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Re: question about speculative scheduling in gcc
On Sun, Sep 20, 2009 at 3:43 PM, Maxim Kuvyrkov <maxim@codesourcery.com> wrote:
> Amker.Cheng wrote:
>>
>> Hi :
>> I'm puzzled when looking into speculative scheduling in gcc, the 4.2.4
>> version.
>>
>> First, I noticed the document describing IBM haifa instruction
>> scheduler(as PowerPC Reference Compiler Optimization Project).
>>
>> It presents that the instruction motion from bb s(dominated by t)
>> to t is speculative when split_blocks(s, t) not empty.
>>
>> Second, There is SCED_FLAGS like DO_SPECULATION in codes.
>
> These are two different types of speculative optimizations.
>
>>
>> Here goes questions.
>> 1, Does the DO_SPECULATION flag constrol whether do the
>> ? ?mentioned speculative motion or not?
>
> DO_SPECULATION flag controls generation of IA64 data and control speculative
> instructions. ?It is not used on other architectures.
>
> Speculative instruction moves from the split blocks are controlled by
> flag_schedule_speculative.
>
> --
> Maxim
>
Yes! I've just found it's used for IA64 and was merged into gcc in
version 4.2.0.
Thanks.
--
Best Regards.