[Bug rtl-optimization/31806] New: miscompilation with -fschedule-insns2 -fthreadsafe-statics and static variables

[mueller at gcc dot gnu dot org]

Hi, 

the testcase below aborts with gcc 4.1.3 compiled with:
g++ -O2 -fno-threadsafe-statics

=== Cut ===
extern "C" void abort(void);

struct A
{
    void *d;
};

static const A& staticA()
{
    static A s_static;
    return s_static;
}

void assert_failed()
{
    abort();
}

A testMethod()
{
    static const A& s = staticA( );
    if (&s == 0)
        assert_failed();
    return s;
}

int main()
{
    testMethod();
    return 0;
}

// g++ -O2 -fno-inline -fno-threadsafe-statics -o kglobaltest kglobaltest.cpp
=== Cut ===

The testcase was extracted from a KDE miscompilation. -fno-schedule-insns2
seems to work around it. 

the bug is visible in assembler:

·       call·   _Z7staticAv·    #
·       movl·   _ZZ10testMethodvE1s, %ebx·      # s, s.1
·       movb·   $1, _ZGVZ10testMethodvE1s·      #,
·       testl·  %ebx, %ebx·     # s.1
·       movl·   %eax, _ZZ10testMethodvE1s·      # tmp61, s

the movl %eax,_ZZ10testMethodvE1s is moved below the movl·  
_ZZ10testMethodvE1s, %ebx, which causes the bug.


-- 
           Summary: miscompilation with -fschedule-insns2 -fthreadsafe-
                    statics and static variables
           Product: gcc
           Version: 4.1.3
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mueller at gcc dot gnu dot org
  GCC host triplet: i686-suse-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31806