Auto merge of #133250 - DianQK:embed-bitcode-pgo, r=nikic

The embedded bitcode should always be prepared for LTO/ThinLTO

Fixes #115344. Fixes #117220.

There are currently two methods for generating bitcode that used for LTO. One method involves using `-C linker-plugin-lto` to emit object files as bitcode, which is the typical setting used by cargo. The other method is through `-C embed-bitcode=yes`.

When using with `-C embed-bitcode=yes -C lto=no`, we run a complete non-LTO LLVM pipeline to obtain bitcode, then the bitcode is used for LTO. We run the Call Graph Profile Pass twice on the same module.

This PR is doing something similar to LLVM's `buildFatLTODefaultPipeline`, obtaining the bitcode for embedding after running `buildThinLTOPreLinkDefaultPipeline`.

r? nikic

1 files changed, 6 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index f008bd12ed8..c8bb229998e 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -278,6 +278,10 @@ impl ModuleConfig {
             || self.emit_obj == EmitObj::Bitcode
             || self.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full)
     }
+
+    pub fn embed_bitcode(&self) -> bool {
+        self.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full)
+    }
 }
 
 /// Configuration passed to the function returned by the `target_machine_factory`.
@@ -877,14 +881,14 @@ pub(crate) fn compute_per_cgu_lto_type(
 
 fn execute_optimize_work_item<B: ExtraBackendMethods>(
     cgcx: &CodegenContext<B>,
-    module: ModuleCodegen<B::Module>,
+    mut module: ModuleCodegen<B::Module>,
     module_config: &ModuleConfig,
 ) -> Result<WorkItemResult<B>, FatalError> {
     let dcx = cgcx.create_dcx();
     let dcx = dcx.handle();
 
     unsafe {
-        B::optimize(cgcx, dcx, &module, module_config)?;
+        B::optimize(cgcx, dcx, &mut module, module_config)?;
     }
 
     // After we've done the initial round of optimizations we need to