AMDGPU: Fix not emitting nofpexcept on fdiv expansion

In this awkward case, we have to emit custom pseudo-constrained FP
wrappers. InstrEmitter concludes that since a mayRaiseFPException
instruction had a chain, it can't add nofpexcept.

Test deferred until mayRaiseFPException is really set on everything.

Author: arsenm

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -7907,9 +7907,10 @@ SDValue SITargetLowering::lowerFastUnsafeFDIV(SDValue Op,
 }
 
 static SDValue getFPBinOp(SelectionDAG &DAG, unsigned Opcode, const SDLoc &SL,
-                          EVT VT, SDValue A, SDValue B, SDValue GlueChain) {
+                          EVT VT, SDValue A, SDValue B, SDValue GlueChain,
+                          SDNodeFlags Flags) {
   if (GlueChain->getNumValues() <= 1) {
-    return DAG.getNode(Opcode, SL, VT, A, B);
+    return DAG.getNode(Opcode, SL, VT, A, B, Flags);
   }
 
   assert(GlueChain->getNumValues() == 3);
@@ -7922,15 +7923,16 @@ static SDValue getFPBinOp(SelectionDAG &DAG, unsigned Opcode, const SDLoc &SL,
     break;
   }
 
-  return DAG.getNode(Opcode, SL, VTList, GlueChain.getValue(1), A, B,
-                     GlueChain.getValue(2));
+  return DAG.getNode(Opcode, SL, VTList,
+                     {GlueChain.getValue(1), A, B, GlueChain.getValue(2)},
+                     Flags);
 }
 
 static SDValue getFPTernOp(SelectionDAG &DAG, unsigned Opcode, const SDLoc &SL,
                            EVT VT, SDValue A, SDValue B, SDValue C,
-                           SDValue GlueChain) {
+                           SDValue GlueChain, SDNodeFlags Flags) {
   if (GlueChain->getNumValues() <= 1) {
-    return DAG.getNode(Opcode, SL, VT, A, B, C);
+    return DAG.getNode(Opcode, SL, VT, {A, B, C}, Flags);
   }
 
   assert(GlueChain->getNumValues() == 3);
@@ -7943,8 +7945,9 @@ static SDValue getFPTernOp(SelectionDAG &DAG, unsigned Opcode, const SDLoc &SL,
     break;
   }
 
-  return DAG.getNode(Opcode, SL, VTList, GlueChain.getValue(1), A, B, C,
-                     GlueChain.getValue(2));
+  return DAG.getNode(Opcode, SL, VTList,
+                     {GlueChain.getValue(1), A, B, C, GlueChain.getValue(2)},
+                     Flags);
 }
 
 SDValue SITargetLowering::LowerFDIV16(SDValue Op, SelectionDAG &DAG) const {
@@ -8018,6 +8021,13 @@ SDValue SITargetLowering::LowerFDIV32(SDValue Op, SelectionDAG &DAG) const {
   if (SDValue FastLowered = lowerFastUnsafeFDIV(Op, DAG))
     return FastLowered;
 
+  // The selection matcher assumes anything with a chain selecting to a
+  // mayRaiseFPException machine instruction. Since we're introducing a chain
+  // here, we need to explicitly report nofpexcept for the regular fdiv
+  // lowering.
+  SDNodeFlags Flags = Op->getFlags();
+  Flags.setNoFPExcept(true);
+
   SDLoc SL(Op);
   SDValue LHS = Op.getOperand(0);
   SDValue RHS = Op.getOperand(1);
@@ -8027,15 +8037,15 @@ SDValue SITargetLowering::LowerFDIV32(SDValue Op, SelectionDAG &DAG) const {
   SDVTList ScaleVT = DAG.getVTList(MVT::f32, MVT::i1);
 
   SDValue DenominatorScaled = DAG.getNode(AMDGPUISD::DIV_SCALE, SL, ScaleVT,
-                                          RHS, RHS, LHS);
+                                          {RHS, RHS, LHS}, Flags);
   SDValue NumeratorScaled = DAG.getNode(AMDGPUISD::DIV_SCALE, SL, ScaleVT,
-                                        LHS, RHS, LHS);
+                                        {LHS, RHS, LHS}, Flags);
 
