[COMMITTED] gccrs: Fix duplicated function generation on higher ranked trait bounds

[Arthur Cohen <arthur.cohen@embecosm.com>]

From: Philip Herron <philip.herron@embecosm.com>

Deuplicate function elimination can fail when we compile helpers during
higher ranked trait bound monomorphization. This because the
TyTy::BaseType info can be lost/reset during the compilation process. This
adds a second mechanism to match based on the manged names which is a bit
more reliable. This patch is required since the query based refactor of
the type system so this issue was likely hidden to to using duplicated type
info for higher ranked trait bounds.

gcc/rust/ChangeLog:

	* backend/rust-compile-context.h: Add new optional `asm_name` string
	argument to `lookup_function_decl`.
	* backend/rust-compile-item.cc (CompileItem::visit): Compute assembly
	name and pass it to `lookup_function_decl` when calling it.

Tested on x86_64-pc-linux-gnu, committed on master.

---
 gcc/rust/backend/rust-compile-context.h | 21 ++++++++++++++++++++-
 gcc/rust/backend/rust-compile-item.cc   | 14 ++++++++------
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/gcc/rust/backend/rust-compile-context.h b/gcc/rust/backend/rust-compile-context.h
index 2d379c2a5fa..49f78e19b20 100644
--- a/gcc/rust/backend/rust-compile-context.h
+++ b/gcc/rust/backend/rust-compile-context.h
@@ -148,7 +148,8 @@ public:
   }
 
   bool lookup_function_decl (HirId id, tree *fn, DefId dId = UNKNOWN_DEFID,
-			     const TyTy::BaseType *ref = nullptr)
+			     const TyTy::BaseType *ref = nullptr,
+			     const std::string &asm_name = std::string ())
   {
     // for for any monomorphized fns
     if (ref != nullptr)
@@ -163,11 +164,29 @@ public:
 	  {
 	    const TyTy::BaseType *r = e.first;
 	    tree f = e.second;
+
 	    if (ref->is_equal (*r))
 	      {
 		*fn = f;
 		return true;
 	      }
+
+	    if (DECL_ASSEMBLER_NAME_SET_P (f) && !asm_name.empty ())
+	      {
+		tree raw = DECL_ASSEMBLER_NAME_RAW (f);
+		const char *rptr = IDENTIFIER_POINTER (raw);
+
+		bool lengths_match_p
+		  = IDENTIFIER_LENGTH (raw) == asm_name.size ();
+		if (lengths_match_p
+		    && strncmp (rptr, asm_name.c_str (),
+				IDENTIFIER_LENGTH (raw))
+			 == 0)
+		  {
+		    *fn = f;
+		    return true;
+		  }
+	      }
 	  }
 	return false;
       }
diff --git a/gcc/rust/backend/rust-compile-item.cc b/gcc/rust/backend/rust-compile-item.cc
index d1cdc3b6698..b2e9b3fbf6d 100644
--- a/gcc/rust/backend/rust-compile-item.cc
+++ b/gcc/rust/backend/rust-compile-item.cc
@@ -134,11 +134,18 @@ CompileItem::visit (HIR::Function &function)
 	}
     }
 
+  const Resolver::CanonicalPath *canonical_path = nullptr;
+  bool ok = ctx->get_mappings ()->lookup_canonical_path (
+    function.get_mappings ().get_nodeid (), &canonical_path);
+  rust_assert (ok);
+
+  const std::string asm_name = ctx->mangle_item (fntype, *canonical_path);
+
   // items can be forward compiled which means we may not need to invoke this
   // code. We might also have already compiled this generic function as well.
   tree lookup = NULL_TREE;
   if (ctx->lookup_function_decl (fntype->get_ty_ref (), &lookup,
-				 fntype->get_id (), fntype))
+				 fntype->get_id (), fntype, asm_name))
     {
       // has this been added to the list then it must be finished
       if (ctx->function_completed (lookup))
@@ -160,11 +167,6 @@ CompileItem::visit (HIR::Function &function)
       fntype->override_context ();
     }
 
-  const Resolver::CanonicalPath *canonical_path = nullptr;
-  bool ok = ctx->get_mappings ()->lookup_canonical_path (
-    function.get_mappings ().get_nodeid (), &canonical_path);
-  rust_assert (ok);
-
   if (function.get_qualifiers ().is_const ())
     ctx->push_const_context ();
 
-- 
2.39.1