[DAGCombiner] loosen constraints for fsub+fadd fold

isNegatibleForFree() should not matter here (as the test diffs show)
because it's always a win to replace an fsub+fadd with fneg. The
problem in D50195 persists because either (1) we are doing these
folds in the wrong order or (2) we're missing another fold for fadd.

llvm-svn: 339299

1 files changed, 7 insertions, 14 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 9690d2c205a..f78688787dd 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10940,20 +10940,13 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
     return DAG.getNode(ISD::FADD, DL, VT, N0,
                        GetNegatedExpression(N1, DAG, LegalOperations), Flags);
 
-  // If 'unsafe math' is enabled, fold lots of things.
-  if (Options.UnsafeFPMath) {
-    // (fsub x, (fadd x, y)) -> (fneg y)
-    // (fsub x, (fadd y, x)) -> (fneg y)
-    if (N1.getOpcode() == ISD::FADD) {
-      SDValue N10 = N1->getOperand(0);
-      SDValue N11 = N1->getOperand(1);
-
-      if (N10 == N0 && isNegatibleForFree(N11, LegalOperations, TLI, &Options))
-        return GetNegatedExpression(N11, DAG, LegalOperations);
-
-      if (N11 == N0 && isNegatibleForFree(N10, LegalOperations, TLI, &Options))
-        return GetNegatedExpression(N10, DAG, LegalOperations);
-    }
+  if (Options.UnsafeFPMath && N1.getOpcode() == ISD::FADD) {
+    // X - (X + Y) -> -Y
+    if (N0 == N1->getOperand(0))
+      return DAG.getNode(ISD::FNEG, DL, VT, N1->getOperand(1));
+    // X - (Y + X) -> -Y
+    if (N0 == N1->getOperand(1))
+      return DAG.getNode(ISD::FNEG, DL, VT, N1->getOperand(0));
   }
 
   // FSUB -> FMA combines: