[Bug rtl-optimization/56999] New: [4.8/4.9 Regression] LRA caused miscompilation of xulrunner

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56999

             Bug #: 56999
           Summary: [4.8/4.9 Regression] LRA caused miscompilation of
                    xulrunner
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jakub@gcc.gnu.org
                CC: vmakarov@gcc.gnu.org


With -fpic -O2 -m32 -march=i686 -mtune=atom the following testcase is
miscompiled with LRA (but, I don't have a runtime testcase, just eyeball
assembly right now).  The bad code is:
        movl    24(%esp), %eax
        addl    $12, %eax
        movl    %eax, 24(%esp)
        addl    $8, %eax
        testb   %cl, %cl
        movl    24(%esp), %ecx
        cmovne  %ecx, %eax
        movl    %eax, 24(%esp)
while reload has:
        movl    %ecx, %eax
        addl    $8, %ecx
        addl    $12, %eax
        cmpb    $0, 23(%esp)
        cmove   %ecx, %eax
instead.  So, reload performs the intentional ptr + (flag ? 12 : 8) while
the LRA code performs ptr + (flag ? 12 : 20) instead.  The source code related
to this is barriers ? &mJITInfo->jitHandleCtorBarriered :
&mJITInfo->jitHandleCtor where offsetof (JITScriptSet, jitHandleCtorBarriered)
== 12 and offsetof (JITScriptSet, jitHandleCtor) is 8, there is no field at
offset 20.