[llvm-commits] [PATCH] TableGen: reduce the size of ContextDecision tables in X86GenDisassemblerTables

[Craig Topper]

I don't follow how you would merge modrm_type and instructionIDs as those
fields are in different tables.

On Mon, Sep 10, 2012 at 7:12 PM, Manman Ren <mren at apple.com> wrote:

>
> Yes, I noticed that the max value is 43459 after I spent the effort to add
> an encoder :(
> But we can potentially combine the modrm_type with instructionIDs to fit
> into a single 16-bit number, thus saving 8-bit for each entry.
>
> Let me know whether that is worth a try.
>
> I will look into how to uniquely the ModRM decision table if possible. Do
> you have specific suggestion on how to?
>
> Thanks,
> Manman
>
> On Sep 10, 2012, at 7:09 PM, Craig Topper <craig.topper at gmail.com> wrote:
>
> Far as I can tell there's no reason you can't just change the existing
> index to 16-bits. The largest index is 43459. I'd rather to see effort
> spent uniquifying the ModRM decision table which will provide a much larger
> bang.
>
> On Mon, Sep 10, 2012 at 12:28 PM, Manman Ren <mren at apple.com> wrote:
>
>>
>> TableGen: reduce the size of ContextDecision tables in
>> X86GenDisassemblerTables
>> by adding an encoder for instructionIDs. The main motivation is that in
>> 83% of
>> the cases, the value is zero, so we should be able to use a 16-bit index
>> into the encoder and the encoder will translate the index into the actual
>> 32-bit value.
>>
>> Later on, we may combine the modrm_type with instructionIDs to fit into a
>> single
>> 16-bit number.
>>
>> The size of libLTO in a Release build is reduced by 200k. The downside is
>> one
>> more memory access to the encoder when decoding the instruction ID.
>>
>> Thanks for reviewing the patch! Comments are greatly appreciated.
>>
>> Manman
>>
>>
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>>
>>
>
>
> --
> ~Craig
>
>
>


-- 
~Craig
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