https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100955
Bug ID: 100955
Summary: varargs causes extra stores to/from stack
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Target: aarch64-linux-gnu
Take:
#include <stdarg.h>
int vfprintf1 (const char *, va_list);
int
__fprintf1 (const char *format, ...)
{
va_list arg;
int done;
va_start (arg, format);
done = vfprintf1 (format, arg);
va_end (arg);
return done;
}
---- CUT ---
Currently at -O2 we produce:
stp x29, x30, [sp, -272]!
mov w9, -56
mov w8, -128
mov x29, sp
add x10, sp, 208
add x11, sp, 272
stp x11, x11, [sp, 48]
str x10, [sp, 64]
stp w9, w8, [sp, 72]
str q0, [sp, 80]
ldp q0, q16, [sp, 48]
str q1, [sp, 96]
str q2, [sp, 112]
stp q0, q16, [sp, 16]
str q3, [sp, 128]
str q4, [sp, 144]
str q5, [sp, 160]
str q6, [sp, 176]
str q7, [sp, 192]
stp x1, x2, [sp, 216]
add x1, sp, 16
stp x3, x4, [sp, 232]
stp x5, x6, [sp, 248]
str x7, [sp, 264]
bl vfprintf1
Notice how we store to arg (va_list) and then do a copy of arg (va_list) to
pass to the vfprintf1.
This is due to
__builtin_va_start (&arg, 0);
If we had arg = __builtin_va_start_internal(); and expanded that instead, there
would be no needed.
