Re: [PATCH 0/3] [APX CFCMOV] Support APX CFCMOV

[Jeff Law <jeffreyalaw@gmail.com>]

On 6/14/24 11:10 AM, Alexander Monakov wrote:
> 
> On Fri, 14 Jun 2024, Kong, Lingling wrote:
> 
>> APX CFCMOV[1] feature implements conditionally faulting which means that all memory faults are suppressed
>> when the condition code evaluates to false and load or store a memory operand. Now we could load or store a
>> memory operand may trap or fault for conditional move.
>>
>> In middle-end, now we don't support a conditional move if we knew that a load
>> from A or B could trap or fault.
> 
> Predicated loads&stores on Itanium don't trap either. They are modeled via
> COND_EXEC on RTL. The late if-conversion pass (the instance that runs after
> reload) is capable of introducing them.
> 
>> To enable CFCMOV, we add a target HOOK TARGET_HAVE_CONDITIONAL_MOVE_MEM_NOTRAP
>> in if-conversion pass to allow convert to cmov.
> 
> Considering the above, is the new hook really necessary? Can you model the new
> instructions via (cond_exec () (set ...)) instead of (set (if_then_else ...)) ?
Note that turning on cond_exec will turn off some of the cmove support.

But the general suggesting of trying to avoid a hook for this is a good 
one.  In fact, my first reaction to this thread was "do we really need a 
hook for this".

jeff