[DAGCombine] require UnsafeFPMath for re-association of addition

Summary:
The affected transforms all implicitly use associativity of addition,
for which we usually require unsafe math to be enabled.

The "Aggressive" flag is only meant to convey information about the
performance of the fused ops relative to a fmul+fadd sequence.

Fixes Bug 31626.

Reviewers: spatel, hfinkel, mehdi_amini, arsenm, tstellarAMD

Subscribers: jholewinski, nemanjai, wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D28675

llvm-svn: 293635

1 files changed, 18 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 33863ca16f9..58942469556 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8405,9 +8405,12 @@ SDValue DAGCombiner::visitFADDForFMACombine(SDNode *N) {
   }
 
   // More folding opportunities when target permits.
-  if ((AllowFusion || HasFMAD)  && Aggressive) {
+  if (Aggressive) {
     // fold (fadd (fma x, y, (fmul u, v)), z) -> (fma x, y (fma u, v, z))
-    if (N0.getOpcode() == PreferredFusedOpcode &&
+    // FIXME: The UnsafeAlgebra flag should be propagated to FMA/FMAD, but FMF
+    // are currently only supported on binary nodes.
+    if (Options.UnsafeFPMath &&
+        N0.getOpcode() == PreferredFusedOpcode &&
         N0.getOperand(2).getOpcode() == ISD::FMUL &&
         N0->hasOneUse() && N0.getOperand(2)->hasOneUse()) {
       return DAG.getNode(PreferredFusedOpcode, SL, VT,
@@ -8419,7 +8422,10 @@ SDValue DAGCombiner::visitFADDForFMACombine(SDNode *N) {
     }
 
     // fold (fadd x, (fma y, z, (fmul u, v)) -> (fma y, z (fma u, v, x))
-    if (N1->getOpcode() == PreferredFusedOpcode &&
+    // FIXME: The UnsafeAlgebra flag should be propagated to FMA/FMAD, but FMF
+    // are currently only supported on binary nodes.
+    if (Options.UnsafeFPMath &&
+        N1->getOpcode() == PreferredFusedOpcode &&
         N1.getOperand(2).getOpcode() == ISD::FMUL &&
         N1->hasOneUse() && N1.getOperand(2)->hasOneUse()) {
       return DAG.getNode(PreferredFusedOpcode, SL, VT,
@@ -8649,10 +8655,13 @@ SDValue DAGCombiner::visitFSUBForFMACombine(SDNode *N) {
   }
 
   // More folding opportunities when target permits.
-  if ((AllowFusion || HasFMAD) && Aggressive) {
+  if (Aggressive) {
     // fold (fsub (fma x, y, (fmul u, v)), z)
     //   -> (fma x, y (fma u, v, (fneg z)))
-    if (N0.getOpcode() == PreferredFusedOpcode &&
+    // FIXME: The UnsafeAlgebra flag should be propagated to FMA/FMAD, but FMF
+    // are currently only supported on binary nodes.
+    if (Options.UnsafeFPMath &&
+        N0.getOpcode() == PreferredFusedOpcode &&
         N0.getOperand(2).getOpcode() == ISD::FMUL &&
         N0->hasOneUse() && N0.getOperand(2)->hasOneUse()) {
       return DAG.getNode(PreferredFusedOpcode, SL, VT,
@@ -8666,7 +8675,10 @@ SDValue DAGCombiner::visitFSUBForFMACombine(SDNode *N) {
 
     // fold (fsub x, (fma y, z, (fmul u, v)))
     //   -> (fma (fneg y), z, (fma (fneg u), v, x))
-    if (N1.getOpcode() == PreferredFusedOpcode &&
+    // FIXME: The UnsafeAlgebra flag should be propagated to FMA/FMAD, but FMF
+    // are currently only supported on binary nodes.
+    if (Options.UnsafeFPMath &&
+        N1.getOpcode() == PreferredFusedOpcode &&
         N1.getOperand(2).getOpcode() == ISD::FMUL) {
       SDValue N20 = N1.getOperand(2).getOperand(0);
       SDValue N21 = N1.getOperand(2).getOperand(1);