On Tue, Jul 11, 2017 at 2:26 AM, Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx> wrote: >> >> You are right. I will never consider 2) as my goal. Simply because >> if the compiler has to depend on certain order of optimization (delete >> dead BB vs memops, CSE) and it can't figure out the order by itself. >> Then I consider a bug in the compiler. > > You may qualify this as a bug but in the real world it's totally > normal to have interactions between optimization passes (yes, this > means that the result will depend on the order of the passes). > This is especially true when it concern dead code elimination. > > Any decent compiler book will tell you a bit more about this. OK. Apparently I haven't read any decent compiler books yet, that is why I am not a good maintainer. My sentence have two parts. You only read the first part about the ordering. The second part you seem missing is that, if the order make a difference, *and* the compiler can't to figure out a the (optimal) order by itself, that is a bug. It is just command sense. If I re-order my C source file with some goto and moving code blocks around. The C compiler should generate pretty much the same optimal code in the end. If your investigation of comparing two approach to compile the same source code, your patch generate better result. Then we need to look at it. That might be reason to use your patch. Maybe there is some other simple way to modify my patch to generate as good a result as well. Do you have any example you believe my simpler approach will generate worse code then your not so complicate approach? > But well, you're the maintainer, it's your responsability to > make the good choices for the project. Of course. I try really hard to make the right choice. I can only make decision base on the information I have in hand. So far you haven't conclude your investigation that the simpler approach will generate worse code. You said it is different, different can be better or be worse. If it turn out to be different but equivalent, then why not just use the simpler approach? If it is not, then let's look at why this pack blocks earlier will make code better. Make some adjustment in the code, possible remove dead block earlier like your patch suggested. Chris PS, Any decent compiler book you want to recommend? I want to see it. -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
