From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeffrey A Law To: David Edelsohn Cc: Zack Weinberg , Jamie Lokier , egcs@egcs.cygnus.com Subject: Re: gcc-2.7 creates faster code than pgcc-1.1.1 Date: Wed, 31 Mar 1999 23:46:00 -0000 Message-ID: <13939.920608288@hurl.cygnus.com> References: <9903050403.AA36338@marc.watson.ibm.com> X-SW-Source: 1999-03n/msg00208.html Message-ID: <19990331234600.nXVE8XRD2P04AUQ3OzC8Uje6tlGt1Q6CFmXra8fxtuE@z> In message < 9903050403.AA36338@marc.watson.ibm.com >you write: > GCC is missing a general feature of value propagation which would > help with a lot of optimizations like this. Hopefully this infrastructure > will be added or contributed someday. Most of the papers I've read have indicated only trivial gains from value range propagation. I've also had discussions with folks that have implemented this opt in a commercial compiler -- it's so minor of a win that they didn't consider it worth the effort. It's best use appears to be for optimizing array bounds checking in languages that require such checks. jeff