[DAGCombiner] Rewrite r331896 in a different way to address a FIXME. NFCI

llvm-svn: 342809

1 files changed, 14 insertions, 11 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 88d5e78ff1e..0493fde5fa2 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9852,17 +9852,20 @@ SDValue DAGCombiner::visitBITCAST(SDNode *N) {
   }
 
   // If the input is a constant, let getNode fold it.
-  // We always need to check that this is just a fp -> int or int -> conversion
-  // otherwise we will get back N which will confuse the caller into thinking
-  // we used CombineTo. This can block target combines from running. If we can't
-  // allowed legal operations, we need to ensure the resulting operation will be
-  // legal.
-  // TODO: Maybe we should check that the return value isn't N explicitly?
-  if ((isa<ConstantSDNode>(N0) && VT.isFloatingPoint() && !VT.isVector() &&
-       (!LegalOperations || TLI.isOperationLegal(ISD::ConstantFP, VT))) ||
-      (isa<ConstantFPSDNode>(N0) && VT.isInteger() && !VT.isVector() &&
-       (!LegalOperations || TLI.isOperationLegal(ISD::Constant, VT))))
-    return DAG.getBitcast(VT, N0);
+  if (isa<ConstantSDNode>(N0) || isa<ConstantFPSDNode>(N0)) {
+    // If we can't allow illegal operations, we need to check that this is just
+    // a fp -> int or int -> conversion and that the resulting operation will
+    // be legal.
+    if (!LegalOperations ||
+        (isa<ConstantSDNode>(N0) && VT.isFloatingPoint() && !VT.isVector() &&
+         TLI.isOperationLegal(ISD::ConstantFP, VT)) ||
+        (isa<ConstantFPSDNode>(N0) && VT.isInteger() && !VT.isVector() &&
+         TLI.isOperationLegal(ISD::Constant, VT))) {
+      SDValue C = DAG.getBitcast(VT, N0);
+      if (C.getNode() != N)
+        return C;
+    }
+  }
 
   // (conv (conv x, t1), t2) -> (conv x, t2)
   if (N0.getOpcode() == ISD::BITCAST)