[AMDGPU][GlobalISel] Transform (fsub (fpext (fmul x, y)), z) -> (fma (fpext x), (fpext y), (fneg z))

[matejam]

Summary

Instead of sub and mul instructions, use v_mad, v_mac or v_fma if fma
instructions are faster and are legal for the given architecture.
Combiner for a case that has one multiplication, which gets extended, and
from that the third argument is subtracted. This combiner will transform
that into two extends and one negation within the fma/fmad instruction.

[matejam]

Put back the accidentally deleted combiner from the list of combiners (load_or_combine).

[matejam]

Minor changes in CombinerHelper.cpp and in the tests.

[matejam]

Use mi_match for comparing instructions instead of comparing the opcodes.

[matejam]

Rebased.

[matejam]

Use m_MInstr instead of m_Reg in matching patterns (mi_match).
Instead of getting MachineInstr's, get only the Register values (no need for MachineInstr in this case).
A few minor bug fixes.
Formatting and refactoring.

[matejam]

Use applyBuildFn instead of writing my own apply.

[matejam]

Changes in tests.

[mbrkusanin]

LGTM

[matejam]

Added missing comments and an FMA combiner group in table gen.

llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h

       MachineInstr &MI,
       std::tuple<Register, Register, Register, unsigned, bool> &MatchInfo);
 
+  /// Transform (fsub (fpext (fmul x, y)), z)
+  ///           -> (fma (fpext x), (fpext y), (fneg z))
+  ///           -> (fmad (fpext x), (fpext y), (fneg z))
+  bool matchCombineFSubFpExtFMulToFMadOrFMA(
+      MachineInstr &MI,
+      std::tuple<Register, Register, Register, unsigned, bool> &MatchInfo);
+  bool applyCombineFSubFpExtFMulToFMadOrFMA(
+      MachineInstr &MI,
+      std::tuple<Register, Register, Register, unsigned, bool> &MatchInfo);
+
   /// Transform trunc ([asz]ext x) to x or ([asz]ext x) or (trunc x).
   bool matchCombineTruncOfExt(MachineInstr &MI,
                               std::pair<Register, unsigned> &MatchInfo);

llvm/include/llvm/Target/GlobalISel/Combine.td

   (apply [{ return Helper.applyCombineFSubFNegFMulToFMadOrFMA(*${root},
                                                               ${info}); }])>;
 
+// Transform (fsub (fpext (fmul x, y)), z) ->
+//           (fma (fpext x), (fpext y), (fneg z))
+def combine_fsub_fpext_fmul_to_fmad_or_fma_info :
+    GIDefMatchData<"std::tuple<Register, Register, Register, unsigned, bool>">;
+def combine_fsub_fpext_fmul_to_fmad_or_fma: GICombineRule<
+  (defs root:$root, combine_fsub_fpext_fmul_to_fmad_or_fma_info:$info),
+  (match (wip_match_opcode G_FSUB):$root,
+         [{ return Helper.matchCombineFSubFpExtFMulToFMadOrFMA(*${root},
+                                                               ${info}); }]),
+  (apply [{ return Helper.applyCombineFSubFpExtFMulToFMadOrFMA(*${root},
+                                                               ${info}); }])>;
+
 // Currently only the one combine above.
 def insert_vec_elt_combines : GICombineGroup<
                             [combine_insert_vec_elts_build_vector]>;

     shift_immed_chain, shift_of_shifted_logic_chain, load_or_combine,
     combine_fadd_fmul_to_fmad_or_fma, combine_fadd_fpext_fmul_to_fmad_or_fma,
     combine_fadd_fma_fmul_to_fmad_or_fma, combine_fadd_fpext_fma_fmul_to_fmad_or_fma,
-    combine_fsub_fmul_to_fmad_or_fma, combine_fsub_fneg_fmul_to_fmad_or_fma]>;
+    combine_fsub_fmul_to_fmad_or_fma, combine_fsub_fneg_fmul_to_fmad_or_fma,
+    combine_fsub_fpext_fmul_to_fmad_or_fma]>;

