debuginfo: no type metadata if substs reqd

This commit skips generating debuginfo type metadata if substitutions
are required by the type. This avoids ICEs that result from layouts
of types with substitutions being computed.

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

Author: davidtwco

src/librustc_codegen_llvm/debuginfo/mod.rs

@@ -26,7 +26,7 @@ use rustc_index::vec::IndexVec;
 use rustc_middle::mir;
 use rustc_middle::ty::layout::HasTyCtxt;
 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
-use rustc_middle::ty::{self, Instance, ParamEnv, Ty};
+use rustc_middle::ty::{self, Instance, ParamEnv, Ty, TypeFoldable};
 use rustc_session::config::{self, DebugInfo};
 use rustc_span::symbol::Symbol;
 use rustc_span::{self, BytePos, Span};
@@ -470,7 +470,9 @@ impl DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
                     match impl_self_ty.kind {
                         ty::Adt(def, ..) if !def.is_box() => {
                             // Again, only create type information if full debuginfo is enabled
-                            if cx.sess().opts.debuginfo == DebugInfo::Full {
+                            if cx.sess().opts.debuginfo == DebugInfo::Full
+                                && !impl_self_ty.needs_subst()
+                            {
                                 Some(type_metadata(cx, impl_self_ty, rustc_span::DUMMY_SP))
                             } else {
                                 Some(namespace::item_namespace(cx, def.did))