[DAGCombiner] move fadd simplification ahead of other folds

  
I don't know if it's possible to expose this diff in a test,
but we should always try simplifications (no new nodes created)
before more complicated transforms for efficiency (similar to
what we do in IR).

llvm-svn: 339298

1 files changed, 6 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 2196e813bdf..9690d2c205a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10745,6 +10745,12 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
   if (N0CFP && !N1CFP)
     return DAG.getNode(ISD::FADD, DL, VT, N1, N0, Flags);
 
+  // N0 + -0.0 --> N0 (also allowed with +0.0 and fast-math)
+  ConstantFPSDNode *N1C = isConstOrConstSplatFP(N1);
+  if (N1C && N1C->isZero())
+    if (N1C->isNegative() || Options.UnsafeFPMath || Flags.hasNoSignedZeros())
+      return N0;
+
   if (SDValue NewSel = foldBinOpIntoSelect(N))
     return NewSel;
 
@@ -10770,15 +10776,6 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
     return DAG.getNode(ISD::FSUB, DL, VT, N1IsFMul ? N0 : N1, Add, Flags);
   }
 
-  ConstantFPSDNode *N1C = isConstOrConstSplatFP(N1);
-  if (N1C && N1C->isZero()) {
-    if (N1C->isNegative() || Options.UnsafeFPMath ||
-        Flags.hasNoSignedZeros()) {
-      // fold (fadd A, 0) -> A
-      return N0;
-    }
-  }
-
   // No FP constant should be created after legalization as Instruction
   // Selection pass has a hard time dealing with FP constants.
   bool AllowNewConst = (Level < AfterLegalizeDAG);