[gcc r14-9538] LoongArch: Fix C23 (...) functions returning large aggregates [PR114175]

[gcc r14-9538] LoongArch: Fix C23 (...) functions returning large aggregates [PR114175]

[Xi Ruoyao]

https://gcc.gnu.org/g:c1fd4589c2bf9fd8409d51b94df219cb75107762

commit r14-9538-gc1fd4589c2bf9fd8409d51b94df219cb75107762
Author: Xi Ruoyao <xry111@xry111.site>
Date:   Mon Mar 18 17:18:34 2024 +0800

    LoongArch: Fix C23 (...) functions returning large aggregates [PR114175]
    
    We were assuming TYPE_NO_NAMED_ARGS_STDARG_P don't have any named
    arguments and there is nothing to advance, but that is not the case
    for (...) functions returning by hidden reference which have one such
    artificial argument.  This is causing gcc.dg/c23-stdarg-6.c and
    gcc.dg/c23-stdarg-8.c to fail.
    
    Fix the issue by checking if arg.type is NULL, as r14-9503 explains.
    
    gcc/ChangeLog:
    
            PR target/114175
            * config/loongarch/loongarch.cc
            (loongarch_setup_incoming_varargs): Only skip
            loongarch_function_arg_advance for TYPE_NO_NAMED_ARGS_STDARG_P
            functions if arg.type is NULL.

Diff:
---
 gcc/config/loongarch/loongarch.cc | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index 70e31bb831c..5344f2a6987 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -767,7 +767,13 @@ loongarch_setup_incoming_varargs (cumulative_args_t cum,
      argument.  Advance a local copy of CUM past the last "real" named
      argument, to find out how many registers are left over.  */
   local_cum = *get_cumulative_args (cum);
-  if (!TYPE_NO_NAMED_ARGS_STDARG_P (TREE_TYPE (current_function_decl)))
+
+  /* For a C23 variadic function w/o any named argument, and w/o an
+     artifical argument for large return value, skip advancing args.
+     There is such an artifical argument iff. arg.type is non-NULL
+     (PR 114175).  */
+  if (!TYPE_NO_NAMED_ARGS_STDARG_P (TREE_TYPE (current_function_decl))
+      || arg.type != NULL_TREE)
     loongarch_function_arg_advance (pack_cumulative_args (&local_cum), arg);
 
   /* Found out how many registers we need to save.  */