[RFC] Use which_alternative in preparation-statements of define_insn_and_split

[Richard Earnshaw]

On 22/11/11 19:06, Richard Henderson wrote:
> On 11/21/2011 05:38 PM, Jiangning Liu wrote:
>> But I still want to know why we don't want to support this? I don't see any
>> GCC documentation saying not allowing this usage.
> 
> Before reload, which_alternative doesn't make much sense, yet you compute it anyway.  After reload, but for raw define_split, which_alternative doesn't make much sense, yet you compute it anyway.
> 
> Now, either or both are fixable, but instead it seemed to me like maybe you were going down the wrong path entirely.
> 
> 
> r~
> 

Plus extract_insn is a moderately expensive operation, given that we
have to scan all the alternatives in an insn to find the matching one.

I wouldn't have thought it was generally something we would want to do
on every split pattern we apply unless it is really needed.

R.