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

   return true;
 }
 
+bool CombinerHelper::matchCombineFSubFpExtFMulToFMadOrFMA(
+    MachineInstr &MI,
+    std::tuple<Register, Register, Register, unsigned, bool> &MatchInfo) {
+  assert(MI.getOpcode() == TargetOpcode::G_FSUB);
+
+  auto *MF = MI.getParent()->getParent();
+  const auto &TLI = *MF->getSubtarget().getTargetLowering();
+  const TargetOptions &Options = MF->getTarget().Options;
+  LLT DstType = MRI.getType(MI.getOperand(0).getReg());
+  LLT SrcType = MRI.getType(MI.getOperand(1).getReg());
+  MachineInstr *MI0 = MRI.getVRegDef(MI.getOperand(1).getReg());
+  MachineInstr *MI1 = MRI.getVRegDef(MI.getOperand(2).getReg());
+
+  bool LegalOperations =
+      isLegal({TargetOpcode::G_FADD, {DstType, SrcType}});
+  // Floating-point multiply-add with intermediate rounding.
+  bool HasFMAD = (LegalOperations && TLI.isFMADLegal(MI, DstType));
+  // Floating-point multiply-add without intermediate rounding.
+  bool HasFMA =
+      TLI.isFMAFasterThanFMulAndFAdd(*MF, DstType) &&
+      (!LegalOperations || isLegal({TargetOpcode::G_FMA, {DstType, SrcType}}));
+
+  // No valid opcode, do not combine.
+  if (!HasFMAD && !HasFMA)
+    return false;
+
+  bool CanFuse =
+      Options.UnsafeFPMath || MI.getFlag(MachineInstr::MIFlag::FmContract);
+  bool AllowFusionGlobally =
+      (Options.AllowFPOpFusion == FPOpFusion::Fast || CanFuse || HasFMAD);
+
+  // If the addition is not contractable, do not combine.
+  if (!AllowFusionGlobally && !MI.getFlag(MachineInstr::MIFlag::FmContract))
+    return false;
+
+  unsigned PreferredFusedOpcode =
+      HasFMAD ? TargetOpcode::G_FMAD : TargetOpcode::G_FMA;
+  bool Aggressive = TLI.enableAggressiveFMAFusion(DstType);
+
+  // fold (fsub (fpext (fmul x, y)), z) -> (fma (fpext x), (fpext y), (fneg z))
+  if (MI0->getOpcode() == TargetOpcode::G_FPEXT &&
+      (Aggressive || MRI.hasOneNonDBGUse(MI1->getOperand(0).getReg()))) {
+    MachineInstr *MI00 = MRI.getVRegDef(MI0->getOperand(1).getReg());
+    if (isContractableFMul(*MI00, AllowFusionGlobally)) {
+      MatchInfo = {MI00->getOperand(1).getReg(),
+                   MI00->getOperand(2).getReg(),
+                   MI1->getOperand(0).getReg(),
+                   PreferredFusedOpcode,
+                   true};
+      return true;
+    }
+  }
+
+  // fold (fsub x, (fpext (fmul y, z))) -> (fma (fneg (fpext y)), (fpext z), x)
+  if (MI1->getOpcode() == TargetOpcode::G_FPEXT &&
+      (Aggressive || MRI.hasOneNonDBGUse(MI1->getOperand(0).getReg()))) {
+    MachineInstr *MI10 = MRI.getVRegDef(MI1->getOperand(1).getReg());
+    if (isContractableFMul(*MI10, AllowFusionGlobally)) {
+      MatchInfo = {MI10->getOperand(1).getReg(),
+                   MI10->getOperand(2).getReg(),
+                   MI0->getOperand(0).getReg(),
+                   PreferredFusedOpcode,
+                   false};
+      return true;
+    }
+  }
+
+  return false;
+}
+
+bool CombinerHelper::applyCombineFSubFpExtFMulToFMadOrFMA(
+    MachineInstr &MI,
+    std::tuple<Register, Register, Register, unsigned, bool> &MatchInfo) {
+  Register Src1, Src2, Src3;
+  unsigned PreferredFusedOpcode;
+  bool HasFirstFMUL;
+  std::tie(Src1, Src2, Src3, PreferredFusedOpcode, HasFirstFMUL) = MatchInfo;
+
+  Builder.setInstrAndDebugLoc(MI);
+
+  LLT DstTy = MRI.getType(MI.getOperand(0).getReg());
+  if (HasFirstFMUL) {
+    Src1 = Builder.buildFPExt(DstTy, Src1).getReg(0);
+    Src2 = Builder.buildFPExt(DstTy, Src2).getReg(0);
+    Src3 = Builder.buildFNeg(DstTy, Src3).getReg(0);
+  } else {
+    Register FpExtSrc1 = Builder.buildFPExt(DstTy, Src1).getReg(0);
+    Src1 = Builder.buildFNeg(DstTy, FpExtSrc1).getReg(0);
+    Src2 = Builder.buildFPExt(DstTy, Src2).getReg(0);
+  }
+
+  Builder.buildInstr(PreferredFusedOpcode,
+                     {MI.getOperand(0).getReg()}, {Src1, Src2, Src3});
+  MI.eraseFromParent();
+  return true;
+}
+
 bool CombinerHelper::tryCombine(MachineInstr &MI) {
   if (tryCombineCopy(MI))
     return true;

