[LLVMdev] [PATCH] Emit rbit, clz on ARM for __builtin_ctz

[Jim Grosbach]

On Jan 18, 2010, at 11:07 AM, Evan Cheng wrote:

> 
> On Jan 15, 2010, at 2:52 PM, Jim Grosbach wrote:
> 
>> 
>> On Jan 15, 2010, at 11:37 AM, Richard Osborne wrote:
>> 
>>> 
>>> On 15 Jan 2010, at 18:03, Chris Lattner wrote:
>>> 
>>>> On Jan 14, 2010, at 10:13 PM, David Conrad wrote:
>>>> 
>>>>> Other targets that I know of that could potentially benefit from
>>>>> this optimization being global (that have a clz and bitreverse
>>>>> instruction but not ctz) are AVR32 and C64x, neither of which llvm
>>>>> has backends for yet.
>>>> 
>>>> When/if another target wants this, we could add a ISD::RBIT  
>>>> operation,
>>>> it doesn't need to be added at the llvm ir level,
>>> 
>>> The XCore also has ctlz and bitreverse instructions and not cttz. At  
>>> the moment in the XCore backend cttz is marked as legal and expanded  
>>> to this pair of instructions in a pattern in the InstrInfo.td.
>> 
>> In that case, perhaps it makes sense to add it as an ISD::RBIT  
>> operation straight away.
> 
> Since only a couple of targets can use this, it shouldn't block this patch from going in. Jim, can you commit this?
> 

Works for me. Done in r93758.

Thanks for doing this, David.

-Jim