[DAGCombiner] Remove NoSignedZerosFPMath uses in visitFSUB (#160974)

Remove NoSignedZerosFPMath in visitFSUB part, we should always use
instruction level fast math flags.

Author: paperchalice

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -17983,8 +17983,7 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
 
   // (fsub A, 0) -> A
   if (N1CFP && N1CFP->isZero()) {
-    if (!N1CFP->isNegative() || Options.NoSignedZerosFPMath ||
-        Flags.hasNoSignedZeros()) {
+    if (!N1CFP->isNegative() || Flags.hasNoSignedZeros()) {
       return N0;
     }
   }
@@ -17997,8 +17996,7 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
 
   // (fsub -0.0, N1) -> -N1
   if (N0CFP && N0CFP->isZero()) {
-    if (N0CFP->isNegative() ||
-        (Options.NoSignedZerosFPMath || Flags.hasNoSignedZeros())) {
+    if (N0CFP->isNegative() || Flags.hasNoSignedZeros()) {
       // We cannot replace an FSUB(+-0.0,X) with FNEG(X) when denormals are
       // flushed to zero, unless all users treat denorms as zero (DAZ).
       // FIXME: This transform will change the sign of a NaN and the behavior
@@ -18014,8 +18012,7 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
     }
   }
 
-  if ((Options.NoSignedZerosFPMath ||
-       (Flags.hasAllowReassociation() && Flags.hasNoSignedZeros())) &&
+  if (Flags.hasAllowReassociation() && Flags.hasNoSignedZeros() &&
       N1.getOpcode() == ISD::FADD) {
     // X - (X + Y) -> -Y
     if (N0 == N1->getOperand(0))

llvm/test/CodeGen/AMDGPU/fneg-combines.ll

@@ -5015,7 +5015,7 @@ define amdgpu_kernel void @v_fneg_fp_round_fneg_f64_to_f32(ptr addrspace(1) %out
   %a.gep = getelementptr inbounds double, ptr addrspace(1) %a.ptr, i64 %tid.ext
   %out.gep = getelementptr inbounds float, ptr addrspace(1) %out, i64 %tid.ext
   %a = load volatile double, ptr addrspace(1) %a.gep
-  %fneg.a = fsub double -0.000000e+00, %a
+  %fneg.a = fsub nsz double -0.000000e+00, %a
   %fpround = fptrunc double %fneg.a to float
   %fneg = fneg float %fpround
   store float %fneg, ptr addrspace(1) %out.gep

llvm/test/CodeGen/AMDGPU/fneg-combines.new.ll

@@ -4441,25 +4441,40 @@ define float @v_fneg_fabs_select_infloop_regression(float %arg, i1 %arg1) {
   ret float %i3
 }
 
-define float @v_fmul_0_fsub_0_infloop_regression(float %arg) {
-; GCN-SAFE-LABEL: v_fmul_0_fsub_0_infloop_regression:
+define float @v_fmul_0_fsub_0_safe_infloop_regression(float %arg) {
+; GCN-SAFE-LABEL: v_fmul_0_fsub_0_safe_infloop_regression:
 ; GCN-SAFE:       ; %bb.0: ; %bb
 ; GCN-SAFE-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GCN-SAFE-NEXT:    v_mul_f32_e32 v0, 0, v0
 ; GCN-SAFE-NEXT:    v_sub_f32_e32 v0, 0, v0
 ; GCN-SAFE-NEXT:    s_setpc_b64 s[30:31]
 ;
-; GCN-NSZ-LABEL: v_fmul_0_fsub_0_infloop_regression:
-; GCN-NSZ:       ; %bb.0: ; %bb
-; GCN-NSZ-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; GCN-NSZ-NEXT:    v_mul_f32_e32 v0, 0x80000000, v0
-; GCN-NSZ-NEXT:    s_setpc_b64 s[30:31]
+; SI-NSZ-LABEL: v_fmul_0_fsub_0_safe_infloop_regression:
+; SI-NSZ:       ; %bb.0: ; %bb
+; SI-NSZ-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; SI-NSZ-NEXT:    s_brev_b32 s4, 1
+; SI-NSZ-NEXT:    v_fma_f32 v0, v0, s4, 0
+; SI-NSZ-NEXT:    s_setpc_b64 s[30:31]
+; FIXME: utils/update_llc_test_checks.py will generate redundant VI
+; labels, remove them, they will cause test failure.
 bb:
   %i = fmul float %arg, 0.0
   %i1 = fsub float 0.0, %i
   ret float %i1
 }
 
+define float @v_fmul_0_fsub_0_nsz_infloop_regression(float %arg) {
+; GCN-LABEL: v_fmul_0_fsub_0_nsz_infloop_regression:
+; GCN:       ; %bb.0: ; %bb
+; GCN-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; GCN-NEXT:    v_mul_f32_e32 v0, 0x80000000, v0
+; GCN-NEXT:    s_setpc_b64 s[30:31]
+bb:
+  %i = fmul float %arg, 0.0
+  %i1 = fsub nsz float 0.0, %i
+  ret float %i1
+}
+
 declare i32 @llvm.amdgcn.workitem.id.x() #1
 declare float @llvm.fma.f32(float, float, float) #1
 declare <2 x float> @llvm.fma.v2f32(<2 x float>, <2 x float>, <2 x float>)

llvm/test/CodeGen/X86/vec_unsafe-fp-math.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc < %s -enable-unsafe-fp-math -enable-no-signed-zeros-fp-math -mtriple=x86_64-unknown-unknown | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s
 
 ; Make sure that vectors get the same benefits as scalars when using unsafe-fp-math.
 
@@ -18,7 +18,7 @@ define <4 x float> @vec_fneg(<4 x float> %x) {
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    xorps {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0
 ; CHECK-NEXT:    retq
-  %sub = fsub <4 x float> zeroinitializer, %x
+  %sub = fsub nsz <4 x float> zeroinitializer, %x
   ret <4 x float> %sub
 }