llvm/test/CodeGen/AMDGPU/GlobalISel/combine-fma-sub-ext-mul.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -global-isel -march=amdgcn -mcpu=gfx900 --denormal-fp-math=preserve-sign < %s | FileCheck -check-prefix=GFX9-DENORM %s
+; RUN: llc -global-isel -march=amdgcn -mcpu=gfx1010 --denormal-fp-math=preserve-sign < %s | FileCheck -check-prefix=GFX10-DENORM %s
+
+; fold (fsub (fpext (fmul x, y)), z) -> (fma (fpext x), (fpext y), (fneg z))
+define amdgpu_vs float @test_f16_to_f32_sub_ext_mul(half %x, half %y, float %z) {
+; GFX9-DENORM-LABEL: test_f16_to_f32_sub_ext_mul:
+; GFX9-DENORM:       ; %bb.0: ; %entry
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_e32 v0, v0
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_e32 v1, v1
+; GFX9-DENORM-NEXT:    v_mad_f32 v0, v0, v1, -v2
+; GFX9-DENORM-NEXT:    ; return to shader part epilog
+;
+; GFX10-DENORM-LABEL: test_f16_to_f32_sub_ext_mul:
+; GFX10-DENORM:       ; %bb.0: ; %entry
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v0, v0
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v1, v1
+; GFX10-DENORM-NEXT:    v_fma_f32 v0, v0, v1, -v2
+; GFX10-DENORM-NEXT:    ; return to shader part epilog
+entry:
+  %a = fmul fast half %x, %y
+  %b = fpext half %a to float
+  %c = fsub fast float %b, %z
+  ret float %c
+}
+
+; fold (fsub x, (fpext (fmul y, z))) -> (fma (fneg (fpext y)), (fpext z), x)
+define amdgpu_vs float @test_f16_to_f32_sub_ext_mul_rhs(float %x, half %y, half %z) {
+; GFX9-DENORM-LABEL: test_f16_to_f32_sub_ext_mul_rhs:
+; GFX9-DENORM:       ; %bb.0: ; %.entry
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_e32 v1, v1
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_e32 v2, v2
+; GFX9-DENORM-NEXT:    v_mad_f32 v0, -v1, v2, v0
+; GFX9-DENORM-NEXT:    ; return to shader part epilog
+;
+; GFX10-DENORM-LABEL: test_f16_to_f32_sub_ext_mul_rhs:
+; GFX10-DENORM:       ; %bb.0: ; %.entry
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v1, v1
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v2, v2
+; GFX10-DENORM-NEXT:    v_fmac_f32_e64 v0, -v1, v2
+; GFX10-DENORM-NEXT:    ; return to shader part epilog
+.entry:
+  %a = fmul fast half %y, %z
+  %b = fpext half %a to float
+  %c = fsub fast float %x, %b
+  ret float %c
+}
+
+; fold (fsub (fpext (fmul x, y)), z) -> (fma (fpext x), (fpext y), (fneg z))
+define amdgpu_vs <4 x float> @test_v4f16_to_v4f32_sub_ext_mul(<4 x half> %x, <4 x half> %y, <4 x float> %z) {
+; GFX9-DENORM-LABEL: test_v4f16_to_v4f32_sub_ext_mul:
+; GFX9-DENORM:       ; %bb.0: ; %entry
+; GFX9-DENORM-NEXT:    v_pk_mul_f16 v0, v0, v2
+; GFX9-DENORM-NEXT:    v_pk_mul_f16 v1, v1, v3
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_e32 v2, v0
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_sdwa v3, v0 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_e32 v8, v1
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_sdwa v9, v1 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX9-DENORM-NEXT:    v_sub_f32_e32 v0, v2, v4
+; GFX9-DENORM-NEXT:    v_sub_f32_e32 v1, v3, v5
+; GFX9-DENORM-NEXT:    v_sub_f32_e32 v2, v8, v6
+; GFX9-DENORM-NEXT:    v_sub_f32_e32 v3, v9, v7
+; GFX9-DENORM-NEXT:    ; return to shader part epilog
