github.com/rakyll/go@v0.0.0-20170216000551-64c02460d703/src/cmd/compile/internal/x86/ggen.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package x86
     6  
     7  import (
     8  	"cmd/compile/internal/gc"
     9  	"cmd/internal/obj"
    10  	"cmd/internal/obj/x86"
    11  )
    12  
    13  func defframe(ptxt *obj.Prog) {
    14  	// fill in argument size, stack size
    15  	ptxt.To.Type = obj.TYPE_TEXTSIZE
    16  
    17  	ptxt.To.Val = int32(gc.Rnd(gc.Curfn.Type.ArgWidth(), int64(gc.Widthptr)))
    18  	frame := uint32(gc.Rnd(gc.Stksize+gc.Maxarg, int64(gc.Widthreg)))
    19  	ptxt.To.Offset = int64(frame)
    20  
    21  	// insert code to zero ambiguously live variables
    22  	// so that the garbage collector only sees initialized values
    23  	// when it looks for pointers.
    24  	p := ptxt
    25  
    26  	hi := int64(0)
    27  	lo := hi
    28  	ax := uint32(0)
    29  	for _, n := range gc.Curfn.Func.Dcl {
    30  		if !n.Name.Needzero {
    31  			continue
    32  		}
    33  		if n.Class != gc.PAUTO {
    34  			gc.Fatalf("needzero class %d", n.Class)
    35  		}
    36  		if n.Type.Width%int64(gc.Widthptr) != 0 || n.Xoffset%int64(gc.Widthptr) != 0 || n.Type.Width == 0 {
    37  			gc.Fatalf("var %L has size %d offset %d", n, int(n.Type.Width), int(n.Xoffset))
    38  		}
    39  		if lo != hi && n.Xoffset+n.Type.Width >= lo-int64(2*gc.Widthptr) {
    40  			// merge with range we already have
    41  			lo = n.Xoffset
    42  
    43  			continue
    44  		}
    45  
    46  		// zero old range
    47  		p = zerorange(p, int64(frame), lo, hi, &ax)
    48  
    49  		// set new range
    50  		hi = n.Xoffset + n.Type.Width
    51  
    52  		lo = n.Xoffset
    53  	}
    54  
    55  	// zero final range
    56  	zerorange(p, int64(frame), lo, hi, &ax)
    57  }
    58  
    59  func zerorange(p *obj.Prog, frame int64, lo int64, hi int64, ax *uint32) *obj.Prog {
    60  	cnt := hi - lo
    61  	if cnt == 0 {
    62  		return p
    63  	}
    64  	if *ax == 0 {
    65  		p = gc.Appendpp(p, x86.AMOVL, obj.TYPE_CONST, 0, 0, obj.TYPE_REG, x86.REG_AX, 0)
    66  		*ax = 1
    67  	}
    68  
    69  	if cnt <= int64(4*gc.Widthreg) {
    70  		for i := int64(0); i < cnt; i += int64(gc.Widthreg) {
    71  			p = gc.Appendpp(p, x86.AMOVL, obj.TYPE_REG, x86.REG_AX, 0, obj.TYPE_MEM, x86.REG_SP, frame+lo+i)
    72  		}
    73  	} else if !gc.Nacl && cnt <= int64(128*gc.Widthreg) {
    74  		p = gc.Appendpp(p, x86.ALEAL, obj.TYPE_MEM, x86.REG_SP, frame+lo, obj.TYPE_REG, x86.REG_DI, 0)
    75  		p = gc.Appendpp(p, obj.ADUFFZERO, obj.TYPE_NONE, 0, 0, obj.TYPE_ADDR, 0, 1*(128-cnt/int64(gc.Widthreg)))
    76  		p.To.Sym = gc.Duffzero
    77  	} else {
    78  		p = gc.Appendpp(p, x86.AMOVL, obj.TYPE_CONST, 0, cnt/int64(gc.Widthreg), obj.TYPE_REG, x86.REG_CX, 0)
    79  		p = gc.Appendpp(p, x86.ALEAL, obj.TYPE_MEM, x86.REG_SP, frame+lo, obj.TYPE_REG, x86.REG_DI, 0)
    80  		p = gc.Appendpp(p, x86.AREP, obj.TYPE_NONE, 0, 0, obj.TYPE_NONE, 0, 0)
    81  		p = gc.Appendpp(p, x86.ASTOSL, obj.TYPE_NONE, 0, 0, obj.TYPE_NONE, 0, 0)
    82  	}
    83  
    84  	return p
    85  }
    86  
    87  func ginsnop() {
    88  	p := gc.Prog(x86.AXCHGL)
    89  	p.From.Type = obj.TYPE_REG
    90  	p.From.Reg = x86.REG_AX
    91  	p.To.Type = obj.TYPE_REG
    92  	p.To.Reg = x86.REG_AX
    93  }