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From: "gjl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/50223] AVRGCC - dont clear r26 and r27.....its a (small) waste of CPU cycles.
Date: Wed, 31 Aug 2011 20:48:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50223

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
                 CC|                            |gjl at gcc dot gnu.org

--- Comment #1 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-08-31 20:23:25 UTC ---
This is just a missed optimization. Thus, you won't see a fix before gcc 4.7.

For gcc 4.7, notice that there are optimized versions of builtins that perform
your arithmetic like

__builtin_clz/clzl/clzll (count leading zeros)
__builtin_ctz/ctzl/ctzll (count trailing zeros)
__builtin_ffs/ffsl/ffsll (find first (lowest) set bit)
...