https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66013
Bug ID: 66013
Summary: Missed optimization after inlining va_list parameter,
-m32 case
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: trivial
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
Target Milestone: ---
[ -m32 twin PR of PR66010 ]
Consider this test-case (based on gcc.dg/tree-ssa/stdarg-2.c, f15):
...
#include <stdarg.h>
int
f1 (int i, ...)
{
int res;
va_list ap;
va_start (ap, i);
res = va_arg (ap, int);
va_end (ap);
return res;
}
inline int __attribute__((always_inline))
f2_1 (va_list ap)
{
return va_arg (ap, int);
}
int
f2 (int i, ...)
{
int res;
va_list ap;
va_start (ap, i);
res = f2_1 (ap);
va_end (ap);
return res;
}
...
When compiling at -O2 with -m32, the optimized dump for f1 and f2 are very
similar:
...
# .MEM_9 = VDEF <.MEM_1(D)>
# USE = anything
# CLB = anything
- ap_8 = __builtin_next_argD.993 (0);
- ap_6 = ap_8;
+ ap_11 = __builtin_next_argD.993 (0);
+ ap_6 = ap_11;
# PT = nonlocal
- ap_7 = ap_6;
+ ap_3 = ap_6;
# VUSE <.MEM_9>
- res_4 = MEM[(intD.1 *)ap_7];
+ _7 = MEM[(intD.1 *)ap_3];
GIMPLE_NOP
# VUSE <.MEM_9>
- return res_4;
+ return _7;
;; succ: EXIT [100.0%]
...
However, at pass_stdarg, we see on one hand:
...
f1: va_list escapes 0, needs to save 4 GPR units and all FPR units.
...
but OTOH:
...
f2: va_list escapes 1, needs to save all GPR units and all FPR units.
...
Still the .s code is identical for f1 and f2:
...
.cfi_startproc
movl 8(%esp), %eax
ret
.cfi_endproc
...
This is because ix86_setup_incoming_varargs doesn't do anything for -m32:
...
static void
ix86_setup_incoming_varargs (cumulative_args_t cum_v, machine_mode mode,
tree type, int *, int no_rtl)
{
CUMULATIVE_ARGS *cum = get_cumulative_args (cum_v);
CUMULATIVE_ARGS next_cum;
tree fntype;
/* This argument doesn't appear to be used anymore. Which is good,
because the old code here didn't suppress rtl generation. */
gcc_assert (!no_rtl);
if (!TARGET_64BIT)
return;
...
