• d-bugmail puremagic.com Apr 15 2007

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=1149

           Summary: Optimizer: obsolete array length loads, common subexpr.
                    elimin. not working
           Product: D
           Version: 1.012
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: jascha mainia.de


consider the following code:

void main()
{
    uint[] arr;
    arr.length = 4;
    arr[0] = 1;
    arr[1] = 1;
    arr[2] = 1;
    arr[3] = 1;
}

for the 4 assignments, "dmd -O -inline" generates

mov     ECX,1
mov     EDX,010h[ESP]
mov     EAX,0Ch[ESP]
mov     [EDX],ECX
mov     EDX,010h[ESP]
mov     EAX,0Ch[ESP]
mov     4[EDX],ECX
mov     EDX,010h[ESP]
mov     EAX,0Ch[ESP]
mov     8[EDX],ECX
mov     EDX,010h[ESP]
mov     EAX,0Ch[ESP]
mov     0Ch[EDX],ECX

instead of

mov     ECX,1
mov     EDX,010h[ESP]
mov     [EDX],ECX
mov     4[EDX],ECX
mov     8[EDX],ECX
mov     0Ch[EDX],ECX

- the length of the array is always loaded, even if it's not used
- the array pointer is loaded multiple times into the same register

the common subexpression elimination appears to be working for the value in
ECX, but not for the pointer in EDX.


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