diff options
| -rw-r--r-- | lib/Analysis/BasicAliasAnalysis.cpp | 74 | ||||
| -rw-r--r-- | test/Analysis/BasicAA/noalias-geps.ll | 54 |
2 files changed, 119 insertions, 9 deletions
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp index a3e6575865..d537d63317 100644 --- a/lib/Analysis/BasicAliasAnalysis.cpp +++ b/lib/Analysis/BasicAliasAnalysis.cpp @@ -128,6 +128,15 @@ 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); + } }; } @@ -490,6 +499,7 @@ 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); @@ -807,6 +817,21 @@ BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min); } +static bool areVarIndicesEqual(SmallVector<VariableGEPIndex, 4> &Indices1, + SmallVector<VariableGEPIndex, 4> &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 +839,7 @@ 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, @@ -821,9 +847,41 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, int64_t GEP1BaseOffset; SmallVector<VariableGEPIndex, 4> 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<GEPOperator>(V2)) { + // Check for geps of non-aliasing underlying pointers where the offsets are + // identical. + if (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<VariableGEPIndex, 4> 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 TargetData. + 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(); + } + } + // Do the base pointers alias? AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0, UnderlyingV2, UnknownSize, 0); @@ -843,9 +901,8 @@ 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 TargetData. if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { assert(TD == 0 && "DecomposeGEPExpression and GetUnderlyingObject disagree!"); @@ -879,9 +936,8 @@ 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 TargetData. if (GEP1BasePtr != UnderlyingV1) { assert(TD == 0 && "DecomposeGEPExpression and GetUnderlyingObject disagree!"); @@ -1156,7 +1212,7 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, std::swap(O1, O2); } if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(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; } diff --git a/test/Analysis/BasicAA/noalias-geps.ll b/test/Analysis/BasicAA/noalias-geps.ll new file mode 100644 index 0000000000..a93d778da0 --- /dev/null +++ b/test/Analysis/BasicAA/noalias-geps.ll @@ -0,0 +1,54 @@ +; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s + +target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128" + +; Check that geps with equal base offsets of noalias base pointers stay noalias. +define i32 @test(i32* %p, i16 %i) { + %pi = getelementptr i32* %p, i32 0 + %pi.next = getelementptr i32* %p, i32 1 + %b = icmp eq i16 %i, 0 + br i1 %b, label %bb1, label %bb2 + +bb1: + %f = getelementptr i32* %pi, i32 1 + %g = getelementptr i32* %pi.next, i32 1 + br label %bb3 +bb2: + %f2 = getelementptr i32* %pi, i32 1 + %g2 = getelementptr i32* %pi.next, i32 1 + br label %bb3 + +bb3: + %ptr_phi = phi i32* [ %f, %bb1 ], [ %f2, %bb2 ] + %ptr_phi2 = phi i32* [ %g, %bb1 ], [ %g2, %bb2 ] +; CHECK: NoAlias: i32* %f1, i32* %g1 + %f1 = getelementptr i32* %ptr_phi , i32 1 + %g1 = getelementptr i32* %ptr_phi2 , i32 1 + +ret i32 0 +} + +; Check that geps with equal indices of noalias base pointers stay noalias. +define i32 @test2([2 x i32]* %p, i32 %i) { + %pi = getelementptr [2 x i32]* %p, i32 0 + %pi.next = getelementptr [2 x i32]* %p, i32 1 + %b = icmp eq i32 %i, 0 + br i1 %b, label %bb1, label %bb2 + +bb1: + %f = getelementptr [2 x i32]* %pi, i32 1 + %g = getelementptr [2 x i32]* %pi.next, i32 1 + br label %bb3 +bb2: + %f2 = getelementptr [2 x i32]* %pi, i32 1 + %g2 = getelementptr [2 x i32]* %pi.next, i32 1 + br label %bb3 +bb3: + %ptr_phi = phi [2 x i32]* [ %f, %bb1 ], [ %f2, %bb2 ] + %ptr_phi2 = phi [2 x i32]* [ %g, %bb1 ], [ %g2, %bb2 ] +; CHECK: NoAlias: i32* %f1, i32* %g1 + %f1 = getelementptr [2 x i32]* %ptr_phi , i32 1, i32 %i + %g1 = getelementptr [2 x i32]* %ptr_phi2 , i32 1, i32 %i + +ret i32 0 +} |