| 1 | //===- CanonicalizeAliases.cpp - ThinLTO Support: Canonicalize Aliases ----===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | // |
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| 9 | // Currently this file implements partial alias canonicalization, to |
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| 10 | // flatten chains of aliases (also done by GlobalOpt, but not on for |
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| 11 | // O0 compiles). E.g. |
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| 12 | // @a = alias i8, i8 *@b |
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| 13 | // @b = alias i8, i8 *@g |
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| 14 | // |
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| 15 | // will be converted to: |
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| 16 | // @a = alias i8, i8 *@g <-- @a is now an alias to base object @g |
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| 17 | // @b = alias i8, i8 *@g |
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| 18 | // |
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| 19 | // Eventually this file will implement full alias canonicalization, so that |
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| 20 | // all aliasees are private anonymous values. E.g. |
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| 21 | // @a = alias i8, i8 *@g |
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| 22 | // @g = global i8 0 |
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| 23 | // |
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| 24 | // will be converted to: |
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| 25 | // @0 = private global |
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| 26 | // @a = alias i8, i8* @0 |
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| 27 | // @g = alias i8, i8* @0 |
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| 28 | // |
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| 29 | // This simplifies optimization and ThinLTO linking of the original symbols. |
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| 30 | //===----------------------------------------------------------------------===// |
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| 31 | |
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| 32 | #include "llvm/Transforms/Utils/CanonicalizeAliases.h" |
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| 33 | #include "llvm/IR/Constants.h" |
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| 34 | |
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| 35 | using namespace llvm; |
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| 36 | |
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| 37 | namespace { |
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| 38 | |
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| 39 | static Constant *canonicalizeAlias(Constant *C, bool &Changed) { |
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| 40 | if (auto *GA = dyn_cast<GlobalAlias>(Val: C)) { |
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| 41 | auto *NewAliasee = canonicalizeAlias(C: GA->getAliasee(), Changed); |
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| 42 | if (NewAliasee != GA->getAliasee()) { |
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| 43 | GA->setAliasee(NewAliasee); |
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| 44 | Changed = true; |
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| 45 | } |
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| 46 | return NewAliasee; |
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| 47 | } |
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| 48 | |
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| 49 | auto *CE = dyn_cast<ConstantExpr>(Val: C); |
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| 50 | if (!CE) |
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| 51 | return C; |
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| 52 | |
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| 53 | std::vector<Constant *> Ops; |
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| 54 | for (Use &U : CE->operands()) |
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| 55 | Ops.push_back(x: canonicalizeAlias(C: cast<Constant>(Val&: U), Changed)); |
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| 56 | return CE->getWithOperands(Ops); |
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| 57 | } |
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| 58 | |
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| 59 | /// Convert aliases to canonical form. |
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| 60 | static bool canonicalizeAliases(Module &M) { |
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| 61 | bool Changed = false; |
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| 62 | for (auto &GA : M.aliases()) |
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| 63 | canonicalizeAlias(C: &GA, Changed); |
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| 64 | return Changed; |
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| 65 | } |
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| 66 | } // anonymous namespace |
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| 67 | |
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| 68 | PreservedAnalyses CanonicalizeAliasesPass::run(Module &M, |
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| 69 | ModuleAnalysisManager &AM) { |
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| 70 | if (!canonicalizeAliases(M)) |
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| 71 | return PreservedAnalyses::all(); |
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| 72 | |
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| 73 | return PreservedAnalyses::none(); |
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| 74 | } |
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| 75 | |
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