Utilize new SDNode flag functionality to expand current support for fadd

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

Reviewers: spatel, hfinkel, wristow, arsenm, javed.absar

Reviewed By: spatel

Subscribers: wdng, nhaehnle

Differential Revision: https://reviews.llvm.org/D47909

llvm-svn: 334996

2 files changed, 15 insertions, 29 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b66b2f8730a..b3f5531e987 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10327,20 +10327,21 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
     return DAG.getNode(ISD::FSUB, DL, VT, N1IsFMul ? N0 : N1, Add, Flags);
   }
 
-  // FIXME: Auto-upgrade the target/function-level option.
-  if (Options.NoSignedZerosFPMath || N->getFlags().hasNoSignedZeros()) {
-    // fold (fadd A, 0) -> A
-    if (ConstantFPSDNode *N1C = isConstOrConstSplatFP(N1))
-      if (N1C->isZero())
-        return N0;
+  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);
 
-  // TODO: fmf test for NaNs could be done here too
-  if (Options.UnsafeFPMath && AllowNewConst) {
+  // If 'unsafe math' or nnan is enabled, fold lots of things.
+  if ((Options.UnsafeFPMath || Flags.hasNoNaNs()) && AllowNewConst) {
     // If allowed, fold (fadd (fneg x), x) -> 0.0
     if (N0.getOpcode() == ISD::FNEG && N0.getOperand(0) == N1)
       return DAG.getConstantFP(0.0, DL, VT);
@@ -10350,9 +10351,12 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
       return DAG.getConstantFP(0.0, DL, VT);
   }
 
-  // If 'unsafe math' is enabled, fold lots of things.
-  // TODO: fmf testing for reassoc/nsz could be done here too
-  if (Options.UnsafeFPMath && AllowNewConst) {
+  // If 'unsafe math' or reassoc and nsz, fold lots of things.
+  // TODO: break out portions of the transformations below for which Unsafe is
+  //       considered and which do not require both nsz and reassoc
+  if ((Options.UnsafeFPMath ||
+       (Flags.hasAllowReassociation() && Flags.hasNoSignedZeros())) &&
+      AllowNewConst) {
     // fadd (fadd x, c1), c2 -> fadd x, c1 + c2
     if (N1CFP && N0.getOpcode() == ISD::FADD &&
         isConstantFPBuildVectorOrConstantFP(N0.getOperand(1))) {
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index d227c4a0efa..4fdd3de0ebc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -4442,24 +4442,6 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
   case ISD::FMUL:
   case ISD::FDIV:
   case ISD::FREM:
-    if (getTarget().Options.UnsafeFPMath) {
-      if (Opcode == ISD::FADD) {
-        // x+0 --> x
-        if (N2CFP && N2CFP->getValueAPF().isZero())
-          return N1;
-      } else if (Opcode == ISD::FSUB) {
-        // x-0 --> x
-        if (N2CFP && N2CFP->getValueAPF().isZero())
-          return N1;
-      } else if (Opcode == ISD::FMUL) {
-        // x*0 --> 0
-        if (N2CFP && N2CFP->isZero())
-          return N2;
-        // x*1 --> x
-        if (N2CFP && N2CFP->isExactlyValue(1.0))
-          return N1;
-      }
-    }
     assert(VT.isFloatingPoint() && "This operator only applies to FP types!");
     assert(N1.getValueType() == N2.getValueType() &&
            N1.getValueType() == VT && "Binary operator types must match!");