llvm dev - Jul 2012 - [LLVMdev] Bind a LLVM variable to a CPU register

I have a constant parameter in a LLVM function. Is there a way to
reserve a CPU register such that it also holds the value of the
parameter in LLVM x86 codegen ?

Thanks

Xin

put "register" keyword on that variable.

E.g.,
register int i;
...

Whether it will be register allocated is totally up to the compiler, 
with respect to the rest of the program.

Chuck

On 7/19/2012 11:14 AM, Xin Tong wrote:
> I have a constant parameter in a LLVM function. Is there a way to
> reserve a CPU register such that it also holds the value of the
> parameter in LLVM x86 codegen ?
>
> Thanks
>
> Xin
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

Not really, no.

On Jul 19, 2012, at 11:14 AM, Xin Tong <xerox.time.tech at gmail.com>
wrote:
> I have a constant parameter in a LLVM function. Is there a way to
> reserve a CPU register such that it also holds the value of the
> parameter in LLVM x86 codegen ?
> 
> Thanks
> 
> Xin
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

On 7/19/12 1:23 PM, Jim Grosbach wrote:
> Not really, no.
If you really, really, wanted to do it, you could:

1) Hack the code generator to not use that register.  It might be as 
simple as modifying the TableGen file to not know that the register exists.
2) Use inline asm to put the constant into that register and fetch it 
from that register.

The real question is: what larger goal are you trying to accomplish?  
Holding a constant value in a register might not be the best way to do 
what you're doing.

-- John T.
>
> On Jul 19, 2012, at 11:14 AM, Xin Tong <xerox.time.tech at gmail.com>
wrote:
>
>> I have a constant parameter in a LLVM function. Is there a way to
>> reserve a CPU register such that it also holds the value of the
>> parameter in LLVM x86 codegen ?
>>
>> Thanks
>>
>> Xin
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

> E.g.,
> register int i;
> ...
>
> Whether it will be register allocated is totally up to the compiler,
> with respect to the rest of the program.
Yeah, e.g. clang just ignores "register" keyword :)

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University