[LLVMdev] Fast register allocation

[Evan Cheng]

On May 18, 2010, at 9:03 AM, Jakob Stoklund Olesen <stoklund at 2pi.dk> wrote:

> 
> On May 18, 2010, at 8:23 AM, Daniel Dunbar wrote:
> 
>> You mention some potential issues on ARM, should we sort those out
>> before we enable it in Clang? It's somewhat more convenient to have
>> things be consistent.
> 
> Sure, I'll be testing some ARM code today. There is also Evan's new REG_SEQUENCE instruction to verify.
> 
>> I propose that at some point you just replace the old local register
>> allocator with the new one, and rename the old one. Then clients don't
>> need to change, and we can keep the old one available for a little
>> while if we want, for testing.
> 
> I am not a big fan of renaming - it can easily cause confusion. Besides, fast-alloc goes with fast-isel.
> 
> But perhaps we could take this opportunity to let LLVMTargetMachine choose a register allocator based on the optimization level? It is already enabling fast-isel that way, and -O0 -regalloc=linearscan (which is the default) doesn't really make sense.
> 
> LLVMTargetMachine::addCommonCodeGenPasses does a decent job of building a codegen pipeline, except it needs help picking a register allocator. There is no good reason for that.

Agreed. 

Evan

> 
> /jakob
> 
> 
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