[llvm-commits] [llvm] r163317 - in /llvm/trunk: lib/Analysis/BasicAliasAnalysis.cpp test/Analysis/BasicAA/noalias-geps.ll
Arnold Schwaighofer
arnolds at codeaurora.org
Thu Sep 6 07:31:52 PDT 2012
Author: arnolds
Date: Thu Sep 6 09:31:51 2012
New Revision: 163317
URL: http://llvm.org/viewvc/llvm-project?rev=163317&view=rev
Log:
BasicAA: GEPs of NoAlias'ing base ptr with equivalent indices are NoAlias
If we can show that the base pointers of two GEPs don't alias each other using
precise analysis and the indices and base offset are equal then the two GEPs
also don't alias each other.
This is primarily needed for the follow up patch that analyses NoAlias'ing PHI
nodes.
Part 1/2 of fix for PR13564.
Added:
llvm/trunk/test/Analysis/BasicAA/noalias-geps.ll
Modified:
llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=163317&r1=163316&r2=163317&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Thu Sep 6 09:31:51 2012
@@ -128,6 +128,15 @@
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 @@
// 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 @@
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 @@
///
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 @@
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 @@
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 @@
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 @@
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;
}
Added: llvm/trunk/test/Analysis/BasicAA/noalias-geps.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/noalias-geps.ll?rev=163317&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/BasicAA/noalias-geps.ll (added)
+++ llvm/trunk/test/Analysis/BasicAA/noalias-geps.ll Thu Sep 6 09:31:51 2012
@@ -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
+}
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