diff mbox

[AArch64] Emit square root using the Newton series

Message ID 56685EBD.5040401@arm.com
State New
Headers show

Commit Message

Kyrylo Tkachov Dec. 9, 2015, 5:02 p.m. UTC 
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:

Comments

Kyrylo Tkachov Dec. 9, 2015, 5:16 p.m. UTC | #1 
On 09/12/15 17:02, Kyrill Tkachov wrote:
>
> 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:
>

Sorry, what I meant to say is it would be clearer, IMO, to describe the compiler action that is being taken
(e.g. the rename_fma_regs tuning flag), in this case it's estimating sqrt using a series.

Kyrill

> 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
>
>
Evandro Menezes Dec. 9, 2015, 6:50 p.m. UTC | #2 
On 12/09/2015 11:16 AM, Kyrill Tkachov wrote:
>
> On 09/12/15 17:02, Kyrill Tkachov wrote:
>>
>> 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:
>>
>
> Sorry, what I meant to say is it would be clearer, IMO, to describe 
> the compiler action that is being taken
> (e.g. the rename_fma_regs tuning flag), in this case it's estimating 
> sqrt using a series.
>
> Kyrill
>
>> 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;
>> +    }
>> +})
>>

Kyrill,

How about "approx_sqrt" for, you guessed it, approximate square root?  
The same adjective would perhaps describe "recip_sqrt" better too.

Thanks,
Kyrylo Tkachov Dec. 10, 2015, 10:30 a.m. UTC | #3 
On 09/12/15 18:50, Evandro Menezes wrote:
> On 12/09/2015 11:16 AM, Kyrill Tkachov wrote:
>>
>> On 09/12/15 17:02, Kyrill Tkachov wrote:
>>>
>>> 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:
>>>
>>
>> Sorry, what I meant to say is it would be clearer, IMO, to describe the compiler action that is being taken
>> (e.g. the rename_fma_regs tuning flag), in this case it's estimating sqrt using a series.
>>
>> Kyrill
>>
>>> 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;
>>> +    }
>>> +})
>>>
>
> Kyrill,
>
> How about "approx_sqrt" for, you guessed it, approximate square root?  The same adjective would perhaps describe "recip_sqrt" better too.
>

Sounds good to me.
Sorry for the bikeshedding.

Kyrill

> Thanks,
>
diff mbox

Patch

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