[Bug tree-optimization/18777] New: Redundant loop count insns in simple vectorized loop

["uros at kss-loka dot si" <gcc-bugzilla@gcc.gnu.org>]

The modifies testcase from PR18767 shows the problem where loop count variables
still remains in vectorized loop.
Compiling the modified testcase with 'g++ -O2 -march=pentium4 -ftree-vectorize'
following code is produced for the first loop:

        ...
        leal    -24(%ebp), %esi
        leal    -40(%ebp), %ebx
        leal    -56(%ebp), %ecx
        xorl    %eax, %eax
        xorl    %edx, %edx
.L2:
        addl    $1, %eax
        movaps  (%edx,%esi), %xmm0
        mulps   (%ebx,%edx), %xmm0
        movaps  %xmm0, (%edx,%ecx)
        addl    $16, %edx
        cmpl    $1, %eax
        jne     .L2
        ...

It looks that the compiler does not figure out that the conditional jump is
never taken.

However with 'g++ -O2 -march=pentium4 -ftree-vectorize -funroll-loops' generated
code is a lot better:

        ...
        movaps  -24(%ebp), %xmm0
        mulps   -40(%ebp), %xmm0
        movaps  %xmm0, -56(%ebp)
        ...

Uros.

-- 
           Summary: Redundant loop count insns in simple vectorized loop
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: uros at kss-loka dot si
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18777