• Matthew Dempsky's avatar
    cmd/6c: Improve peep hole optimization of rotate and shift instructions. · 41ec481a
    Matthew Dempsky authored
    Update #4629.
    
    $ cat shift2.c
    unsigned int
    shift(unsigned int x, unsigned int y)
    {
            x = (x << 3);
            y = (y << 5);
            x = (x << 7);
            y = (y << 9);
            return x ^ y;
    }
    
    ## BEFORE
    $ go tool 6c -S shift2.c
    (shift2.c:2)	TEXT	shift+0(SB),$0-8
    (shift2.c:4)	MOVL	x+0(FP),!!AX
    (shift2.c:4)	SALL	$3,!!AX
    (shift2.c:4)	MOVL	AX,!!DX
    (shift2.c:5)	MOVL	y+4(FP),!!AX
    (shift2.c:5)	SALL	$5,!!AX
    (shift2.c:5)	MOVL	AX,!!CX
    (shift2.c:6)	MOVL	DX,!!AX
    (shift2.c:6)	SALL	$7,!!AX
    (shift2.c:6)	MOVL	AX,!!DX
    (shift2.c:7)	MOVL	CX,!!AX
    (shift2.c:7)	SALL	$9,!!AX
    (shift2.c:7)	MOVL	AX,!!CX
    (shift2.c:8)	MOVL	DX,!!AX
    (shift2.c:8)	XORL	CX,!!AX
    (shift2.c:8)	RET	,!!
    (shift2.c:8)	RET	,!!
    (shift2.c:8)	END	,!!
    
    ## AFTER
    $ go tool 6c -S shift2.c
    (shift2.c:2)	TEXT	shift+0(SB),$0-8
    (shift2.c:4)	MOVL	x+0(FP),!!AX
    (shift2.c:4)	SALL	$3,!!AX
    (shift2.c:5)	MOVL	y+4(FP),!!CX
    (shift2.c:5)	SALL	$5,!!CX
    (shift2.c:6)	SALL	$7,!!AX
    (shift2.c:7)	SALL	$9,!!CX
    (shift2.c:8)	XORL	CX,!!AX
    (shift2.c:8)	RET	,!!
    (shift2.c:8)	RET	,!!
    (shift2.c:8)	END	,!!
    
    R=rsc, minux.ma, dave, nigeltao
    CC=golang-dev
    https://golang.org/cl/7066055
    41ec481a
peep.c 22 KB