Add trunc (select c, a, b) -> select c (trunc a), (trunc b) combine.

Do this if the truncate is free and the select is legal.

llvm-svn: 212640

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 7497feb1e66..ab07954a6f1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6013,6 +6013,20 @@ SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
     }
   }
 
+  // trunc (select c, a, b) -> select c, (trunc a), (trunc b)
+  if (N0.getOpcode() == ISD::SELECT) {
+    EVT SrcVT = N0.getValueType();
+    if ((!LegalOperations || TLI.isOperationLegal(ISD::SELECT, SrcVT)) &&
+        TLI.isTruncateFree(SrcVT, VT)) {
+      SDLoc SL(N0);
+      SDValue TruncOp0 = DAG.getNode(ISD::TRUNCATE, SL, VT, N0.getOperand(1));
+      SDValue TruncOp1 = DAG.getNode(ISD::TRUNCATE, SL, VT, N0.getOperand(2));
+      EVT SetCCVT = getSetCCResultType(VT);
+      SDValue Cond = DAG.getSExtOrTrunc(N0.getOperand(0), SL, SetCCVT);
+      return DAG.getNode(ISD::SELECT, SDLoc(N), VT, Cond, TruncOp0, TruncOp1);
+    }
+  }
+
   // Fold a series of buildvector, bitcast, and truncate if possible.
   // For example fold
   //   (2xi32 trunc (bitcast ((4xi32)buildvector x, x, y, y) 2xi64)) to