[X86][SSE] Add UNDEF handling to combineSelect ISD::USUBSAT matching (PR40083)

llvm-svn: 352330

1 files changed, 7 insertions, 5 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index e0830df512b..ffe64f129bb 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -34520,14 +34520,16 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
           // If the RHS is a constant we have to reverse the const
           // canonicalization.
           // x > C-1 ? x+-C : 0 --> subus x, C
-          // TODO: Handle build_vectors with undef elements.
           auto MatchUSUBSAT = [](ConstantSDNode *Op, ConstantSDNode *Cond) {
-            return Cond->getAPIntValue() == (-Op->getAPIntValue() - 1);
+            return (!Op && !Cond) ||
+                   (Op && Cond &&
+                    Cond->getAPIntValue() == (-Op->getAPIntValue() - 1));
           };
           if (CC == ISD::SETUGT && Other->getOpcode() == ISD::ADD &&
-              ISD::matchBinaryPredicate(OpRHS, CondRHS, MatchUSUBSAT)) {
-            OpRHS = DAG.getNode(ISD::SUB, DL, VT,
-                                DAG.getConstant(0, DL, VT), OpRHS);
+              ISD::matchBinaryPredicate(OpRHS, CondRHS, MatchUSUBSAT,
+                                        /*AllowUndefs*/ true)) {
+            OpRHS = DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT),
+                                OpRHS);
             return DAG.getNode(ISD::USUBSAT, DL, VT, OpLHS, OpRHS);
           }