[PATCH] ARM/NEON: Improve codegen for long sext/zext operations.

[Pete Couperus]

Hello,

OK, thanks, that helps a lot.  Here is the patch with the cost-model
changes included.
Let me know if it doesn't look right, or if there is anything else
that I should fix.
Thanks!

Pete


On Sat, Mar 16, 2013 at 8:43 AM, Arnold Schwaighofer
<aschwaighofer at apple.com> wrote:
> Yes that sound right. I see for example:
>
> vmovl.s8
> vmovl.s8
> vmovl.s16
> vmovl.s16
> vmovl.s16
> vmovl.s16
>
> for
>
> %r = sext <16 x i8> %v0 to <16 x i32>
>
>
> That would entail an entry of:
>
>  { ISD::SIGN_EXTEND, MVT::v16i32, MVT::v16i8,  6 },
>
>
> On Mar 16, 2013, at 9:28 AM, Renato Golin <renato.golin at linaro.org> wrote:
>
>> On 16 March 2013 02:51, Pete Couperus <pjcoup at gmail.com> wrote:
>> Thanks for the review.  I'd be happy to modify the cost values.
>> Is there a guideline for what this should be?  I surmise looking at
>> the comments and the other entries that this isn't quite as simple as
>> something like the number of vmovl's.  Or should I just remove the
>> entries corresponding to the cases covered in the patch?
>>
>> Hi Pete,
>>
>> The costs for the operations you're changing are:
>>
>> +    setOperationAction(ISD::SIGN_EXTEND, MVT::v8i32,  Custom);
>> +    setOperationAction(ISD::ZERO_EXTEND, MVT::v8i32,  Custom);
>> +    setOperationAction(ISD::SIGN_EXTEND, MVT::v16i32, Custom);
>> +    setOperationAction(ISD::ZERO_EXTEND, MVT::v16i32, Custom);
>>
>> They don't have specific entries (AFAICS) in the cost tables, so it ends up just exploding the cost. Fair enough, they were a bunch of strh instructions.
>>
>> What you have to do is to add entries in ARMTargetTransformInfo.cpp -> ARMTTI::getCastInstrCost() like:
>>
>>     { ISD::SIGN_EXTEND, MVT::v16i64, MVT::v16i32, 4 },
>>     { ISD::ZERO_EXTEND, MVT::v16i64, MVT::v16i32, 4 },
>>     { ISD::SIGN_EXTEND, MVT::v8i64, MVT::v8i32, 3 },
>>     { ISD::ZERO_EXTEND, MVT::v8i64, MVT::v8i32, 3 },
>>
>> ---> Arnold, please correct me if I'm wrong <---
>>
>> And the ones you're adding new:
>>
>> +    setOperationAction(ISD::SIGN_EXTEND, MVT::v4i64,  Custom);
>> +    setOperationAction(ISD::ZERO_EXTEND, MVT::v4i64,  Custom);
>> +    setOperationAction(ISD::SIGN_EXTEND, MVT::v8i64,  Custom);
>> +    setOperationAction(ISD::ZERO_EXTEND, MVT::v8i64,  Custom);
>>
>> That need similar entries on the table in ARMTTI taking each instruction as an ideal cost of 1.
>>
>> Format is { ISD, DestType, SourceType, Cost };
>>
>> That should improve some vectorized benchmarks, but I don't expect it to show above the noise level in LNT, so let's look for correctness rather than performance for now.
>>
>> cheers,
>> --renato
>
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