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Date: Sat, 26 Sep 2009 18:02:00 -0000
Subject: [Bug c/41477]  New: gcc does not optimize a case that it should to make __builtin_object_size() more useful
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From: "arjan at linux dot intel dot com" <gcc-bugzilla@gcc.gnu.org>
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(see attached testcases; testcase.c shows the problem, testcase2.c shows that
reorging the code works around it)

it appears that gcc does not realize that after

if (variable < 1 || variable > 10)
     return -1;

the "variable" is in the range [1..10], likely because the execution of the
second check is optional due to the ||.

in a typical __builtin_object_size() scenario, like

if (__builtin_object_size(foo) < variable)
    some_error();

where foo is 10 bytes in size, this means the check does not get optimized out.


-- 
           Summary: gcc does not optimize a case that it should to make
                    __builtin_object_size() more useful
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: arjan at linux dot intel dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41477