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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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2
compiler/rustc_session/src/options.rs
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@ -1279,6 +1279,8 @@ options! {
"version of DWARF debug information to emit (default: 2 or 4, depending on platform)"),
emit_stack_sizes: bool = (false, parse_bool, [UNTRACKED],
"emit a section containing stack size metadata (default: no)"),
emit_thin_lto: bool = (true, parse_bool, [TRACKED],
"emit the bc module with thin LTO info (default: yes)"),
fewer_names: Option<bool> = (None, parse_opt_bool, [TRACKED],
"reduce memory use by retaining fewer names within compilation artifacts (LLVM-IR) \
(default: no)"),