================ @@ -0,0 +1,150 @@ +//===-- LowerCommentStringPass.cpp - Lower Comment string metadata -------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===---------------------------------------------------------------------===// +// +// This pass lowers the module-level comment string metadata emitted by Clang: +// +// !comment_string.loadtime = !{!"Copyright ..."} +// +// into concrete, translation-unit-local globals. +// This Pass is enabled only for AIX. +// For each module (translation unit), the pass performs the following: +// +// 1. Creates a null-terminated, internal constant string global +// (`__loadtime_comment_str`) containing the copyright text with +// section attribute "__loadtime_comment". The backend places this +// in the .text section of the object file. +// +// 2. Marks the string in `llvm.compiler.used` so it cannot be dropped by +// optimization or LTO. +// +// 3. Attaches `!implicit.ref` metadata referencing the string to every +// defined function in the module. The PowerPC AIX backend recognizes +// this metadata and emits a `.ref` directive from the function to the +// string, creating a concrete relocation that prevents the linker from +// discarding the string (as long as the referencing symbol is kept). +// +// Input IR: +// !comment_string.loadtime = !{!"Copyright"} +// Output IR: +// @__loadtime_comment_str = internal constant [N x i8] c"Copyright\00", +// section "__loadtime_comment" +// @llvm.compiler.used = appending global [1 x ptr] [ptr +// @__loadtime_comment_str] +// +// define i32 @func() !implicit.ref !5 { ... } +// !5 = !{ptr @__loadtime_comment_str} +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/LowerCommentStringPass.h" + +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/StringRef.h" +#include "llvm/IR/Attributes.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GlobalValue.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/MDBuilder.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/Value.h" +#include "llvm/Passes/PassBuilder.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/TargetParser/Triple.h" +#include "llvm/Transforms/Utils/ModuleUtils.h" + +#define DEBUG_TYPE "lower-comment-string" + +using namespace llvm; + +static cl::opt<bool> + DisableCopyrightMetadata("disable-lower-comment-string", cl::ReallyHidden, + cl::desc("Disable LowerCommentString pass."), + cl::init(false)); + +static bool isSupportedTarget(const Module &M) { + Triple T{M.getTargetTriple()}; + return T.isOSAIX(); +} + +PreservedAnalyses LowerCommentStringPass::run(Module &M, + ModuleAnalysisManager &AM) { + if (DisableCopyrightMetadata || !isSupportedTarget(M)) + return PreservedAnalyses::all(); + + LLVMContext &Ctx = M.getContext(); + + // Single-metadata: !comment_string.loadtime = !{!0} + // Each operand node is expected to have one MDString operand. + NamedMDNode *MD = M.getNamedMetadata("comment_string.loadtime"); + if (!MD || MD->getNumOperands() == 0) + return PreservedAnalyses::all(); + + // At this point we are guaranteed that one TU contains a single copyright + // metadata entry. Create TU-local string global for that metadata entry. + MDNode *MdNode = MD->getOperand(0); + if (!MdNode || MdNode->getNumOperands() == 0) + return PreservedAnalyses::all(); + + auto *MdString = dyn_cast_or_null<MDString>(MdNode->getOperand(0)); + if (!MdString) + return PreservedAnalyses::all(); + + StringRef Text = MdString->getString(); + if (Text.empty()) + return PreservedAnalyses::all(); + + // 1. Create a single null-terminated string global. + Constant *StrInit = ConstantDataArray::getString(Ctx, Text, /*AddNull=*/true); + + // Global variable should be Internal, constant, TU-local. ---------------- hubert-reinterpretcast wrote:
```suggestion // The global variable should be internal, constant, and TU-local. ``` https://github.com/llvm/llvm-project/pull/178184 _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
