[PATCH] D33449: [InstCombine] Fix extractelement use before def

[Sven van Haastregt via Phabricator via llvm-commits]

svenvh created this revision.

This fixes a bug that can cause extractelements with operands that
haven't been defined yet to be inserted at a wrong point when
optimising insertelements.

Patch by Karl Hylen.


https://reviews.llvm.org/D33449

Files:
  lib/Transforms/InstCombine/InstCombineVectorOps.cpp
  test/Transforms/InstCombine/insert-extract-shuffle.ll


Index: test/Transforms/InstCombine/insert-extract-shuffle.ll
===================================================================
--- test/Transforms/InstCombine/insert-extract-shuffle.ll
+++ test/Transforms/InstCombine/insert-extract-shuffle.ll
@@ -260,3 +260,20 @@
   %ins2 = insertelement <4 x float> %ins1, float %ext1, i32 3
   ret <4 x float> %ins2
 }
+
+; Don't insert extractelements from the wider vector before the def of the index operand.
+; CHECK-LABEL: @extractelt_insertion
+; CHECK: %0 = shufflevector
+; CHECK: %b = shufflevector
+; CHECK: %c = add
+; CHECK: %1 = extractelement <4 x i32> %0, i32 %c
+define <4 x i32> @extractelt_insertion(<2 x i32> %x, i32 %y) {
+entry:
+  %a = extractelement <2 x i32> %x, i32 1
+  %b = insertelement <4 x i32> zeroinitializer, i32 %a, i64 3
+  %c = add i32 %y, 3
+  %d = extractelement <2 x i32> %x, i32 %c
+  %e = icmp eq i32 %d, 0
+  %ret = select i1 %e, <4 x i32> %b, <4 x i32> zeroinitializer
+  ret <4 x i32> %ret
+}
Index: lib/Transforms/InstCombine/InstCombineVectorOps.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -440,7 +440,7 @@
     if (!OldExt || OldExt->getParent() != WideVec->getParent())
       continue;
     auto *NewExt = ExtractElementInst::Create(WideVec, OldExt->getOperand(1));
-    NewExt->insertAfter(WideVec);
+    NewExt->insertAfter(OldExt);
     IC.replaceInstUsesWith(*OldExt, NewExt);
   }
 }


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