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From: "hp at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug rtl-optimization/53908] New: [4.7 Regression] csa removes needed memory load
Date: Tue, 10 Jul 2012 03:06:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53908

             Bug #: 53908
           Summary: [4.7 Regression] csa removes needed memory load
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hp@gcc.gnu.org
              Host: x86_64-linux
            Target: x86_64-linux-gnu, cris-axis-elf,
                    crisv32-axis-linux-gnu


Created attachment 27768
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27768
Repeat with e.g. cc1 -O2 ba2.c

Observed with gcc-4_7-branch revision 189394.
The attached test-case calls
is_basic(user_name) < 0 && is_digest(user_name) < 0
with *user_name = NULL.
The call to is_basic "fails"; returns < 0 without writing to *user_name.
The call to is_digest is successful and furthermore writes *user_name (a char
**).  Next, *user_item = find_user(*user_name) is called, but the load of
*user_name after the is_digest call is lost; wrongly eliminated in favor of the
load after the call to is_basic.

A dump shows wrong code first in the ".207r.csa" pass (for
crisv32-axis-linux-gnu, likely for x86_64 as well).

The test-case does not expose the bug on trunk r189401.
Not observed with a gcc-4.3-based toolchain (cris-*), not observed with (host)
"Debian 4.4.5-8". Unknown 4.5, 4.6.