On Mon, Aug 3, 2015 at 3:02 PM, Kyrill Tkachov <[email protected]> wrote:
>
> On 03/08/15 13:33, Uros Bizjak wrote:
>>
>> Hello!
>>
>>> 2015-07-30 Kyrylo Tkachov <[email protected]>
>>>
>>> * ifcvt.c (noce_try_store_flag_constants): Make logic of the case
>>> when diff == STORE_FLAG_VALUE or diff == -STORE_FLAG_VALUE more
>>> explicit. Prefer to add the flag whenever possible.
>>> (noce_process_if_block): Try noce_try_store_flag_constants before
>>> noce_try_cmove.
>>>
>>> 2015-07-30 Kyrylo Tkachov <[email protected]>
>>>
>>> * gcc.target/aarch64/csel_bfx_1.c: New test.
>>> * gcc.target/aarch64/csel_imms_inc_1.c: Likewise.
>>
>> This patch regressed following tests on x86_64:
>>
>> FAIL: gcc.target/i386/cmov2.c scan-assembler sbb
>> FAIL: gcc.target/i386/cmov3.c scan-assembler cmov[^3]
>
>
> Sorry for that :(
> I could have sworn they passed for me during my run...
>
>> While cmov3 case is questionable by itself in light of PR56309 [1],
>> the cnov2 case regressed from:
>>
>> cmpl %edi, %esi
>> sbbl %eax, %eax
>> andl $-10, %eax
>> addl $5, %eax
>> ret
>>
>> to:
>>
>> xorl %eax, %eax
>> cmpl %esi, %edi
>> setbe %al
>> negl %eax
>> andl $10, %eax
>> subl $5, %eax
>> ret
>>
>> Please note that sbb (aka {*x86_movsicc_0_m1} ) is not generated
>> anymore. Non-QImode setcc instructions are problematic on x86, since
>> they need to be zero-extended to their full length.
IMO, we can check if the target is able to generate insn that
implements conditional move between 0 and -1 for certain comparison
mode, like:
#(insn:TI 27 26 28 2 (parallel [
# (set (reg:SI 0 ax [orig:87 D.1845 ] [87])
# (if_then_else:SI (ltu:SI (reg:CC 17 flags)
# (const_int 0 [0]))
# (const_int -1 [0xffffffffffffffff])
# (const_int 0 [0])))
# (clobber (reg:CC 17 flags))
# ]) cmov2.c:9 947 {*x86_movsicc_0_m1}
# (expr_list:REG_DEAD (reg:CC 17 flags)
# (expr_list:REG_UNUSED (reg:CC 17 flags)
# (nil))))
sbbl %eax, %eax # 27 *x86_movsicc_0_m1 [length = 2]
this is the key insn, and as shown above, further asm sequence is
similar between patched and unpatched compiler.
Uros.
