[llvm-commits] Speeding up instruction selection

[Evan Cheng]

On Apr 23, 2008, at 10:27 AM, Roman Levenstein wrote:

> Hi,
>
> 2008/4/23 Evan Cheng <evan.cheng at apple.com>:
>> Very nice!
>
>> Please run it through MultiSource and SingleSource tests.
> Will do.
>
>> Dan and I  will run it through External tests.
> Very nice.
>
>> If it shows no regression and llvm- gcc bootstrapping works. Then  
>> please check it in.
>
> Just to make it clear:
> This patch is applied currently to the output of Tablegen.
> But the proper patch will need to change the Tablegen to generate
> correct *.inc files.
> Thinking about it, I have a question:
> Right now, the beginning of the generrated instruction selector files
> is always the same, independent of the *.td file and target
> architecture.
> But it is generated by tablegen still and therefore cannot be
> substituted easily, without changing the tablegen.
> Question: May be it is better to define this common part in an include
> file, e.g. ISelHeader.h, and then tablegen would generate only the
> #include <llvm/CodeGen/ISelHeader.h> line. What do you think?

That's a good idea.

Evan

>
>
> -Roman
>
>> On Apr 23, 2008, at 12:35 AM, Roman Levenstein wrote:
>>
>>>
>>>
>>>> In addition to regular testing, since this patch doesn't modify any
>>>> heuristics, it should be possible to compare assembly output
>>>> between an unmodified compiler and one with this patch applied.
>>>> Can you verify that this patch doesn't change any output on some
>>>> interesting testcases?
>>>
>>> I tried it with Kimwitu, which is a very big and complex test-case.
>>> All approaches produce exactly the same assembler code. On my
>>> test-cases with very big BBs it also produces exactly the same
>>> results.
>>>
>>> For the sake of comparison, here are also some time statistics for  
>>> the
>>> compilation of Kimwitu, measured by means of the Linux "time"  
>>> command:
>>>
>>> Current LLVM approach:
>>> real    1m51.464s
>>> user    1m21.161s
>>> sys     0m8.529s
>>>
>>> std::set approach:
>>> real    1m37.938s (13% faster than current LLVM implementation)
>>> user    1m16.169s
>>> sys     0m7.732s
>>>
>>> NO_QUEUE approach:
>>> real    1m29.548s (20% faster than current LLVM implementation)
>>> user    1m14.949s
>>> sys     0m7.824s
>>>
>>>
>>> -Roman
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