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Merge pull request swiftlang#59665 from eeckstein/target-constprop
SILOptimizer: add a pass to perform target specific constant folding.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,142 @@ | ||
| //===--- TargetConstantFolding.cpp ----------------------------------------===// | ||
| // | ||
| // This source file is part of the Swift.org open source project | ||
| // | ||
| // Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors | ||
| // Licensed under Apache License v2.0 with Runtime Library Exception | ||
| // | ||
| // See https://swift.org/LICENSE.txt for license information | ||
| // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors | ||
| // | ||
| // This pass lowers loadable SILTypes. On completion, the SILType of every | ||
| // function argument is an address instead of the type itself. | ||
| // This reduces the code size. | ||
| // Consequently, this pass is required for IRGen. | ||
| // It is a mandatory IRGen preparation pass (not a diagnostic pass). | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #define DEBUG_TYPE "target-constant-folding" | ||
| #include "IRGenModule.h" | ||
| #include "swift/SIL/SILBuilder.h" | ||
| #include "swift/SILOptimizer/PassManager/Transforms.h" | ||
| #include "swift/SILOptimizer/Utils/InstructionDeleter.h" | ||
| #include "llvm/Support/Debug.h" | ||
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| using namespace swift; | ||
| using namespace swift::irgen; | ||
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| namespace { | ||
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| /// Performs constant folding for target-specific values. | ||
| /// | ||
| /// Specifically, this optimization constant folds | ||
| /// ``` | ||
| /// MemoryLayout<S>.size | ||
| /// MemoryLayout<S>.alignment | ||
| /// MemoryLayout<S>.stride | ||
| /// ``` | ||
| /// Constant folding those expressions in the middle of the SIL pipeline | ||
| /// enables other optimizations to e.g. allow such expressions in statically | ||
| /// allocated global variables (done by the GlobalOpt pass). | ||
| class TargetConstantFolding : public SILModuleTransform { | ||
| private: | ||
| /// The entry point to the transformation. | ||
| void run() override { | ||
| auto *irgenOpts = getModule()->getIRGenOptionsOrNull(); | ||
| if (!irgenOpts) | ||
| return; | ||
|
|
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| // We need an IRGenModule to get the actual sizes from type lowering. | ||
| // Creating an IRGenModule involves some effort. Therefore this is a | ||
| // module pass rather than a function pass so that this one-time setup | ||
| // only needs to be done once and not for all functions in a module. | ||
| IRGenerator irgen(*irgenOpts, *getModule()); | ||
| auto targetMachine = irgen.createTargetMachine(); | ||
| if (!targetMachine) | ||
| return; | ||
| IRGenModule IGM(irgen, std::move(targetMachine)); | ||
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| // Scan all instructions in the module for constant foldable instructions. | ||
| for (SILFunction &function : *getModule()) { | ||
|
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| if (!function.shouldOptimize()) | ||
| continue; | ||
|
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| bool changed = false; | ||
| for (SILBasicBlock &block : function) { | ||
| InstructionDeleter deleter; | ||
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| for (SILInstruction *inst : deleter.updatingRange(&block)) { | ||
| if (constFold(inst, IGM)) { | ||
| deleter.forceDelete(inst); | ||
| changed = true; | ||
| } | ||
| } | ||
| deleter.cleanupDeadInstructions(); | ||
| } | ||
| if (changed) { | ||
| invalidateAnalysis(&function, SILAnalysis::InvalidationKind::Instructions); | ||
| } | ||
| } | ||
| } | ||
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| /// Constant fold a single instruction. | ||
| /// | ||
| /// Returns true if `inst` was replaced and can be deleted. | ||
| bool constFold(SILInstruction *inst, IRGenModule &IGM) { | ||
| auto *bi = dyn_cast<BuiltinInst>(inst); | ||
| if (!bi) | ||
| return false; | ||
|
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| llvm::Constant *c = nullptr; | ||
| uint64_t offset = 0; | ||
|
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| switch (bi->getBuiltinInfo().ID) { | ||
| case BuiltinValueKind::Sizeof: | ||
| c = getTypeInfoOfBuiltin(bi, IGM).getStaticSize(IGM); | ||
| break; | ||
| case BuiltinValueKind::Alignof: | ||
| c = getTypeInfoOfBuiltin(bi, IGM).getStaticAlignmentMask(IGM); | ||
| // The constant is the alignment _mask_. We get the actual alignment by | ||
| // adding 1. | ||
| offset = 1; | ||
| break; | ||
| case BuiltinValueKind::Strideof: | ||
| c = getTypeInfoOfBuiltin(bi, IGM).getStaticStride(IGM); | ||
| break; | ||
| default: | ||
| return false; | ||
| } | ||
| auto *intConst = dyn_cast_or_null<llvm::ConstantInt>(c); | ||
| if (!intConst) | ||
| return false; | ||
|
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| APInt value = intConst->getValue(); | ||
| value += APInt(value.getBitWidth(), offset); | ||
| auto intTy = bi->getType().getAs<BuiltinIntegerType>(); | ||
| if (!intTy) | ||
| return false; | ||
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| value = value.sextOrTrunc(intTy->getGreatestWidth()); | ||
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| // Replace the builtin by an integer literal. | ||
| SILBuilderWithScope builder(bi); | ||
| auto *intLit = builder.createIntegerLiteral(bi->getLoc(), bi->getType(), | ||
| value); | ||
| bi->replaceAllUsesWith(intLit); | ||
| return true; | ||
| } | ||
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| const TypeInfo &getTypeInfoOfBuiltin(BuiltinInst *bi, IRGenModule &IGM) { | ||
| SubstitutionMap subs = bi->getSubstitutions(); | ||
| SILType lowered = IGM.getLoweredType(subs.getReplacementTypes()[0]); | ||
| return IGM.getTypeInfo(lowered); | ||
| } | ||
| }; | ||
|
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| } // end anonymous namespace | ||
|
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| SILTransform *swift::createTargetConstantFolding() { | ||
| return new TargetConstantFolding(); | ||
| } |
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