[LLVMdev] Stop MachineCSE on certain instructions

[Evan Cheng]

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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