[LLVMdev] Stop MachineCSE on certain instructions

[girish gulawani]

Hi Evan.
The hasSideEffects method I believe operates only on Inline Assembly (IA) blocks. What if such a sequence is not part of IA?


Thanks.
Girish.

If an instruction is marked as side-effect free then it's a candidate for CSE. Try marking the instruction with hasSideEffects.
>
>Evan
>
>On Dec 17, 2011, at 12:24 PM, Johannes Birgmeier wrote:
>
>> Hello,
>> 
>> I'm writing for a backend and have a complicated instruction bundle (3 
>> instructions) that has to be executed like a single block (meaning: if 
>> the first instruction is executed, all three have to be executed to 
>> obtain the result, though not necessarily without other instructions in 
>> between). Unfortunately, MachineCSE gets in the way sometimes and rips 
>> it apart.
>> 
>> Is there a way to stop CSE from doing its thing (common subexpression 
>> elimination) for certain instructions?
>> 
>> I've already tried glueing (gluing?) them together, but that doesn't 
>> seem to make a difference.
>> 
>> Regards,
>> Johannes Birgmeier
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