[x86] try select simplification for target-specific nodes

This failed to select (which might be a separate bug) in
X86ISelDAGToDAG because we try to create a select node
that can be simplified away after rL347227.

This change avoids the problem by simplifying the SHRUNKBLEND
node sooner. In the test case, we manage to realize that the
true/false values of the select (SHRUNKBLEND) are the same thing,
so it simplifies away completely.

llvm-svn: 347818

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 8e487a08376..37748e1c400 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -33674,9 +33674,14 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
                              const X86Subtarget &Subtarget) {
   SDLoc DL(N);
   SDValue Cond = N->getOperand(0);
-  // Get the LHS/RHS of the select.
   SDValue LHS = N->getOperand(1);
   SDValue RHS = N->getOperand(2);
+
+  // Try simplification again because we use this function to optimize
+  // SHRUNKBLEND nodes that are not handled by the generic combiner.
+  if (SDValue V = DAG.simplifySelect(Cond, LHS, RHS))
+    return V;
+
   EVT VT = LHS.getValueType();
   EVT CondVT = Cond.getValueType();
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();