function: Fix another TYPE_NO_NAMED_ARGS_STDARG_P spot

When looking at PR114175 (although that bug seems to be now a riscv backend
bug), I've noticed that for the TYPE_NO_NAMED_ARGS_STDARG_P functions which
return value through hidden reference, like
  #include <stdarg.h>

  struct S { char a[64]; };
  int n;

  struct S
  foo (...)
  {
    struct S s = {};
    va_list ap;
    va_start (ap);
    for (int i = 0; i < n; ++i)
      if ((i & 1))
        s.a[0] += va_arg (ap, double);
      else
        s.a[0] += va_arg (ap, int);
    va_end (ap);
    return s;
  }
we were incorrectly calling assign_parms_setup_varargs twice, once
at the start of the function and once in
      if (cfun->stdarg && !DECL_CHAIN (parm))
        assign_parms_setup_varargs (&all, &data, false);
where parm is the last and only "named" parameter.

The first call, guarded with TYPE_NO_NAMED_ARGS_STDARG_P, was added in
r13-3549 and is needed for int bar (...) etc. functions using
va_start/va_arg/va_end, otherwise the
  FOR_EACH_VEC_ELT (fnargs, i, parm)
in which the other call is will not iterate at all.  But we shouldn't
be doing that if we have the hidden return pointer.

With the following patch on the above testcase with -O0 -std=c23 the
assembly difference is:
 	pushq	%rbp
 	.cfi_def_cfa_offset 16
 	.cfi_offset 6, -16
 	movq	%rsp, %rbp
 	.cfi_def_cfa_register 6
 	pushq	%rbx
 	subq	$192, %rsp
 	.cfi_offset 3, -24
-	movq	%rdi, -192(%rbp)
-	movq	%rsi, -184(%rbp)
-	movq	%rdx, -176(%rbp)
-	movq	%rcx, -168(%rbp)
-	movq	%r8, -160(%rbp)
-	movq	%r9, -152(%rbp)
-	testb	%al, %al
-	je	.L2
-	movaps	%xmm0, -144(%rbp)
-	movaps	%xmm1, -128(%rbp)
-	movaps	%xmm2, -112(%rbp)
-	movaps	%xmm3, -96(%rbp)
-	movaps	%xmm4, -80(%rbp)
-	movaps	%xmm5, -64(%rbp)
-	movaps	%xmm6, -48(%rbp)
-	movaps	%xmm7, -32(%rbp)
-.L2:
 	movq	%rdi, -312(%rbp)
 	movq	%rdi, -192(%rbp)
 	movq	%rsi, -184(%rbp)
 	movq	%rdx, -176(%rbp)
 	movq	%rcx, -168(%rbp)
 	movq	%r8, -160(%rbp)
 	movq	%r9, -152(%rbp)
 	testb	%al, %al
-	je	.L13
+	je	.L12
 	movaps	%xmm0, -144(%rbp)
 	movaps	%xmm1, -128(%rbp)
 	movaps	%xmm2, -112(%rbp)
 	movaps	%xmm3, -96(%rbp)
 	movaps	%xmm4, -80(%rbp)
 	movaps	%xmm5, -64(%rbp)
 	movaps	%xmm6, -48(%rbp)
 	movaps	%xmm7, -32(%rbp)
-.L13:
+.L12:
plus some renumbering of labels later on which clearly shows
that because of this bug, we were saving all the registers twice
rather then once.  With -O2 -std=c23 some of it is DCEd, but we still get
 	subq	$160, %rsp
 	.cfi_def_cfa_offset 168
-	testb	%al, %al
-	je	.L2
-	movaps	%xmm0, 24(%rsp)
-	movaps	%xmm1, 40(%rsp)
-	movaps	%xmm2, 56(%rsp)
-	movaps	%xmm3, 72(%rsp)
-	movaps	%xmm4, 88(%rsp)
-	movaps	%xmm5, 104(%rsp)
-	movaps	%xmm6, 120(%rsp)
-	movaps	%xmm7, 136(%rsp)
-.L2:
 	movq	%rdi, -24(%rsp)
 	movq	%rsi, -16(%rsp)
 	movq	%rdx, -8(%rsp)
 	movq	%rcx, (%rsp)
 	movq	%r8, 8(%rsp)
 	movq	%r9, 16(%rsp)
 	testb	%al, %al
-	je	.L13
+	je	.L12
 	movaps	%xmm0, 24(%rsp)
 	movaps	%xmm1, 40(%rsp)
 	movaps	%xmm2, 56(%rsp)
 	movaps	%xmm3, 72(%rsp)
 	movaps	%xmm4, 88(%rsp)
 	movaps	%xmm5, 104(%rsp)
 	movaps	%xmm6, 120(%rsp)
 	movaps	%xmm7, 136(%rsp)
-.L13:
+.L12:
difference, i.e. this time not all, but the floating point args
were conditionally all saved twice.

2024-03-01  Jakub Jelinek  <jakub@redhat.com>

	* function.cc (assign_parms): Only call assign_parms_setup_varargs
	early for TYPE_NO_NAMED_ARGS_STDARG_P functions if fnargs is empty.

1 files changed, 2 insertions, 1 deletions

diff --git a/gcc/function.cc b/gcc/function.cc
index 9488181cbd9..3cef6c17bce 100644
--- a/gcc/function.cc
+++ b/gcc/function.cc
@@ -3650,7 +3650,8 @@ assign_parms (tree fndecl)
   assign_parms_initialize_all (&all);
   fnargs = assign_parms_augmented_arg_list (&all);
 
-  if (TYPE_NO_NAMED_ARGS_STDARG_P (TREE_TYPE (fndecl)))
+  if (TYPE_NO_NAMED_ARGS_STDARG_P (TREE_TYPE (fndecl))
+      && fnargs.is_empty ())
     {
       struct assign_parm_data_one data = {};
       assign_parms_setup_varargs (&all, &data, false);