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[Bug rtl-optimization/39543] [4.4/4.5 Regression] Reload failure on mplayer from SVN
- From: "matz at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 14 Apr 2009 13:58:59 -0000
- Subject: [Bug rtl-optimization/39543] [4.4/4.5 Regression] Reload failure on mplayer from SVN
- References: <bug-39543-87@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #12 from matz at gcc dot gnu dot org 2009-04-14 13:58 -------
That's only possible sometimes and hence can't be relied upon. The RHS
expression might not be available at the point of the use anymore (some
operands might have been clobbered meanwhile, remember we aren't in SSA
anymore). That's one of the reasons why TER doesn't forward all expressions
even if they're used only once.
To really fix this for good it needs a separate pass tracking lifetime (and
introducing copies in case the operands aren't available) or working on SSA
form (where lifetime isn't a problem and copies would be inserted by
out-of-SSA).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39543