Re: [PATCH: PR target/41705] Enable if conversion for thumb1 by new HAVE_conditional_execution definition

[Carrot Wei <carrot@google.com>]

On Sat, Oct 17, 2009 at 2:01 PM, Ian Lance Taylor <iant@google.com> wrote:
> Carrot Wei <carrot@google.com> writes:
>
>> Current method in genconfig.c is looking for COND_EXEC expression. I've
>> grepped several targets, there are several cases have cond_exec but no
>> define_cond_exec. So use define_cond_exec may change their behavior.
>
> I agree that those targets should not be changed.
>
> Would it be possible for genconfig to simply || together the various
> predicates for the various cond_exec insns?
>
>
>> Can we change the output of genconfig.c to
>>
>> #ifndef HAVE_conditional_execution
>> #define HAVE_conditional_execution 1
>> #endif
>>
>> So we can use customized version of HAVE_conditional_execution defined
>> in the target specific header file if we want. Otherwise genconfig.c will
>> generate one according to the contents of md file.
>
> No, I don't think that is a good idea.  Nothing else in gcc works that
> way, and I see nothing to recommend it.  Don't think "how can I solve
> this problem today for me."  Think "how can I solve this for all time
> for all targets in a way that is easy to maintain."
>
I learned this method from the definition of MAX_INSNS_PER_SPLIT.  :)

>
>>> The quick solution would be to introduce a new target hook and change
>>> every place that checks HAVE_conditional_execution to check that.
>>
>> I'm afraid simply replacing all HAVE_conditional_execution with new target hook
>> may break other targets have HAVE_conditional_execution enabled.
>
> Just make the default value for the target hook return
> HAVE_conditional_execution.
>
This is just what I need.
Thank you, Ian!

Carrot