[LLVMdev] how to turn off conversion of add's into or's (in address calculations)

[Matt Arsenault]

On 06/06/2014 09:38 AM, Jingyue Wu wrote:
> HI Helkki,
>
> I guess instcombine does that. See InstCombineAddSub.cpp:1107. The 
> optimization there is more general than converting address computation 
> adds. If A and B don't have common bits, instcombine converts A + B to 
> A | B. I am not aware of any configuration to turn this particular 
> optimization off. If you just want to experiment, you can always 
> change the code. Or you can improve your analysis/optimization to 
> treat such OR as ADD.
>
> Ignore if you already know this: you can run "opt -O3 
> -print-after-all" to figure out which optimization pass does a certain 
> thing.
>
> Jingyue
Add the IR level, most / nearly all address calculations are hidden in 
GEPs. They are only really exposed later in SelectionDAG, so DAGCombiner 
is probably doing this

>
>
> On Fri, Jun 6, 2014 at 6:11 AM, Heikki Kultala <hkultala at cs.tut.fi 
> <mailto:hkultala at cs.tut.fi>> wrote:
>
>     It seems some optimization pass converts some address computation
>     add's into or's when it knows it's allowed due correct alignment.
>
>     How do I turn this off keep the address calculations as adds?
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