[LLVMdev] predicates and conditional execution

[roy rosen]

2011/5/24 Justin Holewinski <justin.holewinski at gmail.com>:
> On Tue, May 24, 2011 at 3:02 AM, roy rosen <roy.1rosen at gmail.com> wrote:
>>
>> Hi,
>>
>> I was wondering if LLVM supports predicates and conditional execution.
>> Something like we have in IA64.
>> There is a register class of predicates and then every instruction may
>> be predicated by a register from this class.
>> For example:
>>
>> cmp_less p, x, y // p is a predicate which gets the result of x < y
>> p add x, x, 2 // if p then do the add instruction
>>
>> Is there support in LLVM to something like that?
>>
>> Which architecture can show a good example for the implementation of that?
>
> You may want to look at the PTX back-end.  The PTX assembly language
> supports exactly what you are describing, and we currently use it to
> implement conditional branching.  There is a register class for predicates
> (i1 in LLVM) and all machine instructions have a predicate operand and
> predicate filter (PTX supports inverted predicates).  For un-predicated
> instructions, the predicate operand is just set to the special NoRegister
> constant.
>
>>
>> Thanks, Roy.
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>
>
> --
>
> Thanks,
> Justin Holewinski
>

I see that PTX has predicated execution for all instructions.
in LLVM you implement conditional execution only for branches?
Do you know what it takes to make it work for all instructions?

Thanks, Roy.