[PATCH] D91482: [BasicAA] Remove unnecessary known size requirement

[Nikita Popov via Phabricator via llvm-commits]

nikic updated this revision to Diff 306722.
nikic edited the summary of this revision.
nikic added a comment.

Rebase over D91649 <https://reviews.llvm.org/D91649>, after which this correctness of this change should be more obvious. At this point in BasicAA, all LocationSizes only allow access after the base pointer.

The changes to MemorySSA tests are now gone.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D91482/new/

https://reviews.llvm.org/D91482

Files:
  llvm/lib/Analysis/BasicAliasAnalysis.cpp
  llvm/test/Analysis/BasicAA/negoffset.ll


Index: llvm/test/Analysis/BasicAA/negoffset.ll
===================================================================
--- llvm/test/Analysis/BasicAA/negoffset.ll
+++ llvm/test/Analysis/BasicAA/negoffset.ll
@@ -117,3 +117,13 @@
   %2 = load i32, i32* %1
   ret i32 %2
 }
+
+; CHECK-LABEL: Function: one_size_unknown:
+; CHECK: NoModRef:  Ptr: i8* %p.minus1	<->  call void @llvm.memset.p0i8.i32(i8* %p, i8 0, i32 %size, i1 false)
+define void @one_size_unknown(i8* %p, i32 %size) {
+  %p.minus1 = getelementptr inbounds i8, i8* %p, i32 -1
+  call void @llvm.memset.p0i8.i32(i8* %p, i8 0, i32 %size, i1 false)
+  ret void
+}
+
+declare void @llvm.memset.p0i8.i32(i8*, i8, i32, i1)
Index: llvm/lib/Analysis/BasicAliasAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -1345,9 +1345,7 @@
       // ---------------->|
       // |-->V1Size       |-------> V2Size
       // GEP1             V2
-      // We need to know that V2Size is not unknown, otherwise we might have
-      // stripped a gep with negative index ('gep <ptr>, -1, ...).
-      if (V1Size.hasValue() && V2Size.hasValue()) {
+      if (V1Size.hasValue()) {
         if ((-GEP1BaseOffset).ult(V1Size.getValue()))
           return PartialAlias;
         return NoAlias;


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