[PATCH] D109012: [SLPVectorizer] Make aliasing check more precise

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: ABataev, anton-afanasyev, spatel.
Herald added subscribers: jeroen.dobbelaere, hiraditya.
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SLPVectorizer currently uses AA::isNoAlias() to determine whether two locations alias. This does not work if one of the instructions is a call. Instead, we should check getModRefInfo(), which determines whether an arbitrary modified or references a given location.

Among other things, this prevents `@llvm.experimental.noalias.scope.decl()` and other inaccessiblmemonly intrinsics from interfering with SLP vectorization.


https://reviews.llvm.org/D109012

Files:
  llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
  llvm/test/Transforms/SLPVectorizer/int_sideeffect.ll


Index: llvm/test/Transforms/SLPVectorizer/int_sideeffect.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/int_sideeffect.ll
+++ llvm/test/Transforms/SLPVectorizer/int_sideeffect.ll
@@ -44,16 +44,12 @@
 ; CHECK-NEXT:    [[P1:%.*]] = getelementptr float, float* [[P]], i64 1
 ; CHECK-NEXT:    [[P2:%.*]] = getelementptr float, float* [[P]], i64 2
 ; CHECK-NEXT:    [[P3:%.*]] = getelementptr float, float* [[P]], i64 3
-; CHECK-NEXT:    [[L0:%.*]] = load float, float* [[P0]], align 4
-; CHECK-NEXT:    [[L1:%.*]] = load float, float* [[P1]], align 4
-; CHECK-NEXT:    [[L2:%.*]] = load float, float* [[P2]], align 4
 ; CHECK-NEXT:    call void @foo() #[[ATTR1:[0-9]+]]
-; CHECK-NEXT:    [[L3:%.*]] = load float, float* [[P3]], align 4
-; CHECK-NEXT:    store float [[L0]], float* [[P0]], align 4
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast float* [[P0]] to <4 x float>*
+; CHECK-NEXT:    [[TMP2:%.*]] = load <4 x float>, <4 x float>* [[TMP1]], align 4
 ; CHECK-NEXT:    call void @foo() #[[ATTR1]]
-; CHECK-NEXT:    store float [[L1]], float* [[P1]], align 4
-; CHECK-NEXT:    store float [[L2]], float* [[P2]], align 4
-; CHECK-NEXT:    store float [[L3]], float* [[P3]], align 4
+; CHECK-NEXT:    [[TMP3:%.*]] = bitcast float* [[P0]] to <4 x float>*
+; CHECK-NEXT:    store <4 x float> [[TMP2]], <4 x float>* [[TMP3]], align 4
 ; CHECK-NEXT:    ret void
 ;
   %p0 = getelementptr float, float* %p, i64 0
Index: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -1965,12 +1965,9 @@
     if (result.hasValue()) {
       return result.getValue();
     }
-    MemoryLocation Loc2 = getLocation(Inst2, AA);
     bool aliased = true;
-    if (Loc1.Ptr && Loc2.Ptr && isSimple(Inst1) && isSimple(Inst2)) {
-      // Do the alias check.
-      aliased = !AA->isNoAlias(Loc1, Loc2);
-    }
+    if (Loc1.Ptr && isSimple(Inst1))
+      aliased = isModOrRefSet(AA->getModRefInfo(Inst2, Loc1));
     // Store the result in the cache.
     result = aliased;
     return aliased;


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