[Bug rtl-optimization/20376] The missed-optimization of general induction variables in the new rtl-level loop optimizer cause performance degradation.

[canqun at nudt dot edu dot cn]

------- Additional Comments From canqun at nudt dot edu dot cn  2005-03-30 14:42 -------
(In reply to comment #7)
> Waiting for a test case...

Part 1
! Test sase for address giv (general induction variable) optimization.
subroutine dot_product (sum, a, b, n)
   real*8 a(n), b(n), sum
   sum = 0
   do i = 1, n
     sum = sum + a (i) * b(i)
   end do
end

Part 2
// IA-64 Assembly code generated by GCC without address giv splitting
        mov ar.lc = r14
.L4:
// Loop is unrolled, but the address givs are not splitted.
// Register r17, r19 is used to calculate all the addresses
// of the array elements.
        .mmb
        ldfd f7 = [r17]
        ldfd f6 = [r19]
        nop 0
        .mmi
        add r17 = r15, r33
        add r19 = r15, r34
        shladd r15 = r18, 3, r0
        ;;
        .mmf
        nop 0
        nop 0
        fma.d f8 = f7, f6, f9
        .mmi
        ldfd f7 = [r17]
        ldfd f6 = [r19]
        add r17 = r15, r33
        .mfi
     nop 0
        shladd r15 = r16, 3, r0
        ;;
        .mmf
        nop 0
        nop 0
        fma.d f8 = f7, f6, f8
        .mmi
        ldfd f7 = [r17]
        ldfd f6 = [r19]
        add r17 = r15, r33
        .mmb
        nop 0
        add r19 = r15, r34
        nop 0
        ;;
        .mmf
        nop 0
        nop 0
        fma.d f8 = f7, f6, f8
        .mmb
        ldfd f7 = [r17]
        ldfd f6 = [r19]
        nop 0
        ;;
        .mmf
        nop 0
        nop 0
        fma.d f8 = f7, f6, f8
        ;;
        .mfb
        nop 0
        mov f9 = f8
        br.cloop.sptk.few .L4
        ...
        .endp dot_product__#
        .ident  "GCC: (GNU) 4.1.0 20050302 (experimental)"

Part 3
// IA-64 assembly code generated by GCC with address giv splitting
        mov ar.lc = r16
.L28:
[.L3:]
[.L2:]
        ...
// The loop is unrolled, and the address givs are splitted.
// Register r14, r8, r3, r35, r33, r31,r28, r29 is used to
// caculate the address of each array element respectively.
        .mmi
        ldfd f38 = [r14]
        ldfd f39 = [r8]
        add r31 = r34, r23
        .mmi
        ldfd f35 = [r3]
        ldfd f37 = [r35]
        add r33 = r34, r24
        ;;
        .mmb
        ldfd f33 = [r33]
        ldfd f34 = [r31]
        nop 0
        .mmi
        add r28 = r30, r23
        add r29 = r30, r24
        adds r22 = 4, r22
        ;;
        .mmf
        ldfd f32 = [r29]
        ldfd f15 = [r28]
        fma.d f36 = f38, f39, f14
        ;;
        .mmf
        nop 0
        nop 0
        fma.d f13 = f35, f37, f36
        ;;
        .mmf
        nop 0
        nop 0
        fma.d f12 = f33, f34, f13
        ;;
        .mfb
        nop 0
        fma.d f14 = f32, f15, f12
        br.cloop.sptk.few .L28
        ;;
.L9:
        .mfb
        stfd [r32] = f14
        nop 0
        nop 0
        ...
        .endp dot_product__#
        .ident  "GCC: (GNU) 3.5-tree-ssa 20031221 (CCRG)"

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20376