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Auto merge of #115641 - durin42:llvm-18-fatlto-take-2, r=nikic

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lto: load bitcode sections by name

Upstream change
llvm/llvm-project@6b539f5eb8 changed `isSectionBitcode` works and it now only respects `.llvm.lto` sections instead of also `.llvmbc`, which it says was never intended to be used for LTO. We instead load sections by name, and sniff for raw bitcode by hand.

This is an alternative approach to #115136, where we tried the same thing using the `object` crate, but it got too fraught to continue.

r? `@nikic`
`@rustbot` label: +llvm-main
This commit is contained in:
bors 2023-09-08 19:07:17 +00:00
commit ffc48e3eda
4 changed files with 89 additions and 16 deletions
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33
compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
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@ -1,5 +1,6 @@
#include <stdio.h>
#include <cstddef>
#include <iomanip>
#include <vector>
#include <set>
@ -1558,6 +1559,38 @@ LLVMRustGetBitcodeSliceFromObjectData(const char *data,
return BitcodeOrError->getBufferStart();
}
// Find a section of an object file by name. Fail if the section is missing or
// empty.
extern "C" const char *LLVMRustGetSliceFromObjectDataByName(const char *data,
size_t len,
const char *name,
size_t *out_len) {
*out_len = 0;
StringRef Data(data, len);
MemoryBufferRef Buffer(Data, ""); // The id is unused.
file_magic Type = identify_magic(Buffer.getBuffer());
Expected<std::unique_ptr<object::ObjectFile>> ObjFileOrError =
object::ObjectFile::createObjectFile(Buffer, Type);
if (!ObjFileOrError) {
LLVMRustSetLastError(toString(ObjFileOrError.takeError()).c_str());
return nullptr;
}
for (const object::SectionRef &Sec : (*ObjFileOrError)->sections()) {
Expected<StringRef> Name = Sec.getName();
if (Name && *Name == name) {
Expected<StringRef> SectionOrError = Sec.getContents();
if (!SectionOrError) {
LLVMRustSetLastError(toString(SectionOrError.takeError()).c_str());
return nullptr;
}
*out_len = SectionOrError->size();
return SectionOrError->data();
}
}
LLVMRustSetLastError("could not find requested section");
return nullptr;
}
// Computes the LTO cache key for the provided 'ModId' in the given 'Data',
// storing the result in 'KeyOut'.
// Currently, this cache key is a SHA-1 hash of anything that could affect