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cmd/internal/obj/arm64: improve arm64 wrapper prologue

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Improve static branch prediction in arm64 wrapper prologue
by making the unusual case branch forwards. (Most other
architectures implement this optimization.)

Additionally, replace a CMP+BNE pair with a CBNZ
to save one instruction.

Change-Id: Id970038b34b4aaec18c101d62e2ee00f3e32a761
Reviewed-on: https://go-review.googlesource.com/54070
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
ph 2017-08-08 23:05:17 +00:00 committed by Cherry Zhang
parent e6cbf98d69
commit 4282ba0a65
1 changed files with 48 additions and 32 deletions
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70
src/cmd/internal/obj/arm64/obj7.go
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@ -515,7 +515,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q = p
}
var q2 *obj.Prog
var retjmp *obj.LSym
for p := c.cursym.Func.Text; p != nil; p = p.Link {
o := p.As
@ -619,21 +618,24 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
// if(g->panic != nil && g->panic->argp == FP) g->panic->argp = bottom-of-frame
//
// MOV g_panic(g), R1
// CMP ZR, R1
// BEQ end
// CBNZ checkargp
// end:
// NOP
// ... function body ...
// checkargp:
// MOV panic_argp(R1), R2
// ADD $(autosize+8), RSP, R3
// CMP R2, R3
// BNE end
// ADD $8, RSP, R4
// MOVD R4, panic_argp(R1)
// end:
// NOP
// B end
//
// The NOP is needed to give the jumps somewhere to land.
// It is a liblink NOP, not a ARM64 NOP: it encodes to 0 instruction bytes.
q = q1
// MOV g_panic(g), R1
q = obj.Appendp(q, c.newprog)
q.As = AMOVD
q.From.Type = obj.TYPE_MEM
@ -642,26 +644,36 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q.To.Type = obj.TYPE_REG
q.To.Reg = REG_R1
q = obj.Appendp(q, c.newprog)
q.As = ACMP
q.From.Type = obj.TYPE_REG
q.From.Reg = REGZERO
q.Reg = REG_R1
// CBNZ R1, checkargp
cbnz := obj.Appendp(q, c.newprog)
cbnz.As = ACBNZ
cbnz.From.Type = obj.TYPE_REG
cbnz.From.Reg = REG_R1
cbnz.To.Type = obj.TYPE_BRANCH
q = obj.Appendp(q, c.newprog)
q.As = ABEQ
q.To.Type = obj.TYPE_BRANCH
q1 = q
// Empty branch target at the top of the function body
end := obj.Appendp(cbnz, c.newprog)
end.As = obj.ANOP
q = obj.Appendp(q, c.newprog)
q.As = AMOVD
q.From.Type = obj.TYPE_MEM
q.From.Reg = REG_R1
q.From.Offset = 0 // Panic.argp
q.To.Type = obj.TYPE_REG
q.To.Reg = REG_R2
// find the end of the function
var last *obj.Prog
for last = end; last.Link != nil; last = last.Link {
}
q = obj.Appendp(q, c.newprog)
// MOV panic_argp(R1), R2
mov := obj.Appendp(last, c.newprog)
mov.As = AMOVD
mov.From.Type = obj.TYPE_MEM
mov.From.Reg = REG_R1
mov.From.Offset = 0 // Panic.argp
mov.To.Type = obj.TYPE_REG
mov.To.Reg = REG_R2
// CBNZ branches to the MOV above
cbnz.Pcond = mov
// ADD $(autosize+8), SP, R3
q = obj.Appendp(mov, c.newprog)
q.As = AADD
q.From.Type = obj.TYPE_CONST
q.From.Offset = int64(c.autosize) + 8
@ -669,17 +681,20 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q.To.Type = obj.TYPE_REG
q.To.Reg = REG_R3
// CMP R2, R3
q = obj.Appendp(q, c.newprog)
q.As = ACMP
q.From.Type = obj.TYPE_REG
q.From.Reg = REG_R2
q.Reg = REG_R3
// BNE end
q = obj.Appendp(q, c.newprog)
q.As = ABNE
q.To.Type = obj.TYPE_BRANCH
q2 = q
q.Pcond = end
// ADD $8, SP, R4
q = obj.Appendp(q, c.newprog)
q.As = AADD
q.From.Type = obj.TYPE_CONST
@ -688,6 +703,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q.To.Type = obj.TYPE_REG
q.To.Reg = REG_R4
// MOV R4, panic_argp(R1)
q = obj.Appendp(q, c.newprog)
q.As = AMOVD
q.From.Type = obj.TYPE_REG
@ -696,11 +712,11 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q.To.Reg = REG_R1
q.To.Offset = 0 // Panic.argp
// B end
q = obj.Appendp(q, c.newprog)
q.As = obj.ANOP
q1.Pcond = q
q2.Pcond = q
q.As = AB
q.To.Type = obj.TYPE_BRANCH
q.Pcond = end
}
case obj.ARET: