d: Fix ICE in finish_thunk (PR97644)

Because this what the upstream reference compiler did, thunks for the D
front-end were associated with the class definition, so were forced
code-gen even if the target function was extern.  This has now been
changed so there are now only generated if there is a function
definition, fixing the ICE that occurred in PR 97644, which was caused
by calling expand_thunk() early.

gcc/d/ChangeLog:

	PR d/97644
	* dmd/MERGE: Merge upstream dmd 95044d8e4.
	* d-target.cc (TargetCPP::thunkMangle): New function.
	* decl.cc (finish_thunk): Don't force expand thunks for external
	functions.
	(make_thunk): Emit thunks only if the function has a definition.
	Generate correct mangling for thunks to C++ classes.

gcc/testsuite/ChangeLog:

	* gdc.dg/pr92216.d: Update scan-assember.

1 files changed, 24 insertions, 32 deletions

diff --git a/gcc/d/decl.cc b/gcc/d/decl.cc
index d668715..218f358 100644
--- a/gcc/d/decl.cc
+++ b/gcc/d/decl.cc
@@ -1693,26 +1693,6 @@ finish_thunk (tree thunk, tree function)
 
   if (DECL_ONE_ONLY (function))
     thunk_node->add_to_same_comdat_group (funcn);
-
-  /* Target assemble_mi_thunk doesn't work across section boundaries
-     on many targets, instead force thunk to be expanded in gimple.  */
-  if (DECL_EXTERNAL (function))
-    {
-      /* cgraph::expand_thunk writes over current_function_decl, so if this
-	 could ever be in use by the codegen pass, we want to know about it.  */
-      gcc_assert (current_function_decl == NULL_TREE);
-
-      if (!stdarg_p (TREE_TYPE (thunk)))
-	{
-	  thunk_node->create_edge (funcn, NULL, thunk_node->count);
-	  expand_thunk (thunk_node, false, true);
-	}
-
-      /* Tell the back-end to not bother inlining the function, this is
-	 assumed not to work as it could be referencing symbols outside
-	 of the current compilation unit.  */
-      DECL_UNINLINABLE (function) = 1;
-    }
 }
 
 /* Return a thunk to DECL.  Thunks adjust the incoming `this' pointer by OFFSET.
@@ -1789,12 +1769,11 @@ make_thunk (FuncDeclaration *decl, int offset)
 
   DECL_CONTEXT (thunk) = d_decl_context (decl);
 
-  /* Thunks inherit the public access of the function they are targetting.
-     When the function is outside the current compilation unit however, then the
-     thunk must be kept private to not conflict.  */
-  TREE_PUBLIC (thunk) = TREE_PUBLIC (function) && !DECL_EXTERNAL (function);
-
-  DECL_EXTERNAL (thunk) = 0;
+  /* Thunks inherit the public access of the function they are targeting.
+     Thunks are connected to the definitions of the functions, so thunks are
+     not produced for external functions.  */
+  TREE_PUBLIC (thunk) = TREE_PUBLIC (function);
+  DECL_EXTERNAL (thunk) = DECL_EXTERNAL (function);
 
   /* Thunks are always addressable.  */
   TREE_ADDRESSABLE (thunk) = 1;
@@ -1806,18 +1785,31 @@ make_thunk (FuncDeclaration *decl, int offset)
   DECL_COMDAT (thunk) = DECL_COMDAT (function);
   DECL_WEAK (thunk) = DECL_WEAK (function);
 
-  tree target_name = DECL_ASSEMBLER_NAME (function);
-  unsigned identlen = IDENTIFIER_LENGTH (target_name) + 14;
-  const char *ident = XNEWVEC (const char, identlen);
-  snprintf (CONST_CAST (char *, ident), identlen,
-	    "_DT%u%s", offset, IDENTIFIER_POINTER (target_name));
+  /* When the thunk is for an extern C++ function, let C++ do the thunk
+     generation and just reference the symbol as extern, instead of
+     forcing a D local thunk to be emitted.  */
+  const char *ident;
+
+  if (decl->linkage == LINKcpp)
+    ident = target.cpp.thunkMangle (decl, offset);
+  else
+    {
+      tree target_name = DECL_ASSEMBLER_NAME (function);
+      unsigned identlen = IDENTIFIER_LENGTH (target_name) + 14;
+      ident = XNEWVEC (const char, identlen);
+
+      snprintf (CONST_CAST (char *, ident), identlen,
+		"_DTi%u%s", offset, IDENTIFIER_POINTER (target_name));
+    }
 
   DECL_NAME (thunk) = get_identifier (ident);
   SET_DECL_ASSEMBLER_NAME (thunk, DECL_NAME (thunk));
 
   d_keep (thunk);
+  free (CONST_CAST (char *, ident));
 
-  finish_thunk (thunk, function);
+  if (!DECL_EXTERNAL (function))
+    finish_thunk (thunk, function);
 
   /* Add it to the list of thunks associated with the function.  */
   DECL_LANG_THUNKS (thunk) = NULL_TREE;