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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/63660] -Wmaybe-uninitialized false positive with -O1 and more
Date: Tue, 28 Oct 2014 09:04:00 -0000
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X-Bugzilla-Type: changed
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 4.8.0
X-Bugzilla-Keywords: diagnostic
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63660

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-10-28
          Component|driver                      |tree-optimization
            Summary|[4.8-4.9+]                  |-Wmaybe-uninitialized false
                   |-Wmaybe-uninitialized false |positive with -O1 and more
                   |positive with -O1 and more  |
     Ever confirmed|0                           |1
      Known to fail|                            |4.8.3, 4.9.2, 5.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think you hit one of the limits to avoid excessive compile-time for the
uninit analysis:

#define MAX_NUM_CHAINS 8
#define MAX_CHAIN_LEN 5
#define MAX_POSTDOM_CHECK 8

I suppose it's the MAX_POSTDOM_CHECK value.  Sadly those are not parameters
controllable by any --param.

There is --param uninit-control-dep-attempts though (but its default is 1000
which the testcase probably doesn't hit).

Confirmed with 4.8, 4.9 and 5.