Fallout: save/restore target options in handle_optimize_attribute

[Martin Liška]

Hi.

There's a fallout after my revision ebd5e86c0f41dc1d692f9b2b68a510b1f6835a3e. I 
would like to analyze
all case and discuss possible solution. To be honest it's a can of worms and 
reverting the commit
is an option on the table.

So the cases:

1) PR100759 - ppc64le

$ cat pr.C
#pragma GCC optimize 0
void main();

$ ./xgcc -B. -Os pr.C
pr.C:2:11: internal compiler error: ‘global_options’ are modified in local 
context
    2 | void main();

What happens: we change from -Os to -O0 and rs6000_isa_flags differ in 
cl_optimization_compare.
Problem is that OPTION_MASK_SAVE_TOC_INDIRECT is set based on optimize flag:

  /* If we can shrink-wrap the TOC register save separately, then use
     -msave-toc-indirect unless explicitly disabled.  */
  if ((rs6000_isa_flags_explicit & OPTION_MASK_SAVE_TOC_INDIRECT) == 0
      && flag_shrink_wrap_separate
      && optimize_function_for_speed_p (cfun))
    rs6000_isa_flags |= OPTION_MASK_SAVE_TOC_INDIRECT;

Suggested solution is doing:

  if ((rs6000_isa_flags_explicit & OPTION_MASK_SAVE_TOC_INDIRECT) == 0
      && flag_shrink_wrap_separate
    rs6000_isa_flags |= OPTION_MASK_SAVE_TOC_INDIRECT;

and add '&& optimize_function_for_speed_p (cfun)' to the place where the option 
mask is used.

2) Joseph's case:

$ cat ~/Programming/testcases/opts-bug.i
extern unsigned long int x;
extern float f (float);
extern __typeof (f) f_power8;
extern __typeof (f) f_power9;
extern __typeof (f) f __attribute__ ((ifunc ("f_ifunc")));
static __attribute__ ((optimize ("-fno-stack-protector"))) __typeof (f) *
f_ifunc (void)
{
  __typeof (f) *res = x ? f_power9 : f_power8;
  return res;
}

$ ./xgcc -B. ~/Programming/testcases/opts-bug.i -c -S -O2 -mlong-double-128 
-mabi=ibmlongdouble
/home/marxin/Programming/testcases/opts-bug.i:8:1: error: ‘-mabi=ibmlongdouble’ 
requires ‘-mlong-double-128’

This is caused by a weird option override:

  else if (rs6000_long_double_type_size == 128)
    rs6000_long_double_type_size = FLOAT_PRECISION_TFmode; (it's 127)

later when rs6000_option_override_internal is called for saved target flags 
(127), it complains.
Possible fix:

  else if (rs6000_long_double_type_size == 128
           || rs6000_long_double_type_size == FLOAT_PRECISION_TFmode)

3) ARM issue reported here:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98636#c20

  arm_fp16_inst = bitmap_bit_p (arm_active_target.isa, isa_bit_fp16);
  if (arm_fp16_inst)
    {
      if (arm_fp16_format == ARM_FP16_FORMAT_ALTERNATIVE)
        error ("selected fp16 options are incompatible");
      arm_fp16_format = ARM_FP16_FORMAT_IEEE;
    }

there's likely missing else branch which would reset when arm_fp16_inst is null.
Anyway, can be moved again to the ignored list

4) Jeff reported the following for v850-elf:

$ cat ~/Programming/testcases/j.c
typedef __SIZE_TYPE__ size_t;

extern inline __attribute__ ((__always_inline__, __gnu_inline__, 
__artificial__, __nothrow__, __leaf__)) void *
memcpy (void *__restrict __dest, const void *__restrict __src, size_t __len)
{
  return __builtin___memcpy_chk (__dest, __src, __len, __builtin_object_size 
(__dest, 0));
}

__attribute__((optimize ("Ofast"))) void
bar (void *d, void *s, size_t l)
{
  memcpy (d, s, l);
}

$ ./xgcc -B. ~/Programming/testcases/j.c  -S
/home/marxin/Programming/testcases/j.c: In function ‘bar’:
/home/marxin/Programming/testcases/j.c:4:1: error: inlining failed in call to 
‘always_inline’ ‘memcpy’: target specific option mismatch
    4 | memcpy (void *__restrict __dest, const void *__restrict __src, size_t 
__len)
      | ^~~~~~
/home/marxin/Programming/testcases/j.c:12:3: note: called from here
   12 |   memcpy (d, s, l);
      |   ^~~~~~~~~~~~~~~~

This one is pretty clear. The target does:

    { OPT_LEVELS_1_PLUS, OPT_mprolog_function, NULL, 1 },

So it sets a target option based on optimize level.
This one will need:

diff --git a/gcc/config/v850/v850.c b/gcc/config/v850/v850.c
index e0e5005d865..49f91f12766 100644
--- a/gcc/config/v850/v850.c
+++ b/gcc/config/v850/v850.c
@@ -3140,6 +3140,11 @@ v850_option_override (void)
   /* The RH850 ABI does not (currently) support the use of the CALLT 
instruction.  */
   if (! TARGET_GCC_ABI)
     target_flags |= MASK_DISABLE_CALLT;
+
+  /* Save the initial options in case the user does function specific
+     options.  */
+  target_option_default_node = target_option_current_node
+    = build_target_option_node (&global_options, &global_options_set);
 }

plus a custom can_inline_p target hook where the MASK_PROLOG_FUNCTION is 
ignored because
caller does not have it set, while callee has.

What target maintainers thing about it?

Martin