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https://gitee.com/openharmony/third_party_spirv-tools
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Fold multiply and subtraction into FMA with negation (#4808)
This change adds a folding rule which transforms x * y - a and a - x * y into FMA(x, y, -a) and FMA(-x, y, a), respectively. While the SPIR-V instruction count remains the same, target instruction sets typically feature FMA instruction variants that can negate an operand. Also this transformation may unlock further optimizations which eliminate the negation. (Google bug: b/226145988)
This commit is contained in:
Nicolas Capens
GitHub
parent
82d91083cb
commit
130a05d2e3
@ -1488,6 +1488,74 @@ bool MergeMulAddArithmetic(IRContext* context, Instruction* inst,
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return false;
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}
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// Replaces |sub| inplace with an FMA instruction |(x*y)+a| where |a| first gets
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// negated if |negate_addition| is true, otherwise |x| gets negated.
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void ReplaceWithFmaAndNegate(Instruction* sub, uint32_t x, uint32_t y,
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uint32_t a, bool negate_addition) {
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uint32_t ext =
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sub->context()->get_feature_mgr()->GetExtInstImportId_GLSLstd450();
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if (ext == 0) {
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sub->context()->AddExtInstImport("GLSL.std.450");
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ext = sub->context()->get_feature_mgr()->GetExtInstImportId_GLSLstd450();
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assert(ext != 0 &&
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"Could not add the GLSL.std.450 extended instruction set");
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}
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InstructionBuilder ir_builder(
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sub->context(), sub,
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IRContext::kAnalysisDefUse | IRContext::kAnalysisInstrToBlockMapping);
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Instruction* neg = ir_builder.AddUnaryOp(sub->type_id(), SpvOpFNegate,
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negate_addition ? a : x);
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uint32_t neg_op = neg->result_id(); // -a : -x
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std::vector<Operand> operands;
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operands.push_back({SPV_OPERAND_TYPE_ID, {ext}});
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operands.push_back({SPV_OPERAND_TYPE_LITERAL_INTEGER, {GLSLstd450Fma}});
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operands.push_back({SPV_OPERAND_TYPE_ID, {negate_addition ? x : neg_op}});
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operands.push_back({SPV_OPERAND_TYPE_ID, {y}});
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operands.push_back({SPV_OPERAND_TYPE_ID, {negate_addition ? neg_op : a}});
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sub->SetOpcode(SpvOpExtInst);
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sub->SetInOperands(std::move(operands));
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}
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// Folds a multiply and subtract into an Fma and negation.
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//
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// Cases:
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// (x * y) - a = Fma x y -a
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// a - (x * y) = Fma -x y a
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bool MergeMulSubArithmetic(IRContext* context, Instruction* sub,
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const std::vector<const analysis::Constant*>&) {
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assert(sub->opcode() == SpvOpFSub);
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if (!sub->IsFloatingPointFoldingAllowed()) {
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return false;
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}
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analysis::DefUseManager* def_use_mgr = context->get_def_use_mgr();
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for (int i = 0; i < 2; i++) {
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uint32_t op_id = sub->GetSingleWordInOperand(i);
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Instruction* mul = def_use_mgr->GetDef(op_id);
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if (mul->opcode() != SpvOpFMul) {
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continue;
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}
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if (!mul->IsFloatingPointFoldingAllowed()) {
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continue;
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}
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uint32_t x = mul->GetSingleWordInOperand(0);
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uint32_t y = mul->GetSingleWordInOperand(1);
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uint32_t a = sub->GetSingleWordInOperand((i + 1) % 2);
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ReplaceWithFmaAndNegate(sub, x, y, a, i == 0);
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return true;
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}
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return false;
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}
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FoldingRule IntMultipleBy1() {
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return [](IRContext*, Instruction* inst,
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const std::vector<const analysis::Constant*>& constants) {
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@ -2831,6 +2899,7 @@ void FoldingRules::AddFoldingRules() {
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rules_[SpvOpFSub].push_back(MergeSubNegateArithmetic());
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rules_[SpvOpFSub].push_back(MergeSubAddArithmetic());
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rules_[SpvOpFSub].push_back(MergeSubSubArithmetic());
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rules_[SpvOpFSub].push_back(MergeMulSubArithmetic);
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rules_[SpvOpIAdd].push_back(RedundantIAdd());
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rules_[SpvOpIAdd].push_back(MergeAddNegateArithmetic());
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@ -7359,7 +7359,7 @@ INSTANTIATE_TEST_SUITE_P(FmaGenerationMatchingTest, MatchingInstructionFoldingTe
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"OpReturn\n" +
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"OpFunctionEnd",
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3, true),
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// Test 5: that the OpExtInstImport instruction is generated if it is missing.
