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debuginfo: split method declaration and definition
When we're adding a method to a type DIE, we only want a DW_AT_declaration there, because LLVM LTO can't unify type definitions when a child DIE is a full subprogram definition. Now the subprogram definition gets added at the CU level with a specification link back to the abstract declaration.
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5 files changed

+109
-34
lines changed

5 files changed

+109
-34
lines changed

‎compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

+51-34
Original file line numberDiff line numberDiff line change
@@ -322,7 +322,7 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
322322
let tcx = self.tcx;
323323

324324
let def_id = instance.def_id();
325-
let containing_scope = get_containing_scope(self, instance);
325+
let (containing_scope, is_method) = get_containing_scope(self, instance);
326326
let span = tcx.def_span(def_id);
327327
let loc = self.lookup_debug_loc(span.lo());
328328
let file_metadata = file_metadata(self, &loc.file);
@@ -378,8 +378,29 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
378378
}
379379
}
380380

381-
unsafe {
382-
return llvm::LLVMRustDIBuilderCreateFunction(
381+
// When we're adding a method to a type DIE, we only want a DW_AT_declaration there, because
382+
// LLVM LTO can't unify type definitions when a child DIE is a full subprogram definition.
383+
// When we use this `decl` below, the subprogram definition gets created at the CU level
384+
// with a DW_AT_specification pointing back to the type's declaration.
385+
let decl = is_method.then(|| unsafe {
386+
llvm::LLVMRustDIBuilderCreateMethod(
387+
DIB(self),
388+
containing_scope,
389+
name.as_ptr().cast(),
390+
name.len(),
391+
linkage_name.as_ptr().cast(),
392+
linkage_name.len(),
393+
file_metadata,
394+
loc.line,
395+
function_type_metadata,
396+
flags,
397+
spflags & !DISPFlags::SPFlagDefinition,
398+
template_parameters,
399+
)
400+
});
401+
402+
return unsafe {
403+
llvm::LLVMRustDIBuilderCreateFunction(
383404
DIB(self),
384405
containing_scope,
385406
name.as_ptr().cast(),
@@ -394,9 +415,9 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
394415
spflags,
395416
maybe_definition_llfn,
396417
template_parameters,
397-
None,
398-
);
399-
}
418+
decl,
419+
)
420+
};
400421

401422
fn get_function_signature<'ll, 'tcx>(
402423
cx: &CodegenCx<'ll, 'tcx>,
@@ -493,14 +514,16 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
493514
names
494515
}
495516

517+
/// Returns a scope, plus `true` if that's a type scope for "class" methods,
518+
/// otherwise `false` for plain namespace scopes.
496519
fn get_containing_scope<'ll, 'tcx>(
497520
cx: &CodegenCx<'ll, 'tcx>,
498521
instance: Instance<'tcx>,
499-
) -> &'ll DIScope {
522+
) -> (&'ll DIScope, bool) {
500523
// First, let's see if this is a method within an inherent impl. Because
501524
// if yes, we want to make the result subroutine DIE a child of the
502525
// subroutine's self-type.
503-
let self_type = cx.tcx.impl_of_method(instance.def_id()).and_then(|impl_def_id| {
526+
if let Some(impl_def_id) = cx.tcx.impl_of_method(instance.def_id()) {
504527
// If the method does *not* belong to a trait, proceed
505528
if cx.tcx.trait_id_of_impl(impl_def_id).is_none() {
506529
let impl_self_ty = cx.tcx.subst_and_normalize_erasing_regions(
@@ -511,39 +534,33 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
511534

512535
// Only "class" methods are generally understood by LLVM,
513536
// so avoid methods on other types (e.g., `<*mut T>::null`).
514-
match impl_self_ty.kind() {
515-
ty::Adt(def, ..) if !def.is_box() => {
516-
// Again, only create type information if full debuginfo is enabled
517-
if cx.sess().opts.debuginfo == DebugInfo::Full
518-
&& !impl_self_ty.has_param()
519-
{
520-
Some(type_di_node(cx, impl_self_ty))
521-
} else {
522-
Some(namespace::item_namespace(cx, def.did()))
523-
}
537+
if let ty::Adt(def, ..) = impl_self_ty.kind() && !def.is_box() {
538+
// Again, only create type information if full debuginfo is enabled
539+
if cx.sess().opts.debuginfo == DebugInfo::Full && !impl_self_ty.has_param()
540+
{
541+
return (type_di_node(cx, impl_self_ty), true);
542+
} else {
543+
return (namespace::item_namespace(cx, def.did()), false);
524544
}
525-
_ => None,
526545
}
527546
} else {
528547
// For trait method impls we still use the "parallel namespace"
529548
// strategy
530-
None
531549
}
532-
});
550+
}
533551

