debuginfo: add type metadata for params

This commit adds type metadata for generic parameters (that arise from
polymorphization). Generic parameter metadata is considered zero-sized
and named after the generic parameter.

Signed-off-by: David Wood <david@davidtw.co>

Author: davidtwco

src/librustc_codegen_llvm/debuginfo/metadata.rs

@@ -700,6 +700,8 @@ pub fn type_metadata(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>, usage_site_span: Sp
             prepare_tuple_metadata(cx, t, &tys, unique_type_id, usage_site_span, NO_SCOPE_METADATA)
                 .finalize(cx)
         }
+        // Type parameters from polymorphized functions.
+        ty::Param(_) => MetadataCreationResult::new(param_type_metadata(cx, t), false),
         _ => bug!("debuginfo: unexpected type in type_metadata: {:?}", t),
     };
 
@@ -955,6 +957,20 @@ fn pointer_type_metadata(
     }
 }
 
+fn param_type_metadata(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>) -> &'ll DIType {
+    debug!("param_type_metadata: {:?}", t);
+    let name = format!("{:?}", t);
+    return unsafe {
+        llvm::LLVMRustDIBuilderCreateBasicType(
+            DIB(cx),
+            name.as_ptr().cast(),
+            name.len(),
+            Size::ZERO.bits(),
+            DW_ATE_unsigned,
+        )
+    };
+}
+
 pub fn compile_unit_metadata(
     tcx: TyCtxt<'_>,
     codegen_unit_name: &str,

src/librustc_codegen_ssa/debuginfo/type_names.rs

@@ -205,14 +205,17 @@ pub fn push_debuginfo_type_name<'tcx>(
                 tcx.def_key(def_id).disambiguated_data.disambiguator
             ));
         }
+        // Type parameters from polymorphized functions.
+        ty::Param(_) => {
+            output.push_str(&format!("{:?}", t));
+        }
         ty::Error(_)
         | ty::Infer(_)
         | ty::Placeholder(..)
         | ty::Projection(..)
         | ty::Bound(..)
         | ty::Opaque(..)
-        | ty::GeneratorWitness(..)
-        | ty::Param(_) => {
+        | ty::GeneratorWitness(..) => {
             bug!(
                 "debuginfo: Trying to create type name for \
                   unexpected type: {:?}",