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// Test 4: that the OpExtInstImport instruction is generated if it is missing.
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InstructionFoldingCase<bool>(
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std::string() +
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"; CHECK: [[ext:%\\w+]] = OpExtInstImport \"GLSL.std.450\"\n" +
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@ -7454,7 +7454,63 @@ INSTANTIATE_TEST_SUITE_P(FmaGenerationMatchingTest, MatchingInstructionFoldingTe
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"OpStore %a %3\n" +
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"OpReturn\n" +
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"OpFunctionEnd",
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3, false)
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3, false),
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// Test case 7: (x * y) - a = Fma(x, y, -a)
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InstructionFoldingCase<bool>(
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Header() +
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"; CHECK: [[ext:%\\w+]] = OpExtInstImport \"GLSL.std.450\"\n" +
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"; CHECK: OpFunction\n" +
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"; CHECK: [[x:%\\w+]] = OpVariable {{%\\w+}} Function\n" +
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"; CHECK: [[y:%\\w+]] = OpVariable {{%\\w+}} Function\n" +
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"; CHECK: [[a:%\\w+]] = OpVariable {{%\\w+}} Function\n" +
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"; CHECK: [[lx:%\\w+]] = OpLoad {{%\\w+}} [[x]]\n" +
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"; CHECK: [[ly:%\\w+]] = OpLoad {{%\\w+}} [[y]]\n" +
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"; CHECK: [[la:%\\w+]] = OpLoad {{%\\w+}} [[a]]\n" +
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"; CHECK: [[na:%\\w+]] = OpFNegate {{%\\w+}} [[la]]\n" +
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"; CHECK: [[fma:%\\w+]] = OpExtInst {{%\\w+}} [[ext]] Fma [[lx]] [[ly]] [[na]]\n" +
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"; CHECK: OpStore {{%\\w+}} [[fma]]\n" +
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"%main = OpFunction %void None %void_func\n" +
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"%main_lab = OpLabel\n" +
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"%x = OpVariable %_ptr_float Function\n" +
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"%y = OpVariable %_ptr_float Function\n" +
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"%a = OpVariable %_ptr_float Function\n" +
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"%lx = OpLoad %float %x\n" +
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"%ly = OpLoad %float %y\n" +
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"%mul = OpFMul %float %lx %ly\n" +
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"%la = OpLoad %float %a\n" +
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"%3 = OpFSub %float %mul %la\n" +
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"OpStore %a %3\n" +
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"OpReturn\n" +
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"OpFunctionEnd",
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3, true),
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// Test case 8: a - (x * y) = Fma(-x, y, a)
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InstructionFoldingCase<bool>(
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Header() +
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"; CHECK: [[ext:%\\w+]] = OpExtInstImport \"GLSL.std.450\"\n" +
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"; CHECK: OpFunction\n" +
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"; CHECK: [[x:%\\w+]] = OpVariable {{%\\w+}} Function\n" +
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"; CHECK: [[y:%\\w+]] = OpVariable {{%\\w+}} Function\n" +
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"; CHECK: [[a:%\\w+]] = OpVariable {{%\\w+}} Function\n" +
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"; CHECK: [[lx:%\\w+]] = OpLoad {{%\\w+}} [[x]]\n" +
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"; CHECK: [[ly:%\\w+]] = OpLoad {{%\\w+}} [[y]]\n" +
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"; CHECK: [[la:%\\w+]] = OpLoad {{%\\w+}} [[a]]\n" +
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"; CHECK: [[nx:%\\w+]] = OpFNegate {{%\\w+}} [[lx]]\n" +
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"; CHECK: [[fma:%\\w+]] = OpExtInst {{%\\w+}} [[ext]] Fma [[nx]] [[ly]] [[la]]\n" +
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"; CHECK: OpStore {{%\\w+}} [[fma]]\n" +
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"%main = OpFunction %void None %void_func\n" +
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"%main_lab = OpLabel\n" +
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"%x = OpVariable %_ptr_float Function\n" +
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"%y = OpVariable %_ptr_float Function\n" +
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"%a = OpVariable %_ptr_float Function\n" +
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"%lx = OpLoad %float %x\n" +
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"%ly = OpLoad %float %y\n" +
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"%mul = OpFMul %float %lx %ly\n" +
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"%la = OpLoad %float %a\n" +
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"%3 = OpFSub %float %la %mul\n" +
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"OpStore %a %3\n" +
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"OpReturn\n" +
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"OpFunctionEnd",
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3, true)
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));
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using MatchingInstructionWithNoResultFoldingTest =
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