tree-inline: Fix up multiversioning with vector arguments [PR105554]

tree-inline: Fix up multiversioning with vector arguments [PR105554]

The following testcase ICEs, because we call tree_function_versioning from
old_decl which has target attributes not supporting V4DImode and so
DECL_MODE of DECL_ARGUMENTS is BLKmode, while new_decl supports those.
tree_function_versioning initially copies DECL_RESULT and DECL_ARGUMENTS
from old_decl to new_decl, then calls initialize_cfun to create cfun
and only when the cfun is created it can later actually remap_decl
DECL_RESULT and DECL_ARGUMENTS etc.
The problem is that initialize_cfun -> push_struct_function ->
allocate_struct_function calls relayout_decl on DECL_RESULT and
DECL_ARGUMENTS, which clobbers DECL_MODE of old_decl and we then ICE because
of it.
In particular, allocate_struct_function does:
      if (!abstract_p)
        {
          /* Now that we have activated any function-specific attributes
             that might affect layout, particularly vector modes, relayout
             each of the parameters and the result.  */
          relayout_decl (result);
          for (tree parm = DECL_ARGUMENTS (fndecl); parm;
               parm = DECL_CHAIN (parm))
            relayout_decl (parm);

          /* Similarly relayout the function decl.  */
          targetm.target_option.relayout_function (fndecl);
        }

      if (!abstract_p && aggregate_value_p (result, fndecl))
        {
 #ifdef PCC_STATIC_STRUCT_RETURN
          cfun->returns_pcc_struct = 1;
 #endif
          cfun->returns_struct = 1;
        }
Now, in the case of tree_function_versioning, I believe all that we need
from these is possibly the
targetm.target_option.relayout_function (fndecl);
call (arm only), we will remap DECL_RESULT and DECL_ARGUMENTS later on
and copy_decl_for_dup_finish in that case will handle all we need:
  /* For vector typed decls make sure to update DECL_MODE according
     to the new function context.  */
  if (VECTOR_TYPE_P (TREE_TYPE (copy)))
    SET_DECL_MODE (copy, TYPE_MODE (TREE_TYPE (copy)));
We don't need the cfun->returns_*struct either, because we override it
in initialize_cfun a few lines later:
  /* Copy items we preserve during cloning.  */
...
  cfun->returns_struct = src_cfun->returns_struct;
  cfun->returns_pcc_struct = src_cfun->returns_pcc_struct;

So, to avoid the clobbering of DECL_RESULT/DECL_ARGUMENTS of old_decl,
the following patch arranges allocate_struct_function to be called with
abstract_p true and calls targetm.target_option.relayout_function (fndecl);
by hand.

The removal of DECL_RESULT/DECL_ARGUMENTS copying at the start of
initialize_cfun is removed because the only caller -
tree_function_versioning, does that unconditionally before.

2023-03-17  Jakub Jelinek  <jakub@redhat.com>

	PR target/105554
	* function.h (push_struct_function): Add ABSTRACT_P argument defaulted
	to false.
	* function.cc (push_struct_function): Add ABSTRACT_P argument, pass it
	to allocate_struct_function instead of false.
	* tree-inline.cc (initialize_cfun): Don't copy DECL_ARGUMENTS
	nor DECL_RESULT here.  Pass true as ABSTRACT_P to
	push_struct_function.  Call targetm.target_option.relayout_function
	after it.
	(tree_function_versioning): Formatting fix.

	* gcc.target/i386/pr105554.c: New test.