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[Bug c++/71942] [ARM] Zero-extending whats allready zero-extended even when -O3
- From: "rearnsha at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 20 Jul 2016 09:21:29 +0000
- Subject: [Bug c++/71942] [ARM] Zero-extending whats allready zero-extended even when -O3
- Auto-submitted: auto-generated
- References: <bug-71942-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71942
Richard Earnshaw <rearnsha at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Target| |arm
Status|UNCONFIRMED |NEW
Last reconfirmed| |2016-07-20
Ever confirmed|0 |1
--- Comment #2 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
This is a well known problem. When a data object is marked volatile the
compiler is ultra-conservative about optimizing around it. The result is that
the load and the zero-extend get separated and then never merged back together
again.