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

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

[uros at kss-loka dot si]

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

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

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization


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

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

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-12-02 13:31 -------
I think this is related to PR 18557.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |18557


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

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

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-06-12 03:19 -------
Fixed on the mainline:
_Z6foobarv:
.LFB2:
        pushl   %ebp
.LCFI0:
        movl    %esp, %ebp
.LCFI1:
        subl    $56, %esp
.LCFI2:
        movaps  -40(%ebp), %xmm0
        mulps   -24(%ebp), %xmm0
        movaps  %xmm0, -56(%ebp)
        fldz
        fadds   -56(%ebp)
        fadds   -52(%ebp)
        fadds   -48(%ebp)
        fadds   -44(%ebp)
        leave
        ret

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.1.0


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