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cmd/internal/obj/mips: simplify huge frame prologue
CL 307010 for mips. Change-Id: Ie9addea728548315fdbb8e46f75da4010a9796bb Reviewed-on: https://go-review.googlesource.com/c/go/+/307051 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>
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@ -648,16 +648,14 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
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}
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func (c *ctxt0) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
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var mov, add, sub obj.As
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var mov, add obj.As
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if c.ctxt.Arch.Family == sys.MIPS64 {
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add = AADDV
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mov = AMOVV
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sub = ASUBVU
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} else {
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add = AADDU
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mov = AMOVW
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sub = ASUBU
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}
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// MOV g_stackguard(g), R1
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@ -691,81 +689,49 @@ func (c *ctxt0) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
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p.Reg = REG_R1
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R1
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} else if framesize <= objabi.StackBig {
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} else {
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// large stack: SP-framesize < stackguard-StackSmall
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offset := int64(framesize) - objabi.StackSmall
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if framesize > objabi.StackBig {
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// Such a large stack we need to protect against underflow.
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// The runtime guarantees SP > objabi.StackBig, but
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// framesize is large enough that SP-framesize may
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// underflow, causing a direct comparison with the
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// stack guard to incorrectly succeed. We explicitly
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// guard against underflow.
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//
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// SGTU $(framesize-StackSmall), SP, R2
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// BNE R2, label-of-call-to-morestack
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p = obj.Appendp(p, c.newprog)
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p.As = ASGTU
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p.From.Type = obj.TYPE_CONST
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p.From.Offset = offset
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p.Reg = REGSP
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R2
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p = obj.Appendp(p, c.newprog)
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q = p
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p.As = ABNE
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p.From.Type = obj.TYPE_REG
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p.From.Reg = REG_R2
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p.To.Type = obj.TYPE_BRANCH
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p.Mark |= BRANCH
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}
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// Check against the stack guard. We've ensured this won't underflow.
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// ADD $-(framesize-StackSmall), SP, R2
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// SGTU R2, stackguard, R1
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p = obj.Appendp(p, c.newprog)
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p.As = add
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p.From.Type = obj.TYPE_CONST
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p.From.Offset = -(int64(framesize) - objabi.StackSmall)
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p.From.Offset = -offset
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p.Reg = REGSP
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R2
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p = obj.Appendp(p, c.newprog)
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p.As = ASGTU
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p.From.Type = obj.TYPE_REG
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p.From.Reg = REG_R2
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p.Reg = REG_R1
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R1
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} else {
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// Such a large stack we need to protect against wraparound.
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// If SP is close to zero:
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// SP-stackguard+StackGuard <= framesize + (StackGuard-StackSmall)
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// The +StackGuard on both sides is required to keep the left side positive:
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// SP is allowed to be slightly below stackguard. See stack.h.
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//
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// Preemption sets stackguard to StackPreempt, a very large value.
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// That breaks the math above, so we have to check for that explicitly.
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// // stackguard is R1
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// MOV $StackPreempt, R2
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// BEQ R1, R2, label-of-call-to-morestack
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// ADD $StackGuard, SP, R2
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// SUB R1, R2
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// MOV $(framesize+(StackGuard-StackSmall)), R1
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// SGTU R2, R1, R1
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p = obj.Appendp(p, c.newprog)
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p.As = mov
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p.From.Type = obj.TYPE_CONST
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p.From.Offset = objabi.StackPreempt
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R2
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p = obj.Appendp(p, c.newprog)
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q = p
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p.As = ABEQ
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p.From.Type = obj.TYPE_REG
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p.From.Reg = REG_R1
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p.Reg = REG_R2
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p.To.Type = obj.TYPE_BRANCH
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p.Mark |= BRANCH
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p = obj.Appendp(p, c.newprog)
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p.As = add
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p.From.Type = obj.TYPE_CONST
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p.From.Offset = int64(objabi.StackGuard)
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p.Reg = REGSP
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R2
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p = obj.Appendp(p, c.newprog)
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p.As = sub
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p.From.Type = obj.TYPE_REG
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p.From.Reg = REG_R1
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R2
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p = obj.Appendp(p, c.newprog)
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p.As = mov
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p.From.Type = obj.TYPE_CONST
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p.From.Offset = int64(framesize) + int64(objabi.StackGuard) - objabi.StackSmall
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R1
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p = obj.Appendp(p, c.newprog)
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p.As = ASGTU
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p.From.Type = obj.TYPE_REG
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