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18063707b5
This new OSSA invariant simplifies many optimizations because they don't have to take care of the corner case of incomplete lifetimes in dead-end blocks. The implementation basically consists of these changes: * add the lifetime completion utility * add a flag in SILFunction which tells optimization that they need to run the lifetime completion utility * let all optimizations complete lifetimes if necessary * enable the ownership verifier to check complete lifetimes
98 lines
3.5 KiB
C++
98 lines
3.5 KiB
C++
//===--- DiagnosticDeadFunctionElimination.cpp ----------------------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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///
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/// Delete functions that early diagnostic specialization passes mark as being
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/// able to be DCE-ed if there are no further uses. This prevents later
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/// diagnostic passes from emitting diagnostics both on the original function
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/// and the diagnostic function.
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///
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "sil-diagnostic-dead-function-eliminator"
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#include "swift/AST/SemanticAttrs.h"
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#include "swift/SIL/SILBuilder.h"
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#include "swift/SILOptimizer/PassManager/Passes.h"
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#include "swift/SILOptimizer/PassManager/Transforms.h"
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#include "llvm/Support/Debug.h"
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using namespace swift;
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//===----------------------------------------------------------------------===//
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// MARK: Top Level Entrypoint
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//===----------------------------------------------------------------------===//
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namespace {
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struct DiagnosticDeadFunctionEliminator : SILFunctionTransform {
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void run() override {
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auto *fn = getFunction();
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auto &mod = fn->getModule();
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// If an earlier pass asked us to eliminate the function body if it's
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// unused, and the function is in fact unused, do that now.
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if (!fn->hasSemanticsAttr(semantics::DELETE_IF_UNUSED) ||
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fn->getRefCount() != 0 ||
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isPossiblyUsedExternally(fn->getLinkage(),
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fn->getModule().isWholeModule())) {
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return;
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}
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LLVM_DEBUG(llvm::dbgs()
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<< "===> Stubbifying unused function " << fn->getName()
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<< "'s body that was marked for deletion\n");
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// Remove all non-entry blocks.
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auto entryBB = fn->begin();
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auto nextBB = std::next(entryBB);
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while (nextBB != fn->end()) {
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auto thisBB = nextBB;
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++nextBB;
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thisBB->eraseFromParent();
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}
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// Rewrite the entry block to only contain an unreachable.
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auto loc = entryBB->begin()->getLoc();
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entryBB->eraseAllInstructions(fn->getModule());
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{
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SILBuilder b(&*entryBB);
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b.createUnreachable(loc);
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}
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// Drop differentiability witnesses, if any
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if (!mod.lookUpDifferentiabilityWitnessesForFunction(fn->getName()).empty())
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mod.eraseAllDifferentiabilityWitnesses(fn);
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// If the function has shared linkage, reduce this version to private
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// linkage, because we don't want the deleted-body form to win in any
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// ODR shootouts.
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if (fn->getLinkage() == SILLinkage::Shared) {
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fn->setLinkage(SILLinkage::Private);
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fn->setSerializedKind(IsNotSerialized);
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}
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invalidateAnalysis(SILAnalysis::InvalidationKind::FunctionBody);
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// We know that this pass does not create infinite loops even if it
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// deletes basic blocks.
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fn->setNeedBreakInfiniteLoops(false);
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// Replacing the whole function with an `unreachable` does not create
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// incomplete lifetimes.
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fn->setNeedCompleteLifetimes(false);
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}
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};
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} // namespace
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SILTransform *swift::createDiagnosticDeadFunctionElimination() {
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return new DiagnosticDeadFunctionEliminator();
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}
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