534-
self_type.unwrap_or_else(|| {
535-
namespace::item_namespace(
536-
cx,
537-
DefId {
538-
krate: instance.def_id().krate,
539-
index: cx
540-
.tcx
541-
.def_key(instance.def_id())
542-
.parent
543-
.expect("get_containing_scope: missing parent?"),
544-
},
545-
)
546-
})
552+
let scope = namespace::item_namespace(
553+
cx,
554+
DefId {
555+
krate: instance.def_id().krate,
556+
index: cx
557+
.tcx
558+
.def_key(instance.def_id())
559+
.parent
560+
.expect("get_containing_scope: missing parent?"),
561+
},
562+
);
563+
(scope, false)
547564
}
548565
}
549566

‎compiler/rustc_codegen_llvm/src/llvm/ffi.rs

+15
Original file line numberDiff line numberDiff line change
@@ -1987,6 +1987,21 @@ extern "C" {
19871987
Decl: Option<&'a DIDescriptor>,
19881988
) -> &'a DISubprogram;
19891989

1990+
pub fn LLVMRustDIBuilderCreateMethod<'a>(
1991+
Builder: &DIBuilder<'a>,
1992+
Scope: &'a DIDescriptor,
1993+
Name: *const c_char,
1994+
NameLen: size_t,
1995+
LinkageName: *const c_char,
1996+
LinkageNameLen: size_t,
1997+
File: &'a DIFile,
1998+
LineNo: c_uint,
1999+
Ty: &'a DIType,
2000+
Flags: DIFlags,
2001+
SPFlags: DISPFlags,
2002+
TParam: &'a DIArray,
2003+
) -> &'a DISubprogram;
2004+
19902005
pub fn LLVMRustDIBuilderCreateBasicType<'a>(
19912006
Builder: &DIBuilder<'a>,
19922007
Name: *const c_char,

‎compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

+22
Original file line numberDiff line numberDiff line change
@@ -831,6 +831,28 @@ extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateFunction(
831831
return wrap(Sub);
832832
}
833833

834+
extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateMethod(
835+
LLVMRustDIBuilderRef Builder, LLVMMetadataRef Scope,
836+
const char *Name, size_t NameLen,
837+
const char *LinkageName, size_t LinkageNameLen,
838+
LLVMMetadataRef File, unsigned LineNo,
839+
LLVMMetadataRef Ty, LLVMRustDIFlags Flags,
840+
LLVMRustDISPFlags SPFlags, LLVMMetadataRef TParam) {
841+
DITemplateParameterArray TParams =
842+
DITemplateParameterArray(unwrap<MDTuple>(TParam));
843+
DISubprogram::DISPFlags llvmSPFlags = fromRust(SPFlags);
844+
DINode::DIFlags llvmFlags = fromRust(Flags);
845+
DISubprogram *Sub = Builder->createMethod(
846+
unwrapDI<DIScope>(Scope),
847+
StringRef(Name, NameLen),
848+
StringRef(LinkageName, LinkageNameLen),
849+
unwrapDI<DIFile>(File), LineNo,
850+
unwrapDI<DISubroutineType>(Ty),
851+
0, 0, nullptr, // VTable params aren't used
852+
llvmFlags, llvmSPFlags, TParams);
853+
return wrap(Sub);
854+
}
855+
834856
extern "C" LLVMMetadataRef LLVMRustDIBuilderCreateBasicType(
835857
LLVMRustDIBuilderRef Builder, const char *Name, size_t NameLen,
836858
uint64_t SizeInBits, unsigned Encoding) {

‎tests/run-make/issue-109934-lto-debuginfo/Makefile

+12
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,12 @@
1+
# ignore-cross-compile
2+
include ../tools.mk
3+
4+
# With the upgrade to LLVM 16, this was getting:
5+
#
6+
# error: Cannot represent a difference across sections
7+
#
8+
# The error stemmed from DI function definitions under type scopes, fixed by
9+
# only declaring in type scope and defining the subprogram elsewhere.
10+
11+
all:
12+
$(RUSTC) lib.rs --test -C lto=fat -C debuginfo=2 -C incremental=$(TMPDIR)/inc-fat

‎tests/run-make/issue-109934-lto-debuginfo/lib.rs

+9
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,9 @@
1+
extern crate alloc;
2+
3+
#[cfg(test)]
4+
mod tests {
5+
#[test]
6+
fn something_alloc() {
7+
assert_eq!(Vec::<u32>::new(), Vec::<u32>::new());
8+
}
9+
}

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