On 07/08/14 13:57, Kyrill Tkachov wrote:
>
> On 07/08/14 13:46, Richard Earnshaw wrote:
>> On 07/08/14 12:32, Kyrill Tkachov wrote:
>>> On 16/05/14 13:35, Richard Earnshaw wrote:
>>>> On 08/05/14 18:36, Ian Bolton wrote:
>>>>> Hi,
>>>>>
>>>>> It currently takes 4 instructions to generate certain immediates on
>>>>> AArch64 (unless we put them in the constant pool).
>>>>>
>>>>> For example ...
>>>>>
>>>>> long long
>>>>> ffffbeefcafebabe ()
>>>>> {
>>>>> return 0xFFFFBEEFCAFEBABEll;
>>>>> }
>>>>>
>>>>> leads to ...
>>>>>
>>>>> mov x0, 0x47806
>>>>> mov x0, 0xcafe, lsl 16
>>>>> mov x0, 0xbeef, lsl 32
>>>>> orr x0, x0, -281474976710656
>>>>>
>>>>> The above case is tackled in this patch by employing MOVN
>>>>> to generate the top 32-bits in a single instruction ...
>>>>>
>>>>> mov x0, -71536975282177
>>>>> movk x0, 0xcafe, lsl 16
>>>>> movk x0, 0xbabe, lsl 0
>>>>>
>>>>> Note that where at least two half-words are 0xffff, existing
>>>>> code that does the immediate in two instructions is still used.)
>>>>>
>>>>> Tested on standard gcc regressions and the attached test case.
>>>>>
>>>>> OK for commit?
>>>> What about:
>>>>
>>>> long long a()
>>>> {
>>>> return 0x1234ffff56789abcll;
>>>> }
>>>>
>>>> long long b()
>>>> {
>>>> return 0x12345678ffff9abcll;
>>>> }
>>>>
>>>> long long c()
>>>> {
>>>> return 0x123456789abcffffll;
>>>> }
>>>>
>>>> ?
>>>>
>>>> Surely these can also benefit from this sort of optimization, but it
>>>> looks as though you only handle the top 16 bits being set.
>>> Hi Richard,
>>>
>>> How about this rework of the patch?
>>>
>>> For code:
>>>
>>> long long foo ()
>>> {
>>> return 0xFFFFBEEFCAFEBABEll;
>>> }
>>>
>>> long long a()
>>> {
>>> return 0x1234ffff56789abcll;
>>> }
>>>
>>> long long b()
>>> {
>>> return 0x12345678ffff9abcll;
>>> }
>>>
>>> long long c()
>>> {
>>> return 0x123456789abcffffll;
>>> }
>>>
>>> we now generate:
>>> foo:
>>> mov x0, -17730
>>> movk x0, 0xcafe, lsl 16
>>> movk x0, 0xbeef, lsl 32
>>> ret
>>> .size foo, .-foo
>>> .align 2
>>> .global a
>>> .type a, %function
>>> a:
>>> mov x0, -25924
>>> movk x0, 0x5678, lsl 16
>>> movk x0, 0x1234, lsl 48
>>> ret
>>> .size a, .-a
>>> .align 2
>>> .global b
>>> .type b, %function
>>> b:
>>> mov x0, -25924
>>> movk x0, 0x5678, lsl 32
>>> movk x0, 0x1234, lsl 48
>>> ret
>>> .size b, .-b
>>> .align 2
>>> .global c
>>> .type c, %function
>>> c:
>>> mov x0, -1698889729
>>> movk x0, 0x5678, lsl 32
>>> movk x0, 0x1234, lsl 48
>>> ret
>>>
>>>
>>> 3 instructions are used in each case.
>>>
>>> Thanks,
>>> Kyrill
>>>
>>> 2014-08-07 Ian Bolton <[email protected]>
>>> Kyrylo Tkachov <[email protected]>
>>>
>>> * config/aarch64/aarch64.c (aarch64_expand_mov_immediate):
>>> Use MOVN when one of the half-words is 0xffff.
>>>
>>>
>>> aarch64-movn-pattern-patch-v3.patch
>>>
>>>
>>> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
>>> index 0a7f441..2db91c7 100644
>>> --- a/gcc/config/aarch64/aarch64.c
>>> +++ b/gcc/config/aarch64/aarch64.c
>>> @@ -1005,7 +1005,7 @@ aarch64_expand_mov_immediate (rtx dest, rtx imm)
>>> unsigned HOST_WIDE_INT val;
>>> bool subtargets;
>>> rtx subtarget;
>>> - int one_match, zero_match;
>>> + int one_match, zero_match, first_not_ffff_match;
>>>
>>> gcc_assert (mode == SImode || mode == DImode);
>>>
>>> @@ -1106,29 +1106,48 @@ aarch64_expand_mov_immediate (rtx dest, rtx imm)
>>> one_match = 0;
>>> zero_match = 0;
>>> mask = 0xffff;
>>> + first_not_ffff_match = -1;
>>>
>>> for (i = 0; i < 64; i += 16, mask <<= 16)
>>> {
>>> - if ((val & mask) == 0)
>>> - zero_match++;
>>> - else if ((val & mask) == mask)
>>> + if ((val & mask) == mask)
>>> one_match++;
>>> + else
>>> + {
>>> + if (first_not_ffff_match < 0)
>>> + first_not_ffff_match = i;
>>> + if ((val & mask) == 0)
>>> + zero_match++;
>>> + }
>>> }
>>>
>>> if (one_match == 2)
>>> {
>>> - mask = 0xffff;
>>> - for (i = 0; i < 64; i += 16, mask <<= 16)
>>> + /* Set one of the quarters and then insert back into result. */
>>> + mask = 0xffffll << first_not_ffff_match;
>>> + emit_insn (gen_rtx_SET (VOIDmode, dest, GEN_INT (val | mask)));
>>> + emit_insn (gen_insv_immdi (dest, GEN_INT (first_not_ffff_match),
>>> + GEN_INT ((val >> first_not_ffff_match)
>>> + & 0xffff)));
>>> + return;
>>> + }
>>> +
>>> + if (one_match == 1)
>> I think this should be (one_match > zero_match).
>>
>> Otherwise constants such as
>>
>>
>> 0x00001234ffff0000ll
>>
>> might end up taking three rather than two insns.
>
> You're right, we generate:
> mov x0, -65536
> movk x0, 0x1234, lsl 32
> and x0, x0, 281474976710655
>
> with your suggestion we can improve this to:
> mov x0, 4294901760
> movk x0, 0x1234, lsl 32
>
> Ok with that change then?
>
> Kyrill
>
> 2014-08-07 Ian Bolton<[email protected]>
> Kyrylo Tkachov<[email protected]>
>
> * config/aarch64/aarch64.c (aarch64_expand_mov_immediate):
> Use MOVN when one of the half-words is 0xffff.
>
>
OK.
R.
