[DAGCombiner] Fix PR25763 - vector comparison constant folding + sign-extension

PR25763 demonstrated an issue with D14683 - vector comparison constant folding only works for i1 results, so we need to split off the sign-extension of the result to the required type. Luckily this can be done with the existing type legalization code.

llvm-svn: 255289

1 files changed, 8 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 771bb00d86a..4596b8eba1a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3338,12 +3338,15 @@ SDValue SelectionDAG::FoldConstantVectorArithmetic(unsigned Opcode, SDLoc DL,
       !std::all_of(Ops.begin(), Ops.end(), IsScalarOrSameVectorSize))
     return SDValue();
 
+  // If we are comparing vectors, then the result needs to be a i1 boolean
+  // that is then sign-extended back to the legal result type.
+  EVT SVT = (Opcode == ISD::SETCC ? MVT::i1 : VT.getScalarType());
+
   // Find legal integer scalar type for constant promotion and
   // ensure that its scalar size is at least as large as source.
-  EVT SVT = VT.getScalarType();
-  EVT LegalSVT = SVT;
-  if (SVT.isInteger()) {
-    LegalSVT = TLI->getTypeToTransformTo(*getContext(), SVT);
+  EVT LegalSVT = VT.getScalarType();
+  if (LegalSVT.isInteger()) {
+    LegalSVT = TLI->getTypeToTransformTo(*getContext(), LegalSVT);
     if (LegalSVT.bitsLT(SVT))
       return SDValue();
   }
@@ -3380,7 +3383,7 @@ SDValue SelectionDAG::FoldConstantVectorArithmetic(unsigned Opcode, SDLoc DL,
 
     // Legalize the (integer) scalar constant if necessary.
     if (LegalSVT != SVT)
-      ScalarResult = getNode(ISD::ANY_EXTEND, DL, LegalSVT, ScalarResult);
+      ScalarResult = getNode(ISD::SIGN_EXTEND, DL, LegalSVT, ScalarResult);
 
     // Scalar folding only succeeded if the result is a constant or UNDEF.
     if (ScalarResult.getOpcode() != ISD::UNDEF &&