From: Kyrill Tkachov <kyrylo.tkachov@arm.com>
To: Evandro Menezes <e.menezes@samsung.com>,
GCC Patches <gcc-patches@gcc.gnu.org>,
Marcus Shawcroft <Marcus.Shawcroft@arm.com>,
James Greenhalgh <james.greenhalgh@arm.com>,
Andrew Pinski <pinskia@gmail.com>,
Benedikt Huber <benedikt.huber@theobroma-systems.com>,
philipp.tomsich@theobroma-systems.com
Subject: Re: [AArch64] Emit square root using the Newton series
Date: Wed, 09 Dec 2015 17:03:00 -0000 [thread overview]
Message-ID: <56685EBD.5040401@arm.com> (raw)
In-Reply-To: <56685DF2.4040306@samsung.com>
On 09/12/15 16:59, Evandro Menezes wrote:
> On 12/09/2015 10:52 AM, Kyrill Tkachov wrote:
>> Hi Evandro,
>>
>> On 08/12/15 21:35, Evandro Menezes wrote:
>>> Emit square root using the Newton series
>>>
>>> 2015-12-03 Evandro Menezes <e.menezes@samsung.com>
>>>
>>> gcc/
>>> * config/aarch64/aarch64-protos.h (aarch64_emit_swsqrt):
>>> Declare new
>>> function.
>>> * config/aarch64/aarch64-simd.md (sqrt<mode>2): New
>>> expansion and
>>> insn definitions.
>>> * config/aarch64/aarch64-tuning-flags.def
>>> (AARCH64_EXTRA_TUNE_FAST_SQRT): New tuning macro.
>>> * config/aarch64/aarch64.c (aarch64_emit_swsqrt): Define
>>> new function.
>>> * config/aarch64/aarch64.md (sqrt<mode>2): New expansion
>>> and insn
>>> definitions.
>>> * config/aarch64/aarch64.opt (mlow-precision-recip-sqrt):
>>> Expand option
>>> description.
>>> * doc/invoke.texi (mlow-precision-recip-sqrt): Likewise.
>>>
>>> This patch extends the patch that added support for implementing x^-1/2 using the Newton series by adding support for x^1/2 as well.
>>>
>>> Is it OK at this point of stage 3?
>>>
>>
>> A comment on the patch itself from me...
>>
>> diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def b/gcc/config/aarch64/aarch64-tuning-flags.def
>> index 6f7dbce..11c6c9a 100644
>> --- a/gcc/config/aarch64/aarch64-tuning-flags.def
>> +++ b/gcc/config/aarch64/aarch64-tuning-flags.def
>> @@ -30,4 +30,4 @@
>>
>> AARCH64_EXTRA_TUNING_OPTION ("rename_fma_regs", RENAME_FMA_REGS)
>> AARCH64_EXTRA_TUNING_OPTION ("recip_sqrt", RECIP_SQRT)
>> -
>> +AARCH64_EXTRA_TUNING_OPTION ("fast_sqrt", FAST_SQRT)
>>
>> That seems like a misleading name to me.
>> If we're doing this, that means that the sqrt instruction is not faster
>> than doing the inverse sqrt estimation followed by a multiply.
>> I think a name like "synth_sqrt" or "estimate_sqrt" or something along those lines
>> is more appropriate.
>
> Unfortunately, this is the case on Exynos M1: the series is faster than the instruction. :-( So, other targets when this is also true, using the "fast_sqrt" option might make sense.
>
Sure, but the way your patch is written, we will emit the series when "fast_sqrt" is set, rather
than the other way around, unless I'm misreading the logic in:
diff --git a/gcc/config/aarch64/aarch64-simd.md b/gcc/config/aarch64/aarch64-simd.md
index 030a101..f6d2da4 100644
--- a/gcc/config/aarch64/aarch64-simd.md
+++ b/gcc/config/aarch64/aarch64-simd.md
@@ -4280,7 +4280,23 @@
;; sqrt
-(define_insn "sqrt<mode>2"
+(define_expand "sqrt<mode>2"
+ [(set (match_operand:VDQF 0 "register_operand")
+ (sqrt:VDQF (match_operand:VDQF 1 "register_operand")))]
+ "TARGET_SIMD"
+{
+ if ((AARCH64_EXTRA_TUNE_FAST_SQRT & aarch64_tune_params.extra_tuning_flags)
+ && !optimize_function_for_size_p (cfun)
+ && flag_finite_math_only
+ && !flag_trapping_math
+ && flag_unsafe_math_optimizations)
+ {
+ aarch64_emit_swsqrt (operands[0], operands[1]);
+ DONE;
+ }
+})
Thanks,
Kyrill
next prev parent reply other threads:[~2015-12-09 17:03 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-08 21:35 Evandro Menezes
2015-12-09 14:05 ` Marcus Shawcroft
2015-12-09 16:31 ` Evandro Menezes
2015-12-09 16:52 ` Kyrill Tkachov
2015-12-09 16:59 ` Evandro Menezes
2015-12-09 17:03 ` Kyrill Tkachov [this message]
2015-12-09 17:16 ` Kyrill Tkachov
2015-12-09 18:50 ` Evandro Menezes
2015-12-10 10:30 ` Kyrill Tkachov
2016-02-23 0:50 ` Evandro Menezes
2016-02-26 15:00 ` James Greenhalgh
2016-02-26 23:42 ` Evandro Menezes
2016-02-26 23:46 ` Evandro Menezes
2016-02-16 20:56 ` Evandro Menezes
2016-03-04 0:22 ` Evandro Menezes
2016-03-08 22:08 ` Evandro Menezes
2016-03-08 22:18 ` Evandro Menezes
2016-03-08 22:20 ` Evandro Menezes
2016-03-16 19:45 ` Evandro Menezes
2016-03-17 14:55 ` James Greenhalgh
2016-03-17 16:25 ` Evandro Menezes
[not found] <AM3PR08MB00886499882773F3C8B9F71D83B30@AM3PR08MB0088.eurprd08.prod.outlook.com>
[not found] ` <011d01d17a26$31b3ade0$951b09a0$@samsung.com>
2016-03-10 16:52 ` Wilco Dijkstra
2016-03-10 16:58 ` Evandro Menezes
2016-03-10 19:10 ` Wilco Dijkstra
2016-03-10 22:15 ` Evandro Menezes
2016-03-11 1:06 ` Wilco Dijkstra
2016-03-14 16:39 ` Evandro Menezes
2016-03-14 19:13 ` Wilco Dijkstra
2016-03-16 21:44 ` Evandro Menezes
2016-03-17 22:50 Evandro Menezes
2016-03-24 20:30 ` [AArch64] " Evandro Menezes
2016-04-01 22:45 ` Evandro Menezes
2016-04-04 16:32 ` Evandro Menezes
[not found] ` <DB3PR08MB008902F0F0AFA3B1F1C91511839E0@DB3PR08MB0089.eurprd08.prod.outlook.com>
2016-04-05 22:30 ` Evandro Menezes
2016-04-12 18:15 ` Evandro Menezes
2016-04-21 18:44 ` Evandro Menezes
2016-04-27 14:24 ` James Greenhalgh
2016-04-27 15:45 ` Evandro Menezes
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