DAG: Fold fma (fneg x), K, y -> fma x, -K, y

[RKSimon]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

10128

Do we need a OneUse test on FNEG(N0)?

[arsenm]

Fix PPC test failures

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

10128

I don't think so because this eliminates a use of fneg.

[RKSimon]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

10128

Do we need a OneUse test on FNEG(N0)?

I don't think so because this eliminates a use of fneg.

OK - what about permitting negations of FpImmLegal constants if the negated value is FpImmLegal too?

[arsenm]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

10128

As far as I can tell no target does anything that would allow the negated value to become legal, so it doesn't seem worth the effort

[RKSimon]

LGTM

[arsenm]

r316753

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if (N1CFP) {
 
     if (N1CFP->isExactlyValue(-1.0) &&
         (!LegalOperations || TLI.isOperationLegal(ISD::FNEG, VT))) {
       SDValue RHSNeg = DAG.getNode(ISD::FNEG, DL, VT, N0);
       AddToWorklist(RHSNeg.getNode());
       // TODO: The FMA node should have flags that propagate to this node.
       return DAG.getNode(ISD::FADD, DL, VT, N2, RHSNeg);
     }
+
+    // fma (fneg x), K, y -> fma x -K, y
+    if (N0.getOpcode() == ISD::FNEG &&
+        (TLI.isOperationLegal(ISD::ConstantFP, VT) ||
+         (N1.hasOneUse() && !TLI.isFPImmLegal(N1CFP->getValueAPF(), VT)))) {
+      return DAG.getNode(ISD::FMA, DL, VT, N0.getOperand(0),
+                         DAG.getNode(ISD::FNEG, DL, VT, N1, Flags), N2);
+    }
   }
 
   if (Options.UnsafeFPMath) {
     // (fma x, c, x) -> (fmul x, (c+1))
     if (N1CFP && N0 == N2) {
       return DAG.getNode(ISD::FMUL, DL, VT, N0,
                          DAG.getNode(ISD::FADD, DL, VT, N1,
                                      DAG.getConstantFP(1.0, DL, VT), Flags),

test/CodeGen/AMDGPU/fma-combine.ll

define amdgpu_kernel void @test_f64_interp(double addrspace(1)* %out,
   %t1 = fsub double 1.0, %t
   %tx = fmul double %x, %t
   %ty = fmul double %y, %t1
   %r = fadd double %tx, %ty
   store double %r, double addrspace(1)* %out
   ret void
 }
 
+; Make sure negative constant cancels out fneg
+; GCN-LABEL: {{^}}fma_neg_2.0_neg_a_b_f32:
+; GCN: {{buffer|flat|global}}_load_dword [[A:v[0-9]+]]
+; GCN: {{buffer|flat|global}}_load_dword [[B:v[0-9]+]]
+; GCN-NOT: [[A]]
+; GCN-NOT: [[B]]
+; GCN: v_fma_f32 v{{[0-9]+}}, [[A]], 2.0, [[B]]
+define amdgpu_kernel void @fma_neg_2.0_neg_a_b_f32(float addrspace(1)* %out, float addrspace(1)* %in) #0 {
+  %tid = call i32 @llvm.amdgcn.workitem.id.x()
+  %gep.0 = getelementptr float, float addrspace(1)* %out, i32 %tid
+  %gep.1 = getelementptr float, float addrspace(1)* %gep.0, i32 1
+  %gep.out = getelementptr float, float addrspace(1)* %out, i32 %tid
+
+  %r1 = load volatile float, float addrspace(1)* %gep.0
+  %r2 = load volatile float, float addrspace(1)* %gep.1
+
+  %r1.fneg = fsub float -0.000000e+00, %r1
+
+  %r3 = tail call float @llvm.fma.f32(float -2.0, float %r1.fneg, float %r2)
+  store float %r3, float addrspace(1)* %gep.out
+  ret void
+}
+
+; GCN-LABEL: {{^}}fma_2.0_neg_a_b_f32:
+; GCN: {{buffer|flat|global}}_load_dword [[A:v[0-9]+]]
+; GCN: {{buffer|flat|global}}_load_dword [[B:v[0-9]+]]
+; GCN-NOT: [[A]]
+; GCN-NOT: [[B]]
+; GCN: v_fma_f32 v{{[0-9]+}}, [[A]], -2.0, [[B]]
+define amdgpu_kernel void @fma_2.0_neg_a_b_f32(float addrspace(1)* %out, float addrspace(1)* %in) #0 {
+  %tid = call i32 @llvm.amdgcn.workitem.id.x()
+  %gep.0 = getelementptr float, float addrspace(1)* %out, i32 %tid
+  %gep.1 = getelementptr float, float addrspace(1)* %gep.0, i32 1
+  %gep.out = getelementptr float, float addrspace(1)* %out, i32 %tid
+
+  %r1 = load volatile float, float addrspace(1)* %gep.0
+  %r2 = load volatile float, float addrspace(1)* %gep.1
+
+  %r1.fneg = fsub float -0.000000e+00, %r1
+
+  %r3 = tail call float @llvm.fma.f32(float 2.0, float %r1.fneg, float %r2)
+  store float %r3, float addrspace(1)* %gep.out
+  ret void
+}
+
 attributes #0 = { nounwind readnone }
 attributes #1 = { nounwind }
+

