Utilize new SDNode flag functionality to expand current support for fsub

Summary: This patch originated from D46562 and is a proper subset, with some issues addressed for fsub.

Reviewers: spatel, hfinkel, wristow, arsenm

Reviewed By: spatel

Subscribers: wdng

Differential Revision: https://reviews.llvm.org/D47910

llvm-svn: 334306

1 files changed, 23 insertions, 17 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 64b0ee571a2..8b7abdb0395 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -673,6 +673,7 @@ static char isNegatibleForFree(SDValue Op, bool LegalOperations,
 
   // Don't allow anything with multiple uses unless we know it is free.
   EVT VT = Op.getValueType();
+  const SDNodeFlags Flags = Op->getFlags();
   if (!Op.hasOneUse())
     if (!(Op.getOpcode() == ISD::FP_EXTEND &&
           TLI.isFPExtFree(VT, Op.getOperand(0).getValueType())))
@@ -710,7 +711,7 @@ static char isNegatibleForFree(SDValue Op, bool LegalOperations,
   case ISD::FSUB:
     // We can't turn -(A-B) into B-A when we honor signed zeros.
     if (!Options->NoSignedZerosFPMath &&
-        !Op.getNode()->getFlags().hasNoSignedZeros())
+        !Flags.hasNoSignedZeros())
       return 0;
 
     // fold (fneg (fsub A, B)) -> (fsub B, A)
@@ -10414,15 +10415,23 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
   if (SDValue NewSel = foldBinOpIntoSelect(N))
     return NewSel;
 
-  // fold (fsub A, (fneg B)) -> (fadd A, B)
-  if (isNegatibleForFree(N1, LegalOperations, TLI, &Options))
-    return DAG.getNode(ISD::FADD, DL, VT, N0,
-                       GetNegatedExpression(N1, DAG, LegalOperations), Flags);
+  // (fsub A, 0) -> A
+  if (N1CFP && N1CFP->isZero()) {
+    if (!N1CFP->isNegative() || Options.UnsafeFPMath ||
+        Flags.hasNoSignedZeros()) {
+      return N0;
+    }
+  }
 
-  // FIXME: Auto-upgrade the target/function-level option.
-  if (Options.NoSignedZerosFPMath  || N->getFlags().hasNoSignedZeros()) {
-    // (fsub 0, B) -> -B
-    if (N0CFP && N0CFP->isZero()) {
+  if (N0 == N1) {
+    // (fsub x, x) -> 0.0
+    if (Options.UnsafeFPMath || Flags.hasNoNaNs())
+      return DAG.getConstantFP(0.0f, DL, VT);
+  }
+
+  // (fsub 0, B) -> -B
+  if (N0CFP && N0CFP->isZero()) {
+    if (Options.NoSignedZerosFPMath || Flags.hasNoSignedZeros()) {
       if (isNegatibleForFree(N1, LegalOperations, TLI, &Options))
         return GetNegatedExpression(N1, DAG, LegalOperations);
       if (!LegalOperations || TLI.isOperationLegal(ISD::FNEG, VT))
@@ -10430,16 +10439,13 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
     }
   }
 
+  // fold (fsub A, (fneg B)) -> (fadd A, B)
+  if (isNegatibleForFree(N1, LegalOperations, TLI, &Options))
+    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 A, 0) -> A
-    if (N1CFP && N1CFP->isZero())
-      return N0;
-
-    // (fsub x, x) -> 0.0
-    if (N0 == N1)
-      return DAG.getConstantFP(0.0f, DL, VT);
-
     // (fsub x, (fadd x, y)) -> (fneg y)
     // (fsub x, (fadd y, x)) -> (fneg y)
     if (N1.getOpcode() == ISD::FADD) {