On 2022-05-02, Karl Berry <k...@freefriends.org> wrote: > - @echo '# dummy' >$@-t && $(am__mv) $@-t $@ > + @: >>$@ > > 1) does it actually speed anything up?
The answer seems to be a resounding "yes". I tried one of my packages on an old slow PC, and changing this one line in Makefile.in cuts almost 5 seconds off of the depfiles generation step in config.status. (All .deps directories manually deleted between runs as otherwise the rule commands will not be executed). Before (x5): % time config.status Makefile depfiles real 0m15.320s real 0m15.210s real 0m15.210s real 0m15.210s real 0m15.220s After (x5): % time config.status Makefile depfiles real 0m10.650s real 0m10.550s real 0m10.550s real 0m10.550s real 0m10.650s That 5 seconds is a relatively small part of total configure runtime but it is noticeable. So if make implementations have no problem including empty files (I tried a few and all seem OK with it) then it seems like a win. > 2) without the mv I fear we are no longer noticing write failure I think it's OK. All shells that I know of set a failure status when redirection fails, at least for simple commands like that. One possible gotcha is that redirections on the : command are not always reliably performed by older shells. There might not be any real world problem because configure sets SHELL in the Makefile to one that probably does not exhibit any problem. If it matters, performing the redirection with "exec" instead of ":" should work in every shell and have pretty much identical performance. Cheers, Nick
