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.