Use the 'arcp' fast-math-flag when combining repeated FP divisors

This is a usage of the IR-level fast-math-flags now that they are propagated to SDNodes. 
This was originally part of D8900.

Removing the global 'enable-unsafe-fp-math' checks will require auto-upgrade and 
possibly other changes.

Differential Revision: http://reviews.llvm.org/D9708

llvm-svn: 251450

1 files changed, 11 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 957aa7bf90b..31f0df99d47 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8477,7 +8477,9 @@ SDValue DAGCombiner::visitFMA(SDNode *N) {
 // FDIVs may be lower than the cost of one FDIV and two FMULs. Another reason
 // is the critical path is increased from "one FDIV" to "one FDIV + one FMUL".
 SDValue DAGCombiner::combineRepeatedFPDivisors(SDNode *N) {
-  if (!DAG.getTarget().Options.UnsafeFPMath)
+  bool UnsafeMath = DAG.getTarget().Options.UnsafeFPMath;
+  const SDNodeFlags *Flags = N->getFlags();
+  if (!UnsafeMath && !Flags->hasAllowReciprocal())
     return SDValue();
 
   // Skip if current node is a reciprocal.
@@ -8496,9 +8498,14 @@ SDValue DAGCombiner::combineRepeatedFPDivisors(SDNode *N) {
   // Find all FDIV users of the same divisor.
   // Use a set because duplicates may be present in the user list.
   SetVector<SDNode *> Users;
-  for (auto *U : N1->uses())
-    if (U->getOpcode() == ISD::FDIV && U->getOperand(1) == N1)
-      Users.insert(U);
+  for (auto *U : N1->uses()) {
+    if (U->getOpcode() == ISD::FDIV && U->getOperand(1) == N1) {
+      // This division is eligible for optimization only if global unsafe math
+      // is enabled or if this division allows reciprocal formation.
+      if (UnsafeMath || U->getFlags()->hasAllowReciprocal())
+        Users.insert(U);
+    }
+  }
 
   // Now that we have the actual number of divisor uses, make sure it meets
   // the minimum threshold specified by the target.
@@ -8508,7 +8515,6 @@ SDValue DAGCombiner::combineRepeatedFPDivisors(SDNode *N) {
   EVT VT = N->getValueType(0);
   SDLoc DL(N);
   SDValue FPOne = DAG.getConstantFP(1.0, DL, VT);
-  const SDNodeFlags *Flags = &cast<BinaryWithFlagsSDNode>(N)->Flags;
   SDValue Reciprocal = DAG.getNode(ISD::FDIV, DL, VT, FPOne, N1, Flags);
 
   // Dividend / Divisor -> Dividend * Reciprocal