[gcc(refs/users/aoliva/heads/testme)] arm: fix c23 0-named-args caller-side stdarg

[Alexandre Oliva]

https://gcc.gnu.org/g:8750df1495ce94dbb1e3eb216969cca6ed715636

commit 8750df1495ce94dbb1e3eb216969cca6ed715636
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Thu Dec 14 03:21:24 2023 -0300

    arm: fix c23 0-named-args caller-side stdarg
    
    On arm-eabi targets, c23 stdarg execution tests that pass arguments to
    (...) functions (without any named argument), the caller passes
    everything on the stack, but the callee expects arguments in
    registers.  My reading of the AAPCS32 suggests that the caller is
    correct, so I've arranged for the caller to pass the first arguments
    in registers to TYPE_NO_NAMED_STDARG_P-typed functions.
    
    The implementation issue in calls.cc is that n_named_args is initially
    set to zero in expand_call, so the test argpos < n_named_args yields
    false for all arguments, and aapcs_layout_arg takes !named as meaning
    stack.
    
    But there's a catch there: on targets in which neither
    strict_argument_naming nor !pretend_outgoing_varargs_named hold,
    n_named_args is bumped up to num_actuals, which covers stdarg
    arguments in pre-c23 cases, but not for TYPE_NO_NAMED_ARGS_STDARG_P.
    
    I'm hesitant to modify the generic ABI-affecting code, so I'm going
    for a more surgical fix for ARM AAPCS only.  I suspect we might want
    yet another targetm predicate to enable the n_named_args overriding
    block to disregard TYPE_NO_NAMED_ARGS_STDARG_P, and allow all actuals
    to be passed as if named.
    
    
    for  gcc/ChangeLog
    
            * config/arm/arm.h (CUMULATIVE_ARGS): Add aapcs_pretend_named.
            * config/arm/arm.cc (arm_init_cumulative_args): Set it for
            aapcs no-named-args stdarg functions.
            (aapcs_layout_arg): Ignore named if aapcs_pretend_named.

Diff:
---
 gcc/config/arm/arm.cc | 9 +++++++--
 gcc/config/arm/arm.h  | 1 +
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/gcc/config/arm/arm.cc b/gcc/config/arm/arm.cc
index 0c0cb14a8a4..625bc8646c6 100644
--- a/gcc/config/arm/arm.cc
+++ b/gcc/config/arm/arm.cc
@@ -7018,8 +7018,11 @@ aapcs_layout_arg (CUMULATIVE_ARGS *pcum, machine_mode mode,
   pcum->aapcs_arg_processed = true;
 
   /* Special case: if named is false then we are handling an incoming
-     anonymous argument which is on the stack.  */
-  if (!named)
+     anonymous argument which is on the stack, unless
+     aapcs_pretend_named, in which case we're dealing with a
+     TYPE_NO_NAMED_ARGS_STDARG_P call and, even if args are !named, we
+     ought to use available registers first.  */
+  if (!named && !pcum->aapcs_pretend_named)
     return;
 
   /* Is this a potential co-processor register candidate?  */
@@ -7140,6 +7143,8 @@ arm_init_cumulative_args (CUMULATIVE_ARGS *pcum, tree fntype,
       pcum->aapcs_arg_processed = false;
       pcum->aapcs_cprc_slot = -1;
       pcum->can_split = true;
+      pcum->aapcs_pretend_named = (fntype
+				   && TYPE_NO_NAMED_ARGS_STDARG_P (fntype));
 
       if (pcum->pcs_variant != ARM_PCS_AAPCS)
 	{
diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index a9c2752c0ea..65d2d567686 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -1702,6 +1702,7 @@ typedef struct
   unsigned aapcs_vfp_reg_alloc;
   int aapcs_vfp_rcount;
   MACHMODE aapcs_vfp_rmode;
+  bool aapcs_pretend_named; /* Set for TYPE_NO_NAMED_ARGS_STDARG_P.  */
 } CUMULATIVE_ARGS;
 #endif