[PATCH] D29216: Fix BasicAA incorrect assumption on GEP

[Mehdi AMINI via Phabricator via llvm-commits]

mehdi_amini updated this revision to Diff 86027.
mehdi_amini added a comment.

Update after discussing with Chandler on IRC: making the query unsized should be enough here!

If we deduce NoAlias with an unsized query, it should mean that a GEP can't
reach one allocation from another.


https://reviews.llvm.org/D29216

Files:
  llvm/lib/Analysis/BasicAliasAnalysis.cpp
  llvm/test/Analysis/BasicAA/pr31761.ll
  llvm/test/Transforms/SLPVectorizer/X86/tiny-tree.ll


Index: llvm/test/Transforms/SLPVectorizer/X86/tiny-tree.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/X86/tiny-tree.ll
+++ llvm/test/Transforms/SLPVectorizer/X86/tiny-tree.ll
@@ -2,7 +2,6 @@
 target triple = "x86_64-apple-macosx10.8.0"
 ; RUN: opt < %s -basicaa -slp-vectorizer -S -mtriple=x86_64-apple-macosx10.8.0 -mcpu=corei7 | FileCheck %s
 
-
 ; CHECK: tiny_tree_fully_vectorizable
 ; CHECK: load <2 x double>
 ; CHECK: store <2 x double>
Index: llvm/test/Analysis/BasicAA/pr31761.ll
===================================================================
--- /dev/null
+++ llvm/test/Analysis/BasicAA/pr31761.ll
@@ -0,0 +1,19 @@
+; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
+
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.12.0"
+
+%struct.blam = type { i32, i32 }
+
+
+; CHECK-DAG: MayAlias: i32* %tmp, i32* %tmp3
+
+define i1 @ham(%struct.blam* %arg)  {
+  %isNull = icmp eq %struct.blam* %arg, null
+  %tmp = getelementptr  %struct.blam, %struct.blam* %arg, i64 0, i32 0
+  %tmp2 = getelementptr  %struct.blam, %struct.blam* %arg, i64 0, i32 1
+  %select = select i1 %isNull, i32* null, i32* %tmp2
+  %tmp3 = getelementptr  i32, i32* %select, i32 -1
+  ret i1 true
+}
Index: llvm/lib/Analysis/BasicAliasAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -1191,14 +1191,14 @@
       return MayAlias;
 
     AliasResult R = aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize,
-                               AAMDNodes(), V2, V2Size, V2AAInfo,
-                               nullptr, UnderlyingV2);
+                               AAMDNodes(), V2, MemoryLocation::UnknownSize,
+                               V2AAInfo, nullptr, UnderlyingV2);
     if (R != MustAlias)
       // If V2 may alias GEP base pointer, conservatively returns MayAlias.
       // If V2 is known not to alias GEP base pointer, then the two values
-      // cannot alias per GEP semantics: "A pointer value formed from a
-      // getelementptr instruction is associated with the addresses associated
-      // with the first operand of the getelementptr".
+      // cannot alias per GEP semantics: "Any memory access must be done through
+      // a pointer value associated with an address range of the memory access,
+      // otherwise the behavior is undefined.".
       return R;
 
     // If the max search depth is reached the result is undefined


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