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Date: Sun, 07 Mar 2004 01:34:00 -0000
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From: "pinskia at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug optimization/12771] Weak loop optimizer
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X-SW-Source: 2004-03/txt/msg00855.txt.bz2
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------- Additional Comments From pinskia at gcc dot gnu dot org  2004-03-07 01:34 -------
The mainline has changed but still the same number of memory accesses:
        movl    16(%ebp), %edx
        flds    (%edx,%eax,4)
        fmul    %st(1), %st
        fadds   (%esi,%eax,4)
        fstps   (%esi,%eax,4)
        incl    %eax
On the other hand with -freduce-all-givs, it has increased by one:
.L15:
        flds    (%ecx)
        addl    $4, %ecx
        fmul    %st(1), %st
        fadds   (%eax)
        fstps   (%eax)
        addl    $4, %eax
        decl    %edx
        jne     .L15
Here is the reduced source:
void daxpy(int n, float  da, float  dx[], int incx, float  dy[], int incy)
{
        int i,ix,iy,m,mp1;

        mp1 = 0;
        m = 0;

        if(n <= 0) return;
        if (da == 0.0 ) return;

        if(incx != 1 || incy != 1) {
                ix = 0;
                iy = 0;
                if(incx < 0) ix = (-n+1)*incx;
                if(incy < 0)iy = (-n+1)*incy;
                for (i = 0;i < n; i++) {
                        dy[iy] = dy[iy] + da*dx[ix];
                        ix = ix + incx;
                        iy = iy + incy;
                }
                return;
        }
        for (i = 0;i < n; i++) {
                dy[i] = dy[i] + da*dx[i];
        }
return;
}

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2003-10-28 15:38:57         |2004-03-07 01:34:09
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12771