test/CodeGen/AMDGPU/fmuladd.f16.ll

 }
 
 ; GCN-LABEL: {{^}}fmuladd_neg_2.0_neg_a_b_f16
 ; GCN: {{buffer|flat}}_load_ushort [[R1:v[0-9]+]],
 ; GCN: {{buffer|flat}}_load_ushort [[R2:v[0-9]+]],
 ; VI-FLUSH: v_mac_f16_e32 [[R2]], 2.0, [[R1]]
 ; VI-FLUSH: flat_store_short v{{\[[0-9]+:[0-9]+\]}}, [[R2]]
 
-; VI-DENORM: v_fma_f16 [[RESULT:v[0-9]+]], -[[R1]], -2.0, [[R2]]
+; VI-DENORM: v_fma_f16 [[RESULT:v[0-9]+]], [[R1]], 2.0, [[R2]]
 ; VI-DENORM: flat_store_short v{{\[[0-9]+:[0-9]+\]}}, [[RESULT]]
 define amdgpu_kernel void @fmuladd_neg_2.0_neg_a_b_f16(half addrspace(1)* %out, half addrspace(1)* %in) #0 {
   %tid = call i32 @llvm.amdgcn.workitem.id.x()
   %gep.0 = getelementptr half, half addrspace(1)* %out, i32 %tid
   %gep.1 = getelementptr half, half addrspace(1)* %gep.0, i32 1
   %gep.out = getelementptr half, half addrspace(1)* %out, i32 %tid
 
   %r1 = load volatile half, half addrspace(1)* %gep.0
   %r2 = load volatile half, half addrspace(1)* %gep.1
 
   %r1.fneg = fsub half -0.000000e+00, %r1
 
   %r3 = tail call half @llvm.fmuladd.f16(half -2.0, half %r1.fneg, half %r2)
   store half %r3, half addrspace(1)* %gep.out
   ret void
 }
 
 ; GCN-LABEL: {{^}}fmuladd_2.0_neg_a_b_f16
 ; GCN: {{buffer|flat}}_load_ushort [[R1:v[0-9]+]],
 ; GCN: {{buffer|flat}}_load_ushort [[R2:v[0-9]+]],
 ; VI-FLUSH: v_mac_f16_e32 [[R2]], -2.0, [[R1]]
 ; VI-FLUSH: flat_store_short v{{\[[0-9]+:[0-9]+\]}}, [[R2]]
 
