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Date: Wed, 12 May 2010 13:08:00 -0000
From: "mjw at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: systemtap@sources.redhat.com
Message-ID: <20100512092821.11590.mjw@redhat.com>
Reply-To: sourceware-bugzilla@sourceware.org
Subject: [Bug translator/11590] New: optimized pre/postfix operators on variable throw away initial variable assignment
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The following testcase shows that the original assignment of the variable is
ignored:

probe begin {

        a = 5

        // printf("%d ", a)
        printf("%d ", (a++))
        printf("%d ", (++a))
        printf("%d ", (a--))
        printf("%d\n", (--a))
        exit()
}

$ stap test.stp
0 2 2 0

If we uncomment the actually first use the original assigned value of a things
look correct:

$ stap test.stp
5 5 7 7 5

This is an translation optimization issue, the original script also prints out
the correct value when unoptimized:

$ stap -u test.stp
5 7 7 5

-- 
           Summary: optimized pre/postfix operators on variable throw away
                    initial variable assignment
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: mjw at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=11590

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