   // Denominator is scaled to not be denormal, so using rcp is ok.
   SDValue ApproxRcp = DAG.getNode(AMDGPUISD::RCP, SL, MVT::f32,
-                                  DenominatorScaled);
+                                  DenominatorScaled, Flags);
   SDValue NegDivScale0 = DAG.getNode(ISD::FNEG, SL, MVT::f32,
-                                     DenominatorScaled);
+                                     DenominatorScaled, Flags);
 
   const unsigned Denorm32Reg = AMDGPU::Hwreg::ID_MODE |
                                (4 << AMDGPU::Hwreg::OFFSET_SHIFT_) |
@@ -8045,6 +8055,10 @@ SDValue SITargetLowering::LowerFDIV32(SDValue Op, SelectionDAG &DAG) const {
   const bool HasFP32Denormals = hasFP32Denormals(DAG.getMachineFunction());
 
   if (!HasFP32Denormals) {
+    // Note we can't use the STRICT_FMA/STRICT_FMUL for the non-strict FDIV
+    // lowering. The chain dependence is insufficient, and we need glue. We do
+    // not need the glue variants in a strictfp function.
+
     SDVTList BindParamVTs = DAG.getVTList(MVT::Other, MVT::Glue);
 
     SDNode *EnableDenorm;
@@ -8072,21 +8086,22 @@ SDValue SITargetLowering::LowerFDIV32(SDValue Op, SelectionDAG &DAG) const {
   }
 
   SDValue Fma0 = getFPTernOp(DAG, ISD::FMA, SL, MVT::f32, NegDivScale0,
-                             ApproxRcp, One, NegDivScale0);
+                             ApproxRcp, One, NegDivScale0, Flags);
 
   SDValue Fma1 = getFPTernOp(DAG, ISD::FMA, SL, MVT::f32, Fma0, ApproxRcp,
-                             ApproxRcp, Fma0);
+                             ApproxRcp, Fma0, Flags);
 
   SDValue Mul = getFPBinOp(DAG, ISD::FMUL, SL, MVT::f32, NumeratorScaled,
-                           Fma1, Fma1);
+                           Fma1, Fma1, Flags);
 
   SDValue Fma2 = getFPTernOp(DAG, ISD::FMA, SL, MVT::f32, NegDivScale0, Mul,
-                             NumeratorScaled, Mul);
+                             NumeratorScaled, Mul, Flags);
 
-  SDValue Fma3 = getFPTernOp(DAG, ISD::FMA, SL, MVT::f32, Fma2, Fma1, Mul, Fma2);
+  SDValue Fma3 = getFPTernOp(DAG, ISD::FMA, SL, MVT::f32,
+                             Fma2, Fma1, Mul, Fma2, Flags);
 
   SDValue Fma4 = getFPTernOp(DAG, ISD::FMA, SL, MVT::f32, NegDivScale0, Fma3,
-                             NumeratorScaled, Fma3);
+                             NumeratorScaled, Fma3, Flags);
 
   if (!HasFP32Denormals) {
     SDNode *DisableDenorm;
@@ -8113,9 +8128,9 @@ SDValue SITargetLowering::LowerFDIV32(SDValue Op, SelectionDAG &DAG) const {
 
   SDValue Scale = NumeratorScaled.getValue(1);
   SDValue Fmas = DAG.getNode(AMDGPUISD::DIV_FMAS, SL, MVT::f32,
-                             Fma4, Fma1, Fma3, Scale);
+                             {Fma4, Fma1, Fma3, Scale}, Flags);
 
-  return DAG.getNode(AMDGPUISD::DIV_FIXUP, SL, MVT::f32, Fmas, RHS, LHS);
+  return DAG.getNode(AMDGPUISD::DIV_FIXUP, SL, MVT::f32, Fmas, RHS, LHS, Flags);
 }
 
 SDValue SITargetLowering::LowerFDIV64(SDValue Op, SelectionDAG &DAG) const {