Auto merge of #89597 - michaelwoerister:improve-vtable-debuginfo, r=wesleywiser

Create more accurate debuginfo for vtables.

Before this PR all vtables would have the same name (`"vtable"`) in debuginfo. Now they get an unambiguous name that identifies the implementing type and the trait that is being implemented.

This is only one of several possible improvements:
- This PR describes vtables as arrays of `*const u8` pointers. It would nice to describe them as structs where function pointer is represented by a field with a name indicative of the method it maps to. However, this requires coming up with a naming scheme that avoids clashes between methods with the same name (which is possible if the vtable contains multiple traits).
- The PR does not update the debuginfo we generate for the vtable-pointer field in a fat `dyn` pointer. Right now there does not seem to be an easy way of getting ahold of a vtable-layout without also knowing the concrete self-type of a trait object.

r? `@wesleywiser`

1 files changed, 7 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_ssa/src/traits/debuginfo.rs b/compiler/rustc_codegen_ssa/src/traits/debuginfo.rs
index 3e66d711d2e..e700afc448f 100644
--- a/compiler/rustc_codegen_ssa/src/traits/debuginfo.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/debuginfo.rs
@@ -1,13 +1,18 @@
 use super::BackendTypes;
 use crate::mir::debuginfo::{FunctionDebugContext, VariableKind};
 use rustc_middle::mir;
-use rustc_middle::ty::{Instance, Ty};
+use rustc_middle::ty::{Instance, PolyExistentialTraitRef, Ty};
 use rustc_span::{SourceFile, Span, Symbol};
 use rustc_target::abi::call::FnAbi;
 use rustc_target::abi::Size;
 
 pub trait DebugInfoMethods<'tcx>: BackendTypes {
-    fn create_vtable_metadata(&self, ty: Ty<'tcx>, vtable: Self::Value);
+    fn create_vtable_metadata(
+        &self,
+        ty: Ty<'tcx>,
+        trait_ref: Option<PolyExistentialTraitRef<'tcx>>,
+        vtable: Self::Value,
+    );
 
     /// Creates the function-specific debug context.
     ///