[PATCH] D83163: [DAGCombiner] visitSIGN_EXTEND_INREG should fold sext_vector_inreg(undef) to 0 not undef.

[Craig Topper via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG76123d338dc5: [DAGCombiner] visitSIGN_EXTEND_INREG should fold sext_vector_inreg(undef) to 0… (authored by craig.topper).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D83163/new/

https://reviews.llvm.org/D83163

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp


Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10957,8 +10957,9 @@
   unsigned VTBits = VT.getScalarSizeInBits();
   unsigned ExtVTBits = ExtVT.getScalarSizeInBits();
 
+  // sext_vector_inreg(undef) = 0 because the top bit will all be the same.
   if (N0.isUndef())
-    return DAG.getUNDEF(VT);
+    return DAG.getConstant(0, SDLoc(N), VT);
 
   // fold (sext_in_reg c1) -> c1
   if (DAG.isConstantIntBuildVectorOrConstantInt(N0))


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