[sdcc-devel] [ sdcc-Feature Requests-1307995 ] Optimize divisons by powers of two.

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Feature Requests item #1307995, was opened at 2005-09-29 15:37
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Category: None
Group: None
Status: Open
Priority: 5
Submitted By: Philipp Krause (spth)
Assigned to: Nobody/Anonymous (nobody)
Summary: Optimize divisons by powers of two.

Initial Comment:
Please optimize divisons by powers of two.
The following two simple functions now generate calls
to the internal division functions, while they could be
easily implemented with bit shifts:

C code:

int divtesti(int a)
{
	return(a / 8);
}

char divtestc(char a)
{
	return(a / 8);
}

Resulting Z80 asm:
;test.c:8: int divtesti(int a)
;       genLabel
;       genFunction
;       ---------------------------------
; Function divtesti
; ---------------------------------
_divtesti_start::
_divtesti:
        push    ix
        ld      ix,#0
        add     ix,sp
;test.c:10: return(a / 8);
;       genIpush
; _saveRegsForCall: sendSetSize: 0 deInUse: 0 bcInUse:
0 deSending: 0
        ld      hl,#0x0008
        push    hl
;       genIpush
;       AOP_STK for
        ld      l,4(ix)
        ld      h,5(ix)
        push    hl
;       genCall
        call    __divsint_rrx_s
        ld      b,h
        ld      c,l
        pop     af
        pop     af
;       genRet
; Dump of IC_LEFT: type AOP_REG size 2
;        reg = bc
        ld      l,c
        ld      h,b
;       genLabel
00101$:
;       genEndFunction
        pop     ix
        ret
_divtesti_end::
_BILD:
        .dw #0x1800
;test.c:13: char divtestc(char a)
;       genLabel
;       genFunction
;       ---------------------------------
; Function divtestc
; ---------------------------------
_divtestc_start::
_divtestc:
        push    ix
        ld      ix,#0
        add     ix,sp
;test.c:15: return(a / 8);
;       genIpush
; _saveRegsForCall: sendSetSize: 0 deInUse: 0 bcInUse:
0 deSending: 0
        ld      a,#0x08
        push    af
        inc     sp
;       genIpush
;       AOP_STK for
        ld      a,4(ix)
        push    af
        inc     sp
;       genCall
        call    __divschar_rrx_s
        ld      c,l
        pop     af
;       genRet
; Dump of IC_LEFT: type AOP_REG size 1
;        reg = c
        ld      l,c
;       genLabel
00101$:
;       genEndFunction
        pop     ix
        ret
_divtestc_end::


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