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From: "jasonwucj at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/58295] [4.8/4.9 regression] Missed zero-extension elimination in the combiner
Date: Fri, 06 Sep 2013 09:54:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58295

Chung-Ju Wu <jasonwucj at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |jasonwucj at gmail dot com

--- Comment #2 from Chung-Ju Wu <jasonwucj at gmail dot com> ---
(In reply to Eric Botcazou from comment #1)
> combiner was indeed clever enough to do it.  The QI subreg is clearly
> problematic for the ARM here (and probably most RISC architectures).

Yes.  This problem also happens on our Andes nds32 architecture.
(The 'nds32' port is still awaiting for GWP approval before it
 may be committed.  But one can find its initial patch:
 http://gcc.gnu.org/ml/gcc-patches/2013-08/msg01441.html)

As long as we revert r191928, which is the fix for pr54457, and
design the pattern in nds32.md to recognize the insn that
combiner created, the redundant insn 10 can be eliminated.