propagate fast-math-flags on DAG nodes

After D10403, we had FMF in the DAG but disabled by default. Nick reported no crashing errors after some stress testing, 
so I enabled them at r243687. However, Escha soon notified us of a bug not covered by any in-tree regression tests: 
if we don't propagate the flags, we may fail to CSE DAG nodes because differing FMF causes them to not match. There is
one test case in this patch to prove that point.

This patch hopes to fix or leave a 'TODO' for all of the in-tree places where we create nodes that are FMF-capable. I 
did this by putting an assert in SelectionDAG.getNode() to find any FMF-capable node that was being created without FMF
( D11807 ). I then ran all regression tests and test-suite and confirmed that everything passes.

This patch exposes remaining work to get DAG FMF to be fully functional: (1) add the flags to non-binary nodes such as
FCMP, FMA and FNEG; (2) add the flags to intrinsics; (3) use the flags as conditions for transforms rather than the
current global settings.

Differential Revision: http://reviews.llvm.org/D12095

llvm-svn: 247815

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index ef42a2972bf..d0830a9e583 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -1000,6 +1000,8 @@ SDValue SITargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
   SDLoc DL(Op);
   unsigned IntrinsicID = cast<ConstantSDNode>(Op.getOperand(0))->getZExtValue();
 
+  // TODO: Should this propagate fast-math-flags?
+
   switch (IntrinsicID) {
   case Intrinsic::r600_read_ngroups_x:
     return LowerParameter(DAG, VT, VT, DL, DAG.getEntryNode(),
@@ -1248,8 +1250,10 @@ SDValue SITargetLowering::LowerFastFDIV(SDValue Op, SelectionDAG &DAG) const {
   if (Unsafe) {
     // Turn into multiply by the reciprocal.
     // x / y -> x * (1.0 / y)
+    SDNodeFlags Flags;
+    Flags.setUnsafeAlgebra(true);
     SDValue Recip = DAG.getNode(AMDGPUISD::RCP, SL, VT, RHS);
-    return DAG.getNode(ISD::FMUL, SL, VT, LHS, Recip);
+    return DAG.getNode(ISD::FMUL, SL, VT, LHS, Recip, &Flags);
   }
 
   return SDValue();
@@ -1286,6 +1290,8 @@ SDValue SITargetLowering::LowerFDIV32(SDValue Op, SelectionDAG &DAG) const {
 
   SDValue r3 = DAG.getNode(ISD::SELECT, SL, MVT::f32, r2, K1, One);
 
+  // TODO: Should this propagate fast-math-flags?
+
   r1 = DAG.getNode(ISD::FMUL, SL, MVT::f32, RHS, r3);
 
   SDValue r0 = DAG.getNode(AMDGPUISD::RCP, SL, MVT::f32, r1);
@@ -1405,6 +1411,7 @@ SDValue SITargetLowering::LowerTrig(SDValue Op, SelectionDAG &DAG) const {
   SDLoc DL(Op);
   EVT VT = Op.getValueType();
   SDValue Arg = Op.getOperand(0);
+  // TODO: Should this propagate fast-math-flags?
   SDValue FractPart = DAG.getNode(AMDGPUISD::FRACT, DL, VT,
                                   DAG.getNode(ISD::FMUL, DL, VT, Arg,
                                               DAG.getConstantFP(0.5/M_PI, DL,