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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
// zerorange clears the stack in the given range.
func zerorange(pp *gc.Progs, p *obj.Prog, off, cnt int64, _ *uint32) *obj.Prog {
if cnt == 0 {
return p
}
// Adjust the frame to account for LR.
off += gc.Ctxt.FixedFrameSize()
reg := int16(s390x.REGSP)
// If the off 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 off < 0 || off > 4096-clearLoopCutoff || cnt > clearLoopCutoff {
p = pp.Appendpp(p, s390x.AADD, obj.TYPE_CONST, 0, off, obj.TYPE_REG, s390x.REGRT1, 0)
p.Reg = int16(s390x.REGSP)
reg = s390x.REGRT1
off = 0
}
// Generate a loop of large clears.
if cnt > clearLoopCutoff {
ireg := int16(s390x.REGRT2) // register holds number of remaining loop iterations
p = pp.Appendpp(p, s390x.AMOVD, obj.TYPE_CONST, 0, cnt/256, obj.TYPE_REG, ireg, 0)
p = pp.Appendpp(p, s390x.ACLEAR, obj.TYPE_CONST, 0, 256, obj.TYPE_MEM, reg, off)
pl := p
p = pp.Appendpp(p, s390x.AADD, obj.TYPE_CONST, 0, 256, obj.TYPE_REG, reg, 0)
p = pp.Appendpp(p, s390x.ABRCTG, obj.TYPE_REG, ireg, 0, obj.TYPE_BRANCH, 0, 0)
gc.Patch(p, pl)
cnt = cnt % 256
}
// 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 = pp.Appendpp(p, ins, obj.TYPE_CONST, 0, 0, obj.TYPE_MEM, reg, off)
// Handle clears that would require multiple move instructions with CLEAR (assembled as XC).
default:
p = pp.Appendpp(p, s390x.ACLEAR, obj.TYPE_CONST, 0, n, obj.TYPE_MEM, reg, off)
}
cnt -= n
off += n
}
return p
}
func ginsnop(pp *gc.Progs) *obj.Prog {
return pp.Prog(s390x.ANOPH)
}
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