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cmd/internal/obj/s390x: simplify huge frame prologue

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CL 307010 for s390x.

Change-Id: I43e1f93dd01c814417f8ef7480aa82c05b2b6b66
Reviewed-on: https://go-review.googlesource.com/c/go/+/307151
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Austin Clements 2021-04-02 17:20:15 -04:00
parent 042f4cbb6f
commit 191167c2b2
1 changed files with 37 additions and 67 deletions
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104
src/cmd/internal/obj/s390x/objz.go
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@ -568,7 +568,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
}
func (c *ctxtz) stacksplitPre(p *obj.Prog, framesize int32) (*obj.Prog, *obj.Prog) {
var q *obj.Prog
// MOVD g_stackguard(g), R3
p = obj.Appendp(p, c.newprog)
@ -589,97 +588,68 @@ func (c *ctxtz) stacksplitPre(p *obj.Prog, framesize int32) (*obj.Prog, *obj.Pro
// unnecessarily. See issue #35470.
p = c.ctxt.StartUnsafePoint(p, c.newprog)
q = nil
if framesize <= objabi.StackSmall {
// small stack: SP < stackguard
// CMPUBGE stackguard, SP, label-of-call-to-morestack
p = obj.Appendp(p, c.newprog)
//q1 = p
p.From.Type = obj.TYPE_REG
p.From.Reg = REG_R3
p.Reg = REGSP
p.As = ACMPUBGE
p.To.Type = obj.TYPE_BRANCH
} else if framesize <= objabi.StackBig {
return p, nil
}
// large stack: SP-framesize < stackguard-StackSmall
// ADD $-(framesize-StackSmall), SP, R4
// CMPUBGE stackguard, R4, label-of-call-to-morestack
p = obj.Appendp(p, c.newprog)
p.As = AADD
p.From.Type = obj.TYPE_CONST
p.From.Offset = -(int64(framesize) - objabi.StackSmall)
p.Reg = REGSP
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R4
p = obj.Appendp(p, c.newprog)
p.From.Type = obj.TYPE_REG
p.From.Reg = REG_R3
p.Reg = REG_R4
p.As = ACMPUBGE
p.To.Type = obj.TYPE_BRANCH
} else {
// Such a large stack we need to protect against wraparound.
// If SP is close to zero:
// SP-stackguard+StackGuard <= framesize + (StackGuard-StackSmall)
// The +StackGuard on both sides is required to keep the left side positive:
// SP is allowed to be slightly below stackguard. See stack.h.
var q *obj.Prog
offset := int64(framesize) - objabi.StackSmall
if framesize > objabi.StackBig {
// Such a large stack we need to protect against underflow.
// The runtime guarantees SP > objabi.StackBig, but
// framesize is large enough that SP-framesize may
// underflow, causing a direct comparison with the
// stack guard to incorrectly succeed. We explicitly
// guard against underflow.
//
// Preemption sets stackguard to StackPreempt, a very large value.
// That breaks the math above, so we have to check for that explicitly.
// // stackguard is R3
// CMP R3, $StackPreempt
// BEQ label-of-call-to-morestack
// ADD $StackGuard, SP, R4
// SUB R3, R4
// MOVD $(framesize+(StackGuard-StackSmall)), TEMP
// CMPUBGE TEMP, R4, label-of-call-to-morestack
p = obj.Appendp(p, c.newprog)
p.As = ACMP
p.From.Type = obj.TYPE_REG
p.From.Reg = REG_R3
p.To.Type = obj.TYPE_CONST
p.To.Offset = objabi.StackPreempt
p = obj.Appendp(p, c.newprog)
q = p
p.As = ABEQ
p.To.Type = obj.TYPE_BRANCH
p = obj.Appendp(p, c.newprog)
p.As = AADD
p.From.Type = obj.TYPE_CONST
p.From.Offset = int64(objabi.StackGuard)
p.Reg = REGSP
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R4
p = obj.Appendp(p, c.newprog)
p.As = ASUB
p.From.Type = obj.TYPE_REG
p.From.Reg = REG_R3
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R4
// MOVD $(framesize-StackSmall), R4
// CMPUBLT SP, R4, label-of-call-to-morestack
p = obj.Appendp(p, c.newprog)
p.As = AMOVD
p.From.Type = obj.TYPE_CONST
p.From.Offset = int64(framesize) + int64(objabi.StackGuard) - objabi.StackSmall
p.From.Offset = offset
p.To.Type = obj.TYPE_REG
p.To.Reg = REGTMP
p.To.Reg = REG_R4
p = obj.Appendp(p, c.newprog)
q = p
p.As = ACMPUBLT
p.From.Type = obj.TYPE_REG
p.From.Reg = REGSP
p.Reg = REG_R4
p.To.Type = obj.TYPE_BRANCH
}
// Check against the stack guard. We've ensured this won't underflow.
// ADD $-(framesize-StackSmall), SP, R4
// CMPUBGE stackguard, R4, label-of-call-to-morestack
p = obj.Appendp(p, c.newprog)
p.As = AADD
p.From.Type = obj.TYPE_CONST
p.From.Offset = -offset
p.Reg = REGSP
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R4
p = obj.Appendp(p, c.newprog)
p.From.Type = obj.TYPE_REG
p.From.Reg = REGTMP
p.From.Reg = REG_R3
p.Reg = REG_R4
p.As = ACMPUBGE
p.To.Type = obj.TYPE_BRANCH
}
return p, q
}