Do the base pointers alias assuming type and size. + AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size, + V1TBAAInfo, UnderlyingV2, + V2Size, V2TBAAInfo); + if (PreciseBaseAlias == NoAlias) { + // See if the computed offset from the common pointer tells us about the + // relation of the resulting pointer. + int64_t GEP2BaseOffset; + SmallVector GEP2VariableIndices; + const Value *GEP2BasePtr = + DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD); + const Value *GEP1BasePtr = + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. + if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { + assert(TD == 0 && + "DecomposeGEPExpression and GetUnderlyingObject disagree!"); + return MayAlias; + } + // Same offsets. + if (GEP1BaseOffset == GEP2BaseOffset && + areVarIndicesEqual(GEP1VariableIndices, GEP2VariableIndices)) + return NoAlias; + GEP1VariableIndices.clear(); + } + } // If we get a No or May, then return it immediately, no amount of analysis // will improve this situation. @@ -843,9 +941,8 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, const Value *GEP2BasePtr = DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD); - // If DecomposeGEPExpression isn't able to look all the way through the - // addressing operation, we must not have TD and this is too complex for us - // to handle without it. + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { assert(TD == 0 && "DecomposeGEPExpression and GetUnderlyingObject disagree!"); @@ -879,9 +976,8 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, const Value *GEP1BasePtr = DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); - // If DecomposeGEPExpression isn't able to look all the way through the - // addressing operation, we must not have TD and this is too complex for us - // to handle without it. + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. if (GEP1BasePtr != UnderlyingV1) { assert(TD == 0 && "DecomposeGEPExpression and GetUnderlyingObject disagree!"); @@ -1004,13 +1100,24 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, // on corresponding edges. if (const PHINode *PN2 = dyn_cast(V2)) if (PN2->getParent() == PN->getParent()) { - AliasResult Alias = - aliasCheck(PN->getIncomingValue(0), PNSize, PNTBAAInfo, - PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)), - V2Size, V2TBAAInfo); - if (Alias == MayAlias) - return MayAlias; - for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) { + LocPair Locs(Location(PN, PNSize, PNTBAAInfo), + Location(V2, V2Size, V2TBAAInfo)); + if (PN > V2) + std::swap(Locs.first, Locs.second); + // Analyse the PHIs' inputs under the assumption that the PHIs are + // NoAlias. + // If the PHIs are May/MustAlias there must be (recursively) an input + // operand from outside the PHIs' cycle that is MayAlias/MustAlias or + // there must be an operation on the PHIs within the PHIs' value cycle + // that causes a MayAlias. + // Pretend the phis do not alias. + AliasResult Alias = NoAlias; + assert(AliasCache.count(Locs) && + "There must exist an entry for the phi node"); + AliasResult OrigAliasResult = AliasCache[Locs]; + AliasCache[Locs] = NoAlias; + + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { AliasResult ThisAlias = aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo, PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), @@ -1019,6 +1126,11 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, if (Alias == MayAlias) break; } + + // Reset if speculation failed. + if (Alias != NoAlias) + AliasCache[Locs] = OrigAliasResult; + return Alias; } @@ -1104,10 +1216,10 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, (isa(O2) && isIdentifiedObject(O1) && !isa(O1))) return NoAlias; - // Arguments can't alias with local allocations or noalias calls - // in the same function. - if (((isa(O1) && (isa(O2) || isNoAliasCall(O2))) || - (isa(O2) && (isa(O1) || isNoAliasCall(O1))))) + // Function arguments can't alias with things that are known to be + // unambigously identified at the function level. + if ((isa(O1) && isIdentifiedFunctionLocal(O2)) || + (isa(O2) && isIdentifiedFunctionLocal(O1))) return NoAlias; // Most objects can't alias null. @@ -1133,8 +1245,8 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, // If the size of one access is larger than the entire object on the other // side, then we know such behavior is undefined and can assume no alias. if (TD) - if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD)) || - (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD))) + if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD, *TLI)) || + (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD, *TLI))) return NoAlias; // Check the cache before climbing up use-def chains. This also terminates @@ -1154,15 +1266,17 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, std::swap(V1, V2); std::swap(V1Size, V2Size); std::swap(O1, O2); + std::swap(V1TBAAInfo, V2TBAAInfo); } if (const GEPOperator *GV1 = dyn_cast(V1)) { - AliasResult Result = aliasGEP(GV1, V1Size, V2, V2Size, V2TBAAInfo, O1, O2); + AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, O1, O2); if (Result != MayAlias) return AliasCache[Locs] = Result; } if (isa(V2) && !isa(V1)) { std::swap(V1, V2); std::swap(V1Size, V2Size); + std::swap(V1TBAAInfo, V2TBAAInfo); } if (const PHINode *PN = dyn_cast(V1)) { AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo, @@ -1173,6 +1287,7 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, if (isa(V2) && !isa(V1)) { std::swap(V1, V2); std::swap(V1Size, V2Size); + std::swap(V1TBAAInfo, V2TBAAInfo); } if (const SelectInst *S1 = dyn_cast(V1)) { AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo, @@ -1184,8 +1299,8 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, // accesses is accessing the entire object, then the accesses must // overlap in some way. if (TD && O1 == O2) - if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD)) || - (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD))) + if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD, *TLI)) || + (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD, *TLI))) return AliasCache[Locs] = PartialAlias; AliasResult Result =