llvm dev - Nov 2012 - [LLVMdev] which Register allocator to use with llc -O0

Hi,
 
We were using "linearscan" register scan with llc -O0 option. As per
the llvm blog, this is replaced with greedy register alloation.
http://blog.llvm.org/2011/09/greedy-register-allocation-in-llvm-30.html
 
But I think, this register allocation (i.e. 'greedy and 'basic') is
blocked if used with -O0 option of llc. Only 'fast register allocator'
option can be used with -O0.
 
I wanted to understand that what will be consequence of forcefully enabling
'greedy allocation' ?
 
Regards,
Pankaj
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On Nov 6, 2012, at 6:59 AM, Pankaj Gode <godepankaj at yahoo.com> wrote:
> Hi,
>  
> We were using "linearscan" register scan with llc -O0 option. As
per the llvm blog, this is replaced with greedy register alloation.
> http://blog.llvm.org/2011/09/greedy-register-allocation-in-llvm-30.html
>  
> But I think, this register allocation (i.e. 'greedy and
'basic') is blocked if used with -O0 option of llc. Only 'fast
register allocator' option can be used with -O0.
>  
> I wanted to understand that what will be consequence of forcefully enabling
'greedy allocation' ?
You can use RAGreedy with -O0, but you need to enable the full optimizing
register allocation pipeline:

$ llc -O0 -optimize-regalloc

Same thing if you want to use RABasic.

/jakob

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