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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package s390x
import (
"cmd/compile/internal/gc"
"cmd/internal/obj"
"cmd/internal/obj/s390x"
)
// clearLoopCutOff is the (somewhat arbitrary) value above which it is better
// to have a loop of clear instructions (e.g. XCs) rather than just generating
// multiple instructions (i.e. loop unrolling).
// Must be between 256 and 4096.
const clearLoopCutoff = 1024
func defframe(ptxt *obj.Prog) {
// fill in argument size, stack size
ptxt.To.Type = obj.TYPE_TEXTSIZE
ptxt.To.Val = int32(gc.Rnd(gc.Curfn.Type.ArgWidth(), int64(gc.Widthptr)))
frame := uint32(gc.Rnd(gc.Stksize+gc.Maxarg, int64(gc.Widthreg)))
ptxt.To.Offset = int64(frame)
// insert code to zero ambiguously live variables
// so that the garbage collector only sees initialized values
// when it looks for pointers.
p := ptxt
hi := int64(0)
lo := hi
// iterate through declarations - they are sorted in decreasing xoffset order.
for _, n := range gc.Curfn.Func.Dcl {
if !n.Name.Needzero {
continue
}
if n.Class != gc.PAUTO {
gc.Fatalf("needzero class %d", n.Class)
}
if n.Type.Width%int64(gc.Widthptr) != 0 || n.Xoffset%int64(gc.Widthptr) != 0 || n.Type.Width == 0 {
gc.Fatalf("var %L has size %d offset %d", n, int(n.Type.Width), int(n.Xoffset))
}
if lo != hi && n.Xoffset+n.Type.Width >= lo-int64(2*gc.Widthreg) {
// merge with range we already have
lo = n.Xoffset
continue
}
// zero old range
p = zerorange(p, int64(frame), lo, hi)
// set new range
hi = n.Xoffset + n.Type.Width
lo = n.Xoffset
}
// zero final range
zerorange(p, int64(frame), lo, hi)
}
// zerorange clears the stack in the given range.
func zerorange(p *obj.Prog, frame int64, lo int64, hi int64) *obj.Prog {
cnt := hi - lo
if cnt == 0 {
return p
}
// Adjust the frame to account for LR.
frame += gc.Ctxt.FixedFrameSize()
offset := frame + lo
reg := int16(s390x.REGSP)
// If the offset cannot fit in a 12-bit unsigned displacement then we
// need to create a copy of the stack pointer that we can adjust.
// We also need to do this if we are going to loop.
if offset < 0 || offset > 4096-clearLoopCutoff || cnt > clearLoopCutoff {
p = gc.Appendpp(p, s390x.AADD, obj.TYPE_CONST, 0, offset, obj.TYPE_REG, s390x.REGRT1, 0)
p.Reg = int16(s390x.REGSP)
reg = s390x.REGRT1
offset = 0
}
// Generate a loop of large clears.
if cnt > clearLoopCutoff {
n := cnt - (cnt % 256)
end := int16(s390x.REGRT2)
p = gc.Appendpp(p, s390x.AADD, obj.TYPE_CONST, 0, offset+n, obj.TYPE_REG, end, 0)
p.Reg = reg
p = gc.Appendpp(p, s390x.AXC, obj.TYPE_MEM, reg, offset, obj.TYPE_MEM, reg, offset)
p.From3 = new(obj.Addr)
p.From3.Type = obj.TYPE_CONST
p.From3.Offset = 256
pl := p
p = gc.Appendpp(p, s390x.AADD, obj.TYPE_CONST, 0, 256, obj.TYPE_REG, reg, 0)
p = gc.Appendpp(p, s390x.ACMP, obj.TYPE_REG, reg, 0, obj.TYPE_REG, end, 0)
p = gc.Appendpp(p, s390x.ABNE, obj.TYPE_NONE, 0, 0, obj.TYPE_BRANCH, 0, 0)
gc.Patch(p, pl)
cnt -= n
}
// Generate remaining clear instructions without a loop.
for cnt > 0 {
n := cnt
// Can clear at most 256 bytes per instruction.
if n > 256 {
n = 256
}
switch n {
// Handle very small clears with move instructions.
case 8, 4, 2, 1:
ins := s390x.AMOVB
switch n {
case 8:
ins = s390x.AMOVD
case 4:
ins = s390x.AMOVW
case 2:
ins = s390x.AMOVH
}
p = gc.Appendpp(p, ins, obj.TYPE_CONST, 0, 0, obj.TYPE_MEM, reg, offset)
// Handle clears that would require multiple move instructions with XC.
default:
p = gc.Appendpp(p, s390x.AXC, obj.TYPE_MEM, reg, offset, obj.TYPE_MEM, reg, offset)
p.From3 = new(obj.Addr)
p.From3.Type = obj.TYPE_CONST
p.From3.Offset = n
}
cnt -= n
offset += n
}
return p
}
func zeroAuto(n *gc.Node, pp *obj.Prog) {
// Note: this code must not clobber any registers.
p := gc.AddAsmAfter(s390x.ACLEAR, pp)
pp = p
p.From.Type = obj.TYPE_CONST
p.From.Offset = n.Type.Size()
p.To.Type = obj.TYPE_MEM
p.To.Name = obj.NAME_AUTO
p.To.Reg = s390x.REGSP
p.To.Offset = n.Xoffset
p.To.Sym = gc.Linksym(n.Sym)
}
func ginsnop() {
p := gc.Prog(s390x.AOR)
p.From.Type = obj.TYPE_REG
p.From.Reg = int16(s390x.REG_R0)
p.To.Type = obj.TYPE_REG
p.To.Reg = int16(s390x.REG_R0)
}
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