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Re: gcc-2.7 creates faster code than pgcc-1.1.1
- To: David Edelsohn <dje at watson dot ibm dot com>
- Subject: Re: gcc-2.7 creates faster code than pgcc-1.1.1
- From: Jeffrey A Law <law at hurl dot cygnus dot com>
- Date: Thu, 04 Mar 1999 21:31:28 -0700
- cc: Zack Weinberg <zack at rabi dot columbia dot edu>, Jamie Lokier <egcs at tantalophile dot demon dot co dot uk>, egcs at egcs dot cygnus dot com
- Reply-To: law at cygnus dot com
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.