[Issue 10685] Immutable interval foreach to propagate index value range

d-bugmail at puremagic.com d-bugmail at puremagic.com
Sat Jul 20 14:22:10 PDT 2013


http://d.puremagic.com/issues/show_bug.cgi?id=10685



--- Comment #1 from bearophile_hugs at eml.cc 2013-07-20 14:22:09 PDT ---
This range propagation is also useful for array bounds. See this code:


void main() {
    int[100] a;
    foreach (immutable i; 0 .. 10)
        a[i] = 1;
}


Compiled with DMD gives:

_D4test7__arrayZ:
L0:        enter    4,0
        push    EAX
        mov    ECX,offset FLAT:_D4test12__ModuleInfoZ
        push    ECX
        call    near ptr __d_array_bounds

__Dmain:
L0:     enter   0198h,0
        push    EBX
        push    ESI
        push    EDI
        mov ECX,064h
        xor EAX,EAX
        lea EDI,-0198h[EBP]
        rep
        stosd
        mov -8[EBP],EAX
L19:    cmp dword ptr -8[EBP],0Ah
        jge L4B
        mov ECX,-8[EBP]
        mov -4[EBP],ECX
        mov EDX,-4[EBP]
        cmp EDX,064h
        jb  L37
        mov EAX,4
        call    near ptr _D4test7__arrayZ
L37:    mov EBX,1
        mov ESI,-4[EBP]
        mov -0198h[ESI*4][EBP],EBX
        inc dword ptr -8[EBP]
        jmp short   L19
L4B:    xor EAX,EAX
        pop EDI
        pop ESI
        pop EBX
        leave
        ret


If the range of 'i' is propagated dmd could generate code like, thanks to Issue
9097 already implemented:


__Dmain:
        enter   0198h,0
        push    EBX
        push    EDI
        mov ECX,064h
        xor EAX,EAX
        lea EDI,-0198h[EBP]
        rep
        stosd
        mov -8[EBP],EAX
L18:    cmp dword ptr -8[EBP],0Ah
        jge L38
        mov ECX,-8[EBP]
        mov -4[EBP],ECX
        mov EDX,1
        mov EBX,-4[EBP]
        mov -0198h[EBX*4][EBP],EDX
        inc dword ptr -8[EBP]
        jmp short   L18
L38:    xor EAX,EAX
        pop EDI
        pop EBX
        leave
        ret

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