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Auto merge of #98162 - nextsilicon:support_lto_embed_bitcode, r=davidtwco

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Allow to disable thinLTO buffer to support lto-embed-bitcode lld feature

Hello
This change is to fix issue (https://github.com/rust-lang/rust/issues/84395) in which passing "-lto-embed-bitcode=optimized" to lld when linking rust code via linker-plugin-lto doesn't produce the expected result.

Instead of emitting a single unified module into a llvmbc section of the linked elf, it emits multiple submodules.
This is caused because rustc emits the BC modules after running llvm `createWriteThinLTOBitcodePass` pass.
Which in turn triggers a thinLTO linkage and causes the said issue.

This patch allows via compiler flag (-Cemit-thin-lto=<bool>) to select between running `createWriteThinLTOBitcodePass` and `createBitcodeWriterPass`.
Note this pattern of selecting between those 2 passes is common inside of LLVM code.
The default is to match the old behavior.
This commit is contained in:
bors 2022-07-21 10:13:59 +00:00
commit 74f600b990
10 changed files with 32 additions and 7 deletions
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9
compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
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@ -34,6 +34,7 @@
#include "llvm/Transforms/Utils/AddDiscriminators.h"
#include "llvm/Transforms/Utils/FunctionImportUtils.h"
#include "llvm/LTO/LTO.h"
#include "llvm/Bitcode/BitcodeWriterPass.h"
#include "llvm-c/Transforms/PassManagerBuilder.h"
#include "llvm/Transforms/Instrumentation.h"
@ -1638,13 +1639,17 @@ struct LLVMRustThinLTOBuffer {
};
extern "C" LLVMRustThinLTOBuffer*
LLVMRustThinLTOBufferCreate(LLVMModuleRef M) {
LLVMRustThinLTOBufferCreate(LLVMModuleRef M, bool is_thin) {
auto Ret = std::make_unique<LLVMRustThinLTOBuffer>();
{
raw_string_ostream OS(Ret->data);
{
legacy::PassManager PM;
PM.add(createWriteThinLTOBitcodePass(OS));
if (is_thin) {
PM.add(createWriteThinLTOBitcodePass(OS));
} else {
PM.add(createBitcodeWriterPass(OS));
}
PM.run(*unwrap(M));
}
}