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105 lines
3.1 KiB
C++
105 lines
3.1 KiB
C++
//===- CanonicalizeAliases.cpp - ThinLTO Support: Canonicalize Aliases ----===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Currently this file implements partial alias canonicalization, to
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// flatten chains of aliases (also done by GlobalOpt, but not on for
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// O0 compiles). E.g.
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// @a = alias i8, i8 *@b
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// @b = alias i8, i8 *@g
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//
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// will be converted to:
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// @a = alias i8, i8 *@g <-- @a is now an alias to base object @g
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// @b = alias i8, i8 *@g
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//
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// Eventually this file will implement full alias canonicalation, so that
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// all aliasees are private anonymous values. E.g.
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// @a = alias i8, i8 *@g
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// @g = global i8 0
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//
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// will be converted to:
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// @0 = private global
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// @a = alias i8, i8* @0
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// @g = alias i8, i8* @0
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//
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// This simplifies optimization and ThinLTO linking of the original symbols.
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/CanonicalizeAliases.h"
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#include "llvm/IR/Operator.h"
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#include "llvm/IR/ValueHandle.h"
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using namespace llvm;
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namespace {
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static Constant *canonicalizeAlias(Constant *C, bool &Changed) {
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if (auto *GA = dyn_cast<GlobalAlias>(C)) {
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auto *NewAliasee = canonicalizeAlias(GA->getAliasee(), Changed);
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if (NewAliasee != GA->getAliasee()) {
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GA->setAliasee(NewAliasee);
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Changed = true;
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}
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return NewAliasee;
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}
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auto *CE = dyn_cast<ConstantExpr>(C);
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if (!CE)
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return C;
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std::vector<Constant *> Ops;
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for (Use &U : CE->operands())
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Ops.push_back(canonicalizeAlias(cast<Constant>(U), Changed));
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return CE->getWithOperands(Ops);
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}
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/// Convert aliases to canonical form.
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static bool canonicalizeAliases(Module &M) {
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bool Changed = false;
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for (auto &GA : M.aliases())
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canonicalizeAlias(&GA, Changed);
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return Changed;
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}
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// Legacy pass that canonicalizes aliases.
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class CanonicalizeAliasesLegacyPass : public ModulePass {
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public:
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/// Pass identification, replacement for typeid
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static char ID;
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/// Specify pass name for debug output
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StringRef getPassName() const override { return "Canonicalize Aliases"; }
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explicit CanonicalizeAliasesLegacyPass() : ModulePass(ID) {}
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bool runOnModule(Module &M) override { return canonicalizeAliases(M); }
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};
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char CanonicalizeAliasesLegacyPass::ID = 0;
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} // anonymous namespace
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PreservedAnalyses CanonicalizeAliasesPass::run(Module &M,
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ModuleAnalysisManager &AM) {
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if (!canonicalizeAliases(M))
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return PreservedAnalyses::all();
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return PreservedAnalyses::none();
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}
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INITIALIZE_PASS_BEGIN(CanonicalizeAliasesLegacyPass, "canonicalize-aliases",
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"Canonicalize aliases", false, false)
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INITIALIZE_PASS_END(CanonicalizeAliasesLegacyPass, "canonicalize-aliases",
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"Canonicalize aliases", false, false)
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namespace llvm {
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ModulePass *createCanonicalizeAliasesPass() {
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return new CanonicalizeAliasesLegacyPass();
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}
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} // namespace llvm
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