[PATCH] D40231: InstructionSimplify: 'extractelement' with an undef index is undef

[Zvi Rackover via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL319910: InstructionSimplify: 'extractelement' with an undef index is undef (authored by zvi).

Repository:
  rL LLVM

https://reviews.llvm.org/D40231

Files:
  llvm/trunk/lib/Analysis/InstructionSimplify.cpp
  llvm/trunk/test/Transforms/InstSimplify/2011-09-05-InsertExtractValue.ll


Index: llvm/trunk/test/Transforms/InstSimplify/2011-09-05-InsertExtractValue.ll
===================================================================
--- llvm/trunk/test/Transforms/InstSimplify/2011-09-05-InsertExtractValue.ll
+++ llvm/trunk/test/Transforms/InstSimplify/2011-09-05-InsertExtractValue.ll
@@ -46,3 +46,10 @@
 ; CHECK-NEXT: %[[extract:.*]] = extractelement <8 x i8> %[[add]], i32 6
 ; CHECK-NEXT: ret i8 %[[extract]]
 }
+
+define i32 @test5(<4 x i32> %V) {
+  %extract = extractelement <4 x i32> %V, i32 undef
+  ret i32 %extract
+}
+; CHECK-LABEL: @test5(
+; CHECK: ret i32 undef
Index: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp
@@ -3901,6 +3901,11 @@
     if (Value *Elt = findScalarElement(Vec, IdxC->getZExtValue()))
       return Elt;
 
+  // An undef extract index can be arbitrarily chosen to be an out-of-range
+  // index value, which would result in the instruction being undef.
+  if (isa<UndefValue>(Idx))
+    return UndefValue::get(Vec->getType()->getVectorElementType());
+
   return nullptr;
 }
 


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