cgraphclones: Don't share DECL_ARGUMENTS between thunk and its artificial thunk [PR108854]

The following testcase ICEs on x86_64-linux with -m32.  The problem is
we create an artificial thunk and because of -fPIC, ia32 and thunk
destination which doesn't bind locally can't use a mi thunk.
The ICE is because during expansion to RTL we see SSA_NAME for a PARM_DECL,
but the PARM_DECL doesn't have DECL_CONTEXT of the current function.
This is because duplicate_thunk_for_node creates a new DECL_ARGUMENTS chain
only if some arguments need modification.

The following patch fixes it by copying the DECL_ARGUMENTS list even if
the arguments can stay as is, to update DECL_CONTEXT on them.  While for
mi thunks it doesn't really matter because we don't use those arguments
in any way, for other thunks it is important.

2023-02-23  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/108854
	* cgraphclones.cc (duplicate_thunk_for_node): If no parameter
	changes are needed, copy at least DECL_ARGUMENTS PARM_DECL
	nodes and adjust their DECL_CONTEXT.

	* g++.dg/opt/pr108854.C: New test.

1 files changed, 11 insertions, 1 deletions

diff --git a/gcc/cgraphclones.cc b/gcc/cgraphclones.cc
index 4a4773e..7c5d3b2 100644
--- a/gcc/cgraphclones.cc
+++ b/gcc/cgraphclones.cc
@@ -218,7 +218,17 @@ duplicate_thunk_for_node (cgraph_node *thunk, cgraph_node *node)
       body_adj.modify_formal_parameters ();
     }
   else
-    new_decl = copy_node (thunk->decl);
+    {
+      new_decl = copy_node (thunk->decl);
+      for (tree *arg = &DECL_ARGUMENTS (new_decl);
+	   *arg; arg = &DECL_CHAIN (*arg))
+	{
+	  tree next = DECL_CHAIN (*arg);
+	  *arg = copy_node (*arg);
+	  DECL_CONTEXT (*arg) = new_decl;
+	  DECL_CHAIN (*arg) = next;
+	}
+    }
 
   gcc_checking_assert (!DECL_STRUCT_FUNCTION (new_decl));
   gcc_checking_assert (!DECL_INITIAL (new_decl));