Auto merge of #88550 - dpaoliello:dpaoliello/allocdebuginfo, r=estebank

Include debug info for the allocator shim

Issue Details:
In some cases it is necessary to generate an "allocator shim" to forward various Rust allocation functions (e.g., `__rust_alloc`) to an underlying function (e.g., `malloc`). However, since this allocator shim is a manually created LLVM module it is not processed via the normal module processing code and so no debug info is generated for it (if debugging info is enabled).

Fix Details:
* Modify the `debuginfo` code to allow creating debug info for a module without a `CodegenCx` (since it is difficult, and expensive, to create one just to emit some debug info).
* After creating the allocator shim add in basic debug info.

2 files changed, 11 insertions, 4 deletions

diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index a5143a755fe..f427dd76693 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -538,12 +538,18 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
     } else if let Some(kind) = tcx.allocator_kind(()) {
         let llmod_id =
             cgu_name_builder.build_cgu_name(LOCAL_CRATE, &["crate"], Some("allocator")).to_string();
-        let mut modules = backend.new_metadata(tcx, &llmod_id);
+        let mut module_llvm = backend.new_metadata(tcx, &llmod_id);
         tcx.sess.time("write_allocator_module", || {
-            backend.codegen_allocator(tcx, &mut modules, kind, tcx.lang_items().oom().is_some())
+            backend.codegen_allocator(
+                tcx,
+                &mut module_llvm,
+                &llmod_id,
+                kind,
+                tcx.lang_items().oom().is_some(),
+            )
         });
 
-        Some(ModuleCodegen { name: llmod_id, module_llvm: modules, kind: ModuleKind::Allocator })
+        Some(ModuleCodegen { name: llmod_id, module_llvm, kind: ModuleKind::Allocator })
     } else {
         None
     };
diff --git a/compiler/rustc_codegen_ssa/src/traits/backend.rs b/compiler/rustc_codegen_ssa/src/traits/backend.rs
index 1393fc71d6b..96e53f51dac 100644
--- a/compiler/rustc_codegen_ssa/src/traits/backend.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/backend.rs
@@ -120,7 +120,8 @@ pub trait ExtraBackendMethods: CodegenBackend + WriteBackendMethods + Sized + Se
     fn codegen_allocator<'tcx>(
         &self,
         tcx: TyCtxt<'tcx>,
-        mods: &mut Self::Module,
+        module_llvm: &mut Self::Module,
+        module_name: &str,
         kind: AllocatorKind,
         has_alloc_error_handler: bool,
     );