[gcc r13-8526] LoongArch: Fix C23 (...) functions returning large aggregates [PR114175]

[Xi Ruoyao]

https://gcc.gnu.org/g:b73a6a20113ca607cf3073c751698b12aa167881

commit r13-8526-gb73a6a20113ca607cf3073c751698b12aa167881
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.
    
    (cherry picked from commit c1fd4589c2bf9fd8409d51b94df219cb75107762)

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 e78b81cd8fc..d2c26407447 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -760,7 +760,13 @@ 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.  */