On Thu, Aug 23, 2012 at 10:46 PM, Georg-Johann Lay <a...@gjlay.de> wrote:
> For the hook in question, it would be the same effort as far as > the hook is concerned: Ir really makes no difference if you > > - Pass X to the hook and return true or false > > - Pass X to the hook and return X or NULL_RTX. > > However, the latter interface is much more general and powerful and > allows to change X -- or simply leave it alone like in > legitimize_address (target_legitimize_combine or so). I did some experiments with your proposal, but it is not as simple as it is written above. We use existing insn as a testing place, where we stuff various combinations and call recog. After all processing, we have to restore insn to its original state and singal recog_for_combine caller that we recognized the combination, but with optional clobbers. So, calling sites only expect the confirmation/rejection of the proposed patterns, and in case of confirmation, recog_for_combine is allowed to decorate the pattern with optional clobbers. Your proposal that recog_for_combine changes the pattern is not what callers expect from this function. Probably, there are better places to implement target-dependent transformations, and leave recog_for_combine just the task to confirm that them combined pattern is OK. Uros.
