Hello!
Vzeroupper placement patch uses MODE_EXIT to determine if vzeroupper
has to be placed before function exit. However, when compiling
following test
--cut here--
typedef struct objc_class *Class;
typedef struct objc_object
{
Class class_pointer;
} *id;
typedef const struct objc_selector *SEL;
typedef void * retval_t;
typedef void * arglist_t;
extern retval_t __objc_forward (id object, SEL sel, arglist_t args);
double
__objc_double_forward (id rcv, SEL op, ...)
{
void *args, *res;
args = __builtin_apply_args ();
res = __objc_forward (rcv, op, args);
__builtin_return (res);
}
--cut here--
__builtin_return emits a sequence of loads from "argument area" to all
possible function return registers in their widest mode (together with
corresponding USE RTXes), creating:
(insn 31 30 33 2 (set (reg:DI 0 ax)
(mem:DI (reg/v/f:DI 60 [ res ]) [0 S8 A8])) avx-vzeroupper-27.c:23 -1
(nil))
(insn 33 31 35 2 (set (reg:XF 8 st)
(mem:XF (plus:DI (reg/v/f:DI 60 [ res ])
(const_int 16 [0x10])) [0 S16 A8])) avx-vzeroupper-27.c:23 -1
(nil))
(insn 35 33 32 2 (set (reg:OI 21 xmm0)
(mem:OI (plus:DI (reg/v/f:DI 60 [ res ])
(const_int 32 [0x20])) [0 S32 A8])) avx-vzeroupper-27.c:23 -1
(nil))
(insn 32 35 34 2 (use (reg:DI 0 ax)) avx-vzeroupper-27.c:23 -1
(nil))
(insn 34 32 36 2 (use (reg:XF 8 st)) avx-vzeroupper-27.c:23 -1
(nil))
(insn 36 34 44 2 (use (reg:OI 21 xmm0)) avx-vzeroupper-27.c:23 -1
(nil))
This sequence breaks assumption in mode-switching.c, that final
function return register load operates in MODE_EXIT mode and triggere
following code:
for (j = n_entities - 1; j >= 0; j--)
{
int e = entity_map[j];
int mode = MODE_NEEDED (e, return_copy);
if (mode != num_modes[e] && mode != MODE_EXIT (e))
break;
}
As discussed above, modes of loads, generated from __builtin_apply
have no connection to function return mode. mode-switching.c does
detect __builtin_apply situation and raises maybe_builtin_apply flag,
but doesn't use it to short-circuit wrong check. In proposed patch, we
detect this situation and raise force_late_switch in the same way, as
SH4 does for its "late" fpscr emission. For the testcase above,
following RTX sequence is generated:
(insn 31 30 33 2 (set (reg:DI 0 ax)
(mem:DI (reg/v/f:DI 60 [ res ]) [0 S8 A8]))
avx-vzeroupper-27.c:23 63 {*movdi_internal_rex64}
(nil))
(insn 33 31 35 2 (set (reg:XF 8 st)
(mem:XF (plus:DI (reg/v/f:DI 60 [ res ])
(const_int 16 [0x10])) [0 S16 A8]))
avx-vzeroupper-27.c:23 106 {*movxf_internal}
(nil))
(insn 35 33 52 2 (set (reg:OI 21 xmm0)
(mem:OI (plus:DI (reg/v/f:DI 60 [ res ])
(const_int 32 [0x20])) [0 S32 A8]))
avx-vzeroupper-27.c:23 60 {*movoi_internal_avx}
(expr_list:REG_DEAD (reg/v/f:DI 60 [ res ])
(nil)))
(insn 52 35 49 2 (unspec_volatile [
(const_int 9 [0x9])
] UNSPECV_VZEROUPPER) -1
(nil))
(note 49 52 32 2 NOTE_INSN_DELETED)
(insn 32 49 34 2 (use (reg:DI 0 ax)) avx-vzeroupper-27.c:23 -1
(expr_list:REG_DEAD (reg:DI 0 ax)
(nil)))
(insn 34 32 36 2 (use (reg:XF 8 st)) avx-vzeroupper-27.c:23 -1
(expr_list:REG_DEAD (reg:XF 8 st)
(nil)))
(insn 36 34 44 2 (use (reg:OI 21 xmm0)) avx-vzeroupper-27.c:23 -1
(nil))
(insn 44 36 0 2 (use (reg/i:DF 21 xmm0)) avx-vzeroupper-27.c:24 -1
where mode switching correctly placed vzeroupper insn, based on
MODE_EXIT mode, determined from final use in (insn 44).
2012-11-04 Vladimir Yakovlev <[email protected]>
Uros Bizjak <[email protected]>
* mode-switching.c (create_pre_exit): Added code for
maybe_builtin_apply case.
Patch was bootstrapped and regression tested on x86_64-pc-linux-gnu,
with vzeroupper patch [1] applied.
I have added SH4 maintainer for possible comments.
OK for mainline SVN?
[1] http://gcc.gnu.org/ml/gcc-patches/2012-11/msg00292.html
Uros.
--
Index: mode-switching.c
===================================================================
--- mode-switching.c (revision 193133)
+++ mode-switching.c (working copy)
@@ -342,6 +342,16 @@ create_pre_exit (int n_entities, int *entity_map,
}
if (j >= 0)
{
+ /* __builtin_return emits a sequence of loads to all
+ function value registers in their widest mode,
+ which breaks the assumption on the mode of the
+ return register load. Allow this situation, so the
+ final mode switch will be emitted after the load. */
+ if (maybe_builtin_apply
+ && targetm.calls.function_value_regno_p
+ (copy_start))
+ forced_late_switch = 1;
+
/* For the SH4, floating point loads depend on fpscr,
thus we might need to put the final mode switch
after the return value copy. That is still OK,
