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//===--- DiagnosticDeadFunctionElimination.cpp ----------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2023 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
//
//===----------------------------------------------------------------------===//
///
/// Delete functions that early diagnostic specialization passes mark as being
/// able to be DCE-ed if there are no further uses. This prevents later
/// diagnostic passes from emitting diagnostics both on the original function
/// and the diagnostic function.
///
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "sil-diagnostic-dead-function-eliminator"
#include "swift/AST/SemanticAttrs.h"
#include "swift/SIL/SILBuilder.h"
#include "swift/SILOptimizer/PassManager/Passes.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "llvm/Support/Debug.h"
using namespace swift;
//===----------------------------------------------------------------------===//
// MARK: Top Level Entrypoint
//===----------------------------------------------------------------------===//
namespace {
struct DiagnosticDeadFunctionEliminator : SILFunctionTransform {
void run() override {
auto *fn = getFunction();
// If an earlier pass asked us to eliminate the function body if it's
// unused, and the function is in fact unused, do that now.
if (!fn->hasSemanticsAttr(semantics::DELETE_IF_UNUSED) ||
fn->getRefCount() != 0 ||
isPossiblyUsedExternally(fn->getLinkage(),
fn->getModule().isWholeModule())) {
return;
}
LLVM_DEBUG(llvm::dbgs()
<< "===> Stubbifying unused function " << fn->getName()
<< "'s body that was marked for deletion\n");
// Remove all non-entry blocks.
auto entryBB = fn->begin();
auto nextBB = std::next(entryBB);
while (nextBB != fn->end()) {
auto thisBB = nextBB;
++nextBB;
thisBB->eraseFromParent();
}
// Rewrite the entry block to only contain an unreachable.
auto loc = entryBB->begin()->getLoc();
entryBB->eraseAllInstructions(fn->getModule());
{
SILBuilder b(&*entryBB);
b.createUnreachable(loc);
}
// If the function has shared linkage, reduce this version to private
// linkage, because we don't want the deleted-body form to win in any
// ODR shootouts.
if (fn->getLinkage() == SILLinkage::Shared) {
fn->setLinkage(SILLinkage::Private);
fn->setSerializedKind(IsNotSerialized);
}
invalidateAnalysis(SILAnalysis::InvalidationKind::FunctionBody);
}
};
} // namespace
SILTransform *swift::createDiagnosticDeadFunctionElimination() {
return new DiagnosticDeadFunctionEliminator();
}
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