[PATCH] D155443: AMDGPU: Preserve flags in fdiv_fast lowering

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
arsenm added reviewers: AMDGPU, foad, Pierre-vh, rampitec.
Herald added subscribers: StephenFan, kerbowa, hiraditya, tpr, dstuttard, yaxunl, jvesely, kzhuravl.
Herald added a project: All.
arsenm requested review of this revision.
Herald added a subscriber: wdng.
Herald added a project: LLVM.

We were dropping the flags and thus blocking contract into potential
fadd users. GlobalISel was already preserving the flags here.


https://reviews.llvm.org/D155443

Files:
  llvm/lib/Target/AMDGPU/SIISelLowering.cpp
  llvm/test/CodeGen/AMDGPU/fdiv.ll


Index: llvm/test/CodeGen/AMDGPU/fdiv.ll
===================================================================
--- llvm/test/CodeGen/AMDGPU/fdiv.ll
+++ llvm/test/CodeGen/AMDGPU/fdiv.ll
@@ -3828,8 +3828,7 @@
 ; GFX11-NEXT:    v_rcp_f32_e32 v1, v1
 ; GFX11-NEXT:    s_waitcnt_depctr 0xfff
 ; GFX11-NEXT:    v_mul_f32_e32 v0, v0, v1
-; GFX11-NEXT:    v_mul_f32_e32 v0, v3, v0
-; GFX11-NEXT:    v_add_f32_e32 v0, v0, v2
+; GFX11-NEXT:    v_fma_f32 v0, v3, v0, v2
 ; GFX11-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; EG-LABEL: v_fdiv_f32_daz_25ulp_contractable_user:
@@ -5087,8 +5086,7 @@
 ; GFX11-NEXT:    v_rcp_f32_e32 v1, v1
 ; GFX11-NEXT:    s_waitcnt_depctr 0xfff
 ; GFX11-NEXT:    v_mul_f32_e32 v0, v0, v1
-; GFX11-NEXT:    v_mul_f32_e32 v0, v3, v0
-; GFX11-NEXT:    v_add_f32_e32 v0, v0, v2
+; GFX11-NEXT:    v_fma_f32 v0, v3, v0, v2
 ; GFX11-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; EG-LABEL: v_fdiv_f32_daz_25ulp__nnan_ninf_contractable_user:
Index: llvm/lib/Target/AMDGPU/SIISelLowering.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -9271,11 +9271,12 @@
 
 // Faster 2.5 ULP division that does not support denormals.
 SDValue SITargetLowering::lowerFDIV_FAST(SDValue Op, SelectionDAG &DAG) const {
+  SDNodeFlags Flags = Op->getFlags();
   SDLoc SL(Op);
   SDValue LHS = Op.getOperand(1);
   SDValue RHS = Op.getOperand(2);
 
-  SDValue r1 = DAG.getNode(ISD::FABS, SL, MVT::f32, RHS);
+  SDValue r1 = DAG.getNode(ISD::FABS, SL, MVT::f32, RHS, Flags);
 
   const APFloat K0Val(0x1p+96f);
   const SDValue K0 = DAG.getConstantFP(K0Val, SL, MVT::f32);
@@ -9290,17 +9291,16 @@
 
   SDValue r2 = DAG.getSetCC(SL, SetCCVT, r1, K0, ISD::SETOGT);
 
-  SDValue r3 = DAG.getNode(ISD::SELECT, SL, MVT::f32, r2, K1, One);
+  SDValue r3 = DAG.getNode(ISD::SELECT, SL, MVT::f32, r2, K1, One, Flags);
 
-  // TODO: Should this propagate fast-math-flags?
-  r1 = DAG.getNode(ISD::FMUL, SL, MVT::f32, RHS, r3);
+  r1 = DAG.getNode(ISD::FMUL, SL, MVT::f32, RHS, r3, Flags);
 
   // rcp does not support denormals.
-  SDValue r0 = DAG.getNode(AMDGPUISD::RCP, SL, MVT::f32, r1);
+  SDValue r0 = DAG.getNode(AMDGPUISD::RCP, SL, MVT::f32, r1, Flags);
 
-  SDValue Mul = DAG.getNode(ISD::FMUL, SL, MVT::f32, LHS, r0);
+  SDValue Mul = DAG.getNode(ISD::FMUL, SL, MVT::f32, LHS, r0, Flags);
 
-  return DAG.getNode(ISD::FMUL, SL, MVT::f32, r3, Mul);
+  return DAG.getNode(ISD::FMUL, SL, MVT::f32, r3, Mul, Flags);
 }
 
 // Returns immediate value for setting the F32 denorm mode when using the


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