llvm dev - Feb 2009 - [LLVMdev] rol/ror llvm instruction set

Hi,

I was looking around the LLVM instruction set and I failed to find ROL and ROR
instructions. Is there any plans on adding these instructions to LLVM?

The reason that I am asking is for cryptographical algorithms which are becoming
ever more important rotation is a major operation. Thus including such
instruction could reduce 3 instructions {shl, shr, or} into {rol | ror} which
could gain considerable performance. However, the increased performance is not
confined within crypto algorithms.


-- Kasra

On Feb 3, 2009, at 2:28 PM, Kasra wrote:
> I was looking around the LLVM instruction set and I failed to find  
> ROL and ROR instructions. Is there any plans on adding these  
> instructions to LLVM?
Not sure what you mean:

  $ cat t.c
unsigned int rol(unsigned int i) {
   return i << 1 | i >> 31;
}
mrs $ clang -S t.c -O2
mrs $ cat t.s


	.text
	.align	4,0x90
	.globl	_rol
_rol:
	movl	4(%esp), %eax
	roll	%eax
	ret

?

On Feb 3, 2009, at 2:35 PMPST, Mike Stump wrote:
> On Feb 3, 2009, at 2:28 PM, Kasra wrote:
>> I was looking around the LLVM instruction set and I failed to find
>> ROL and ROR instructions. Is there any plans on adding these
>> instructions to LLVM?
>
> Not sure what you mean:
He's referring to the LLVM IR, I think, and it's true that doesn't  
have rotates.  The LLVM back ends do know about rotate instructions on  
targets that have them, though, and the llvm optimizers are pretty  
smart about recognizing the usual ways to express rotate with shift/ 
and/or, as below.
>  $ cat t.c
> unsigned int rol(unsigned int i) {
>   return i << 1 | i >> 31;
> }
> mrs $ clang -S t.c -O2
> mrs $ cat t.s
>
>
> 	.text
> 	.align	4,0x90
> 	.globl	_rol
> _rol:
> 	movl	4(%esp), %eax
> 	roll	%eax
> 	ret
>
> ?
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