[LLVMdev] adding support for -ffixed-<reg>

[Chris Lattner]

On Oct 3, 2012, at 12:13 AM, 陳韋任 (Wei-Ren Chen) <chenwj at iis.sinica.edu.tw> wrote:

> Hi Chris,
> 
>> From the design perspective, I think it would make sense to represent this in
>> LLVM IR with named metadata (http://llvm.org/docs/LangRef.html#
>> namedmetadatastructure) like "!llvm.fixedregs".  This could then be picked up
>> by the code generator, installed as preallocated registers (Jakob would be the
>> one to ask how best to do this).
> 
>  -ffixed-<reg> and global register seems do the same thing, they both
> reserve register from being used by the compiler. IIRC, you don't want
> to add global register support before. If so, why would you think
> -ffixed-<reg> is O.K.?

I'm not opposed to implementing support for global register variables, we just didn't have a way to model it well before.  Now we do!

-Chris