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cmd/internal/obj/ppc64: simplify huge frame prologue

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CL 307010 for ppc64.

I spent a long time trying to figure out how to use the carry bit from
ADDCCC to further simplify this (like what we do on arm64), but gave
up after I couldn't figure out how to access the carry bit without
just adding more instructions.

Change-Id: I6cad51b93616865b203cb16554f16121375aabbc
Reviewed-on: https://go-review.googlesource.com/c/go/+/307149
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Austin Clements 2021-04-02 17:20:15 -04:00
parent 2b63404ddb
commit a06b08e7d1
1 changed files with 47 additions and 62 deletions
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109
src/cmd/internal/obj/ppc64/obj9.go
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@ -1081,80 +1081,65 @@ func (c *ctxt9) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
p.From.Reg = REG_R3
p.To.Type = obj.TYPE_REG
p.To.Reg = REGSP
} else if framesize <= objabi.StackBig {
// large stack: SP-framesize < stackguard-StackSmall
// ADD $-(framesize-StackSmall), SP, R4
// CMP stackguard, R4
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.As = ACMPU
p.From.Type = obj.TYPE_REG
p.From.Reg = REG_R3
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R4
} 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.
//
// 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)), R31
// CMPU R31, R4
// large stack: SP-framesize < stackguard-StackSmall
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.
//
// CMPU SP, $(framesize-StackSmall)
// BLT label-of-call-to-morestack
if offset <= 0xffff {
p = obj.Appendp(p, c.newprog)
p.As = ACMPU
p.From.Type = obj.TYPE_REG
p.From.Reg = REGSP
p.To.Type = obj.TYPE_CONST
p.To.Offset = offset
} else {
// Constant is too big for CMPU.
p = obj.Appendp(p, c.newprog)
p.As = AMOVD
p.From.Type = obj.TYPE_CONST
p.From.Offset = offset
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R4
p = obj.Appendp(p, c.newprog)
p.As = ACMPU
p.From.Type = obj.TYPE_REG
p.From.Reg = REGSP
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R4
}
p = obj.Appendp(p, c.newprog)
q = p
p.As = ABLT
p.To.Type = obj.TYPE_BRANCH
}
// Check against the stack guard. We've ensured this won't underflow.
// ADD $-(framesize-StackSmall), SP, R4
// CMPU stackguard, R4
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.From.Offset = -offset
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
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.To.Type = obj.TYPE_REG
p.To.Reg = REGTMP
p = obj.Appendp(p, c.newprog)
p.As = ACMPU
p.From.Type = obj.TYPE_REG
p.From.Reg = REGTMP
p.From.Reg = REG_R3
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R4
}