[Bug middle-end/54985] New: Dom optimization erroneous remove conditional goto.

[vbyakovl23 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54985

             Bug #: 54985
           Summary: Dom optimization erroneous remove conditional goto.
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: vbyakov...@gmail.com


Attached test case fails if compiled with -O1 and higher.

gcc -O0 -m32  q.c qm.c  ; ./a.out && echo "pass" || echo "FAIL"                 
pass
gcc -g3 -O1 -m32  q.c qm.c  ; ./a.out && echo "pass" || echo "FAIL"             
FAIL

gcc -v
Using built-in specs.
COLLECT_GCC=/export/users/vbyakovl/workspaces/gcc/install-ref/bin/gcc
COLLECT_LTO_WRAPPER=/export/users/vbyakovl/workspaces/gcc/install-ref/libexec/gcc/x86_64-unknown-linux-gnu/4.8.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc/configure CFLAGS='-O0 -g3'
--prefix=/export/users/vbyakovl/workspaces/gcc/install-ref --disable-bootstrap
--enable-languages=c,c++,fortran,lto CXXFLAGS='-O0 -g3' : (reconfigured)
../gcc/configure CFLAGS='-O0 -g3'
--prefix=/export/users/vbyakovl/workspaces/gcc/install-ref --disable-bootstrap
CXXFLAGS='-O0 -g3' --enable-languages=c,c++,fortran,lto --no-create
--no-recursion : (reconfigured) ../gcc/configure CFLAGS='-O0 -g3'
--prefix=/export/users/vbyakovl/workspaces/gcc/install-ref --disable-bootstrap
CXXFLAGS='-O0 -g3' --enable-languages=c,c++,fortran,lto --no-create
--no-recursion
Thread model: posix
gcc version 4.8.0 20121015 (experimental) (GCC)

Wrong compilation of a routine

int foo(ST *s, int c)
{
    int first = 1;
    int count = c;
    ST *item = s;
    int a = s->a;
    int x;

    while (count--)
    {  
        x = item->a;
        if (first)
            first = 0;
        else if (x >= a)
            return 1;
        a = x;
        item++;
    }
    return 0;
}

Compiler sets equivalence between ‘x’ and ‘a’ (routine tree-ssa-threadedge.c
/record_temporary_equivalences_from_phis() ) and folds comparison x >= a to
true.