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Explicitly demote Float16 operations to Float32.
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| Original file line number | Diff line number | Diff line change |
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| // This file is a part of Julia. License is MIT: https://julialang.org/license | ||
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| // This pass finds floating-point operations on 16-bit (half precision) values, and replaces | ||
| // them by equivalent operations on 32-bit (single precision) values surrounded by a fpext | ||
| // and fptrunc. This ensures that the exact semantics of IEEE floating-point are preserved. | ||
| // | ||
| // Without this pass, back-ends that do not natively support half-precision (e.g. x86_64) | ||
| // similarly pattern-match half-precision operations with single-precision equivalents, but | ||
| // without truncating after every operation. Doing so breaks floating-point operations that | ||
| // assume precise semantics, such as Dekker arithmetic (as used in twiceprecision.jl). | ||
| // | ||
| // This pass is intended to run late in the pipeline, and should not be followed by | ||
| // instcombine. A run of GVN is recommended to clean-up identical conversions. | ||
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| #include "llvm-version.h" | ||
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| #define DEBUG_TYPE "demote_float16" | ||
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| #include "support/dtypes.h" | ||
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| #include <llvm/IR/IRBuilder.h> | ||
| #include <llvm/IR/LegacyPassManager.h> | ||
| #include <llvm/IR/Module.h> | ||
| #include <llvm/Support/Debug.h> | ||
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| using namespace llvm; | ||
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| namespace { | ||
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| struct DemoteFloat16Pass : public FunctionPass { | ||
| static char ID; | ||
| DemoteFloat16Pass() : FunctionPass(ID){}; | ||
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| private: | ||
| bool runOnFunction(Function &F) override; | ||
| }; | ||
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| bool DemoteFloat16Pass::runOnFunction(Function &F) | ||
| { | ||
| auto &ctx = F.getContext(); | ||
| auto T_float16 = Type::getHalfTy(ctx); | ||
| auto T_float32 = Type::getFloatTy(ctx); | ||
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| SmallVector<Instruction *, 0> erase; | ||
| for (auto &BB : F) { | ||
| for (auto &I : BB) { | ||
| switch (I.getOpcode()) { | ||
| case Instruction::FNeg: | ||
| case Instruction::FAdd: | ||
| case Instruction::FSub: | ||
| case Instruction::FMul: | ||
| case Instruction::FDiv: | ||
| case Instruction::FRem: | ||
| case Instruction::FCmp: | ||
| break; | ||
| default: | ||
| continue; | ||
| } | ||
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| IRBuilder<> builder(&I); | ||
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| // extend Float16 operands to Float32 | ||
| bool OperandsChanged = false; | ||
| SmallVector<Value *, 2> Operands(I.getNumOperands()); | ||
| for (size_t i = 0; i < I.getNumOperands(); i++) { | ||
| Value *Op = I.getOperand(i); | ||
| if (Op->getType() == T_float16) { | ||
| Op = builder.CreateFPExt(Op, T_float32); | ||
| OperandsChanged = true; | ||
| } | ||
| Operands[i] = (Op); | ||
| } | ||
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| // recreate the instruction if any operands changed, | ||
| // truncating the result back to Float16 | ||
| if (OperandsChanged) { | ||
| Value *NewI; | ||
| switch (I.getOpcode()) { | ||
| case Instruction::FNeg: | ||
| assert(Operands.size() == 1); | ||
| NewI = builder.CreateFNeg(Operands[0]); | ||
| break; | ||
| case Instruction::FAdd: | ||
| assert(Operands.size() == 2); | ||
| NewI = builder.CreateFAdd(Operands[0], Operands[1]); | ||
| break; | ||
| case Instruction::FSub: | ||
| assert(Operands.size() == 2); | ||
| NewI = builder.CreateFSub(Operands[0], Operands[1]); | ||
| break; | ||
| case Instruction::FMul: | ||
| assert(Operands.size() == 2); | ||
| NewI = builder.CreateFMul(Operands[0], Operands[1]); | ||
| break; | ||
| case Instruction::FDiv: | ||
| assert(Operands.size() == 2); | ||
| NewI = builder.CreateFDiv(Operands[0], Operands[1]); | ||
| break; | ||
| case Instruction::FRem: | ||
| assert(Operands.size() == 2); | ||
| NewI = builder.CreateFRem(Operands[0], Operands[1]); | ||
| break; | ||
| case Instruction::FCmp: | ||
| assert(Operands.size() == 2); | ||
| NewI = builder.CreateFCmp(cast<FCmpInst>(&I)->getPredicate(), | ||
| Operands[0], Operands[1]); | ||
| break; | ||
| default: | ||
| abort(); | ||
| } | ||
| cast<Instruction>(NewI)->copyMetadata(I); | ||
| cast<Instruction>(NewI)->copyFastMathFlags(&I); | ||
| if (NewI->getType() != I.getType()) | ||
| NewI = builder.CreateFPTrunc(NewI, I.getType()); | ||
| I.replaceAllUsesWith(NewI); | ||
| erase.push_back(&I); | ||
| } | ||
| } | ||
| } | ||
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| if (erase.size() > 0) { | ||
| for (auto V : erase) | ||
| V->eraseFromParent(); | ||
| return true; | ||
| } | ||
| else | ||
| return false; | ||
| } | ||
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| char DemoteFloat16Pass::ID = 0; | ||
| static RegisterPass<DemoteFloat16Pass> | ||
| Y("DemoteFloat16", | ||
| "Demote Float16 operations to Float32 equivalents.", | ||
| false, | ||
| false); | ||
| } | ||
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| Pass *createDemoteFloat16Pass() | ||
| { | ||
| return new DemoteFloat16Pass(); | ||
| } | ||
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| extern "C" JL_DLLEXPORT void LLVMExtraAddDemoteFloat16Pass(LLVMPassManagerRef PM) | ||
| { | ||
| unwrap(PM)->add(createDemoteFloat16Pass()); | ||
| } |