Path: csiph.com!weretis.net!feeder6.news.weretis.net!news.misty.com!news.iecc.com!.POSTED.news.iecc.com!nerds-end From: anton@mips.complang.tuwien.ac.at Newsgroups: comp.compilers Subject: Re: Interpreters and caller-saved registers Date: Thu, 19 Oct 2023 17:14:28 +0000 Organization: Compilers Central Sender: johnl%iecc.com Approved: comp.compilers@iecc.com Message-ID: <23-10-003@comp.compilers> References: <23-10-001@comp.compilers> <23-10-002@comp.compilers> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Injection-Info: gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="87340"; mail-complaints-to="abuse@iecc.com" Keywords: interpreter, optimize Posted-Date: 19 Oct 2023 14:51:59 EDT X-submission-address: compilers@iecc.com X-moderator-address: compilers-request@iecc.com X-FAQ-and-archives: http://compilers.iecc.com Xref: csiph.com comp.compilers:3530 Thomas Koenig writes: >It is well known that compilers in general and gcc specfically often >generate superflous register moves ... >However, if this got worse between releases, this is a regression. >Those get higher priority for fixing. So, if it is reasonable >to generate a reduced test case (for which cvise, for example, >is an excellent tool) so filing a bug report would be a good thing. If you want to file such a bug report, I can give you the commit of Gforth before we added all the workarounds, where all the problems are visible without ado. >This sort of code is an example of the contradictions in today's >compiler technology. On the one hand, they do amazing optimizations >on large amounts of code which no programmer could hope to reach >while staying productive. There are certainly cases where compilers loop-unroll (plus ramp-up/down and compensation code) code into huge swaths of code that makes it hard to see where the action is going on, but amazing? >So far, nobody has found an algorithm for "just remove the >silliness" from compiled programs. Maybe it would be feasible to >run some peephole optimization as last passes which could improve >code like the one above, but that might also be difficult in the >more general case where registers are reused in other basic blocks >(which would mean just to redo the register allocation). Yes, I doubt that it can be solved with peephole optimization, or it would have been done already. - anton -- M. Anton Ertl anton@mips.complang.tuwien.ac.at http://www.complang.tuwien.ac.at/anton/