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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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6
compiler/rustc_codegen_llvm/src/back/lto.rs
View file

@ -199,7 +199,7 @@ pub(crate) fn run_thin(
pub(crate) fn prepare_thin(module: ModuleCodegen<ModuleLlvm>) -> (String, ThinBuffer) {
let name = module.name.clone();
let buffer = ThinBuffer::new(module.module_llvm.llmod());
let buffer = ThinBuffer::new(module.module_llvm.llmod(), true);
(name, buffer)
}
@ -695,9 +695,9 @@ unsafe impl Send for ThinBuffer {}
unsafe impl Sync for ThinBuffer {}
impl ThinBuffer {
pub fn new(m: &llvm::Module) -> ThinBuffer {
pub fn new(m: &llvm::Module, is_thin: bool) -> ThinBuffer {
unsafe {
let buffer = llvm::LLVMRustThinLTOBufferCreate(m);
let buffer = llvm::LLVMRustThinLTOBufferCreate(m, is_thin);
ThinBuffer(buffer)
}
}

2
compiler/rustc_codegen_llvm/src/back/write.rs
View file

@ -790,7 +790,7 @@ pub(crate) unsafe fn codegen(
let _timer = cgcx
.prof
.generic_activity_with_arg("LLVM_module_codegen_make_bitcode", &*module.name);
let thin = ThinBuffer::new(llmod);
let thin = ThinBuffer::new(llmod, config.emit_thin_lto);
let data = thin.data();
if let Some(bitcode_filename) = bc_out.file_name() {

2
compiler/rustc_codegen_llvm/src/llvm/ffi.rs
View file

@ -2470,7 +2470,7 @@ extern "C" {
pub fn LLVMRustModuleBufferFree(p: &'static mut ModuleBuffer);
pub fn LLVMRustModuleCost(M: &Module) -> u64;
pub fn LLVMRustThinLTOBufferCreate(M: &Module) -> &'static mut ThinLTOBuffer;
pub fn LLVMRustThinLTOBufferCreate(M: &Module, is_thin: bool) -> &'static mut ThinLTOBuffer;
pub fn LLVMRustThinLTOBufferFree(M: &'static mut ThinLTOBuffer);
pub fn LLVMRustThinLTOBufferPtr(M: &ThinLTOBuffer) -> *const c_char;
pub fn LLVMRustThinLTOBufferLen(M: &ThinLTOBuffer) -> size_t;