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Re: ifcvt/crossjump patch: Fix PR 42496, 21803

On 04/20/2010 12:05 AM, Eric Botcazou wrote:
> Bernd Schmidt wrote: 
>> Here's the second part.  This one should help most architectures, not
>> just the ones with conditional execution.  I've observed it helps on
>> i686 and arm, with the following being a typical result:
>>  .L18:
>>         ldr     r1, [r2, #4]
>>         cmp     r1, #34
>> -       it      hi
>> -       ldrhi   r3, .L98+12
>> -       bhi     .L28
>>         ldr     r3, .L98+12
>> +       bhi     .L28
>>         ldrb    r2, [r3, #4]    @ zero_extendqisi2
>>         cbz     r2, .L29
>>         ldr     r3, [r3, #8]
> I'm uncomfortable with this patch because I'm not sure it belongs in ifcvt.c.
> Conceptually it's a reversed form of cross jumping so it could be implemented 
> more generally in cfgcleanup.c.  And other transformations should already be 
> able to apply this kind of optimizations.  Do you have testcases?

Here's a new patch.  A testcase is included; as I mentioned before this
triggers quite frequently.  This is PR44374.

I've moved and reused code from dead_or_predicable for a new function
can_move_insns_across.  The tests in dead_or_predicable were still
somewhat ad-hoc, after the patch I believe it's using the exact
necessary and sufficient conditions for moving code.

Bootstrapped and regression tested on i686-linux.  Ok?


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