[LLVMdev] disabling combining load/stores in optimizer.

[Dan Gohman]

On Aug 3, 2009, at 1:20 PM, Alireza.Moshtaghi at microchip.com wrote:
>>
>>> I feel that such optimizations may not result in any gain for PIC16
>>>
>>> as PIC16 does everything on i8.
>>>
>>
>>
>> The legalize pass should turn an i64 store into 8 i8 stores
>>
>> then, which is essentially the same as what an {i32,i32} store
>>
>> would turn into. Is there a problem with this?
>>
>>
>>
>
> We are currently doing this, however I think disabling such
> optimizations is a much better solution.

An LLVM design goal is that backends should be able to outsmart
instcombine when necessary, rather than having instcombine be able
to disable parts of itself in order to avoid foiling the backends.
Practicality sometimes steers elsewhere of course. Please explain
why you think suppressing this particular optimization is better;
it isn't obvious how it would look different in the end.

Dan