-; VI-DENORM: v_fma_f16 [[RESULT:v[0-9]+]], -[[R1]], 2.0, [[R2]]
+; VI-DENORM: v_fma_f16 [[RESULT:v[0-9]+]], [[R1]], -2.0, [[R2]]
 ; VI-DENORM: flat_store_short v{{\[[0-9]+:[0-9]+\]}}, [[RESULT]]
 define amdgpu_kernel void @fmuladd_2.0_neg_a_b_f16(half addrspace(1)* %out, half addrspace(1)* %in) #0 {
   %tid = call i32 @llvm.amdgcn.workitem.id.x()
   %gep.0 = getelementptr half, half addrspace(1)* %out, i32 %tid
   %gep.1 = getelementptr half, half addrspace(1)* %gep.0, i32 1
   %gep.out = getelementptr half, half addrspace(1)* %out, i32 %tid
 
   %r1 = load volatile half, half addrspace(1)* %gep.0

test/CodeGen/AMDGPU/fmuladd.f32.ll

 ; GCN-LABEL: {{^}}fmuladd_neg_2.0_neg_a_b_f32
 ; GCN: {{buffer|flat}}_load_dword [[R1:v[0-9]+]],
 ; GCN: {{buffer|flat}}_load_dword [[R2:v[0-9]+]],
 
 ; GCN-FLUSH: v_mac_f32_e32 [[R2]], 2.0, [[R1]]
 ; SI-FLUSH: buffer_store_dword [[R2]]
 ; VI-FLUSH: flat_store_dword v{{\[[0-9]+:[0-9]+\]}}, [[R2]]
 
-; GCN-DENORM-FASTFMA: v_fma_f32 [[RESULT:v[0-9]+]], -[[R1]], -2.0, [[R2]]
+; GCN-DENORM-FASTFMA: v_fma_f32 [[RESULT:v[0-9]+]], [[R1]], 2.0, [[R2]]
 
 ; GCN-DENORM-SLOWFMA: v_add_f32_e32 [[TMP:v[0-9]+]], [[R1]], [[R1]]
 ; GCN-DENORM-SLOWFMA: v_add_f32_e32 [[RESULT:v[0-9]+]], [[R2]], [[TMP]]
 
 ; SI-DENORM: buffer_store_dword [[RESULT]]
 ; VI-DENORM: flat_store_dword v{{\[[0-9]+:[0-9]+\]}}, [[RESULT]]
 define amdgpu_kernel void @fmuladd_neg_2.0_neg_a_b_f32(float addrspace(1)* %out, float addrspace(1)* %in) #0 {
   %tid = call i32 @llvm.amdgcn.workitem.id.x()

 ; GCN-LABEL: {{^}}fmuladd_2.0_neg_a_b_f32:
 ; GCN: {{buffer|flat}}_load_dword [[R1:v[0-9]+]],
 ; GCN: {{buffer|flat}}_load_dword [[R2:v[0-9]+]],
 
 ; GCN-FLUSH: v_mac_f32_e32 [[R2]], -2.0, [[R1]]
 ; SI-FLUSH: buffer_store_dword [[R2]]
 ; VI-FLUSH: flat_store_dword v{{\[[0-9]+:[0-9]+\]}}, [[R2]]
 
-; GCN-DENORM-FASTFMA: v_fma_f32 [[RESULT:v[0-9]+]], -[[R1]], 2.0, [[R2]]
+; GCN-DENORM-FASTFMA: v_fma_f32 [[RESULT:v[0-9]+]], [[R1]], -2.0, [[R2]]
 
 ; GCN-DENORM-SLOWFMA: v_add_f32_e32 [[TMP:v[0-9]+]], [[R1]], [[R1]]
 ; GCN-DENORM-SLOWFMA: v_sub_f32_e32 [[RESULT:v[0-9]+]], [[R2]], [[TMP]]
 
 ; SI-DENORM: buffer_store_dword [[RESULT]]
 ; VI-DENORM: flat_store_dword v{{\[[0-9]+:[0-9]+\]}}, [[RESULT]]
 define amdgpu_kernel void @fmuladd_2.0_neg_a_b_f32(float addrspace(1)* %out, float addrspace(1)* %in) #0 {
   %tid = call i32 @llvm.amdgcn.workitem.id.x()