+;
+; GFX10-DENORM-LABEL: test_v4f16_to_v4f32_sub_ext_mul:
+; GFX10-DENORM:       ; %bb.0: ; %entry
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v15, v0
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_sdwa v19, v0 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v14, v2
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v23, v1
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_sdwa v10, v1 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_sdwa v18, v2 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v9, v3
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_sdwa v13, v3 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX10-DENORM-NEXT:    v_fma_f32 v0, v15, v14, -v4
+; GFX10-DENORM-NEXT:    v_fma_f32 v1, v19, v18, -v5
+; GFX10-DENORM-NEXT:    v_fma_f32 v2, v23, v9, -v6
+; GFX10-DENORM-NEXT:    v_fma_f32 v3, v10, v13, -v7
+; GFX10-DENORM-NEXT:    ; return to shader part epilog
+entry:
+  %a = fmul fast <4 x half> %x, %y
+  %b = fpext <4 x half> %a to <4 x float>
+  %c = fsub fast <4 x float> %b, %z
+  ret <4 x float> %c
+}
+
+; fold (fsub x, (fpext (fmul y, z))) -> (fma (fneg (fpext y)), (fpext z), x)
+define amdgpu_vs <4 x float> @test_v4f16_to_v4f32_sub_ext_mul_rhs(<4 x float> %x, <4 x half> %y, <4 x half> %z) {
+; GFX9-DENORM-LABEL: test_v4f16_to_v4f32_sub_ext_mul_rhs:
+; GFX9-DENORM:       ; %bb.0: ; %.entry
+; GFX9-DENORM-NEXT:    v_pk_mul_f16 v4, v4, v6
+; GFX9-DENORM-NEXT:    v_pk_mul_f16 v5, v5, v7
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_e32 v6, v4
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_e32 v7, v5
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_sdwa v4, v4 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX9-DENORM-NEXT:    v_cvt_f32_f16_sdwa v5, v5 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX9-DENORM-NEXT:    v_sub_f32_e32 v0, v0, v6
+; GFX9-DENORM-NEXT:    v_sub_f32_e32 v2, v2, v7
+; GFX9-DENORM-NEXT:    v_sub_f32_e32 v1, v1, v4
+; GFX9-DENORM-NEXT:    v_sub_f32_e32 v3, v3, v5
+; GFX9-DENORM-NEXT:    ; return to shader part epilog
+;
+; GFX10-DENORM-LABEL: test_v4f16_to_v4f32_sub_ext_mul_rhs:
+; GFX10-DENORM:       ; %bb.0: ; %.entry
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v15, v4
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v10, v6
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v9, v5
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_e32 v11, v7
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_sdwa v4, v4 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_sdwa v6, v6 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_sdwa v5, v5 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX10-DENORM-NEXT:    v_cvt_f32_f16_sdwa v14, v7 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
+; GFX10-DENORM-NEXT:    v_fmac_f32_e64 v0, -v15, v10
+; GFX10-DENORM-NEXT:    v_fmac_f32_e64 v2, -v9, v11
+; GFX10-DENORM-NEXT:    v_fmac_f32_e64 v1, -v4, v6
+; GFX10-DENORM-NEXT:    v_fmac_f32_e64 v3, -v5, v14
+; GFX10-DENORM-NEXT:    ; return to shader part epilog
+.entry:
+  %a = fmul fast <4 x half> %y, %z
+  %b = fpext <4 x half> %a to <4 x float>
+  %c = fsub fast <4 x float> %x, %b
+  ret <4 x float> %c
+}