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From: "amylaar at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/50729] [4.7 Regression] Silent code gen fault: Value range propagation seems to propagate values across narrowing/widening
Date: Sat, 19 Nov 2011 02:05:00 -0000	[thread overview]
Message-ID: <bug-50729-4-VPTBLDE9Nb@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-50729-4@http.gcc.gnu.org/bugzilla/>

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50729

--- Comment #8 from Jorn Wolfgang Rennecke <amylaar at gcc dot gnu.org> 2011-11-19 00:03:56 UTC ---
More specifically, the problem appears when innerop has a different signedness
than middleop, and the value range of middleop is such that the topmost bit
of a double_int is used.
E.g. the full value range of a 64 bit long long with 32 bit HOST_WIDE_INT,
or a 128 bit integer type with a 64 bit HOST_WIDE_INT.

OTOH both the old and the new test will reject some simplifications that
would be OK when considering a narrow finaltype, and/or same-size
signed/unsigned conversion.

The basic problem is that when a signedness change happens, we are no longer
necessarily considering a single range, but possibly two.


  parent reply	other threads:[~2011-11-19  0:05 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-10-14 13:40 [Bug tree-optimization/50729] New: " mgretton at sourceware dot org
2011-10-14 13:41 ` [Bug tree-optimization/50729] " mgretton at sourceware dot org
2011-10-14 13:49 ` mgretton at sourceware dot org
2011-10-14 13:50 ` mgretton at sourceware dot org
2011-10-14 14:04 ` [Bug tree-optimization/50729] [4.7 Regression] " rguenth at gcc dot gnu.org
2011-10-17 12:24 ` rguenth at gcc dot gnu.org
2011-10-17 12:57 ` rguenth at gcc dot gnu.org
2011-11-18 23:24 ` amylaar at gcc dot gnu.org
2011-11-19  2:05 ` amylaar at gcc dot gnu.org [this message]
2011-11-19  4:25 ` amylaar at gcc dot gnu.org
2011-12-06 12:05 ` rguenth at gcc dot gnu.org

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