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Re: optimization/5738: GCSE missed optimization
- From: rth at gcc dot gnu dot org
- To: dann at godzilla dot ics dot uci dot edu, gcc-bugs at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, nobody at gcc dot gnu dot org
- Date: 3 Apr 2002 10:25:10 -0000
- Subject: Re: optimization/5738: GCSE missed optimization
- Reply-to: rth at gcc dot gnu dot org, dann at godzilla dot ics dot uci dot edu, gcc-bugs at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, nobody at gcc dot gnu dot org, gcc-gnats at gcc dot gnu dot org
Synopsis: GCSE missed optimization
State-Changed-From-To: open->closed
State-Changed-By: rth
State-Changed-When: Wed Apr 3 02:25:09 2002
State-Changed-Why:
That's not how partial redundancy elimination (PRE) works.
The object with PRE is to minimize the number of evaluations
of an expression *along a path*. There is already one
evaluation along each path, thus PRE considers things
optimal.
You want global value numbering or something, which we
don't implement.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5738