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cmd/internal/obj/arm: improve static branch prediction for wrapper prologue
This is a follow-up to CL 36893. Move the unlikely branch in the wrapper prologue to the end of the function, where it has minimal impact on the instruction cache. Static branch prediction is also less likely to choose a forward branch. Updates #19042 sort benchmarks: name old time/op new time/op delta SearchWrappers-4 1.44µs ± 0% 1.45µs ± 0% +1.15% (p=0.000 n=9+10) SortString1K-4 1.02ms ± 0% 1.04ms ± 0% +2.39% (p=0.000 n=10+10) SortString1K_Slice-4 960µs ± 0% 989µs ± 0% +2.95% (p=0.000 n=9+10) StableString1K-4 218µs ± 0% 213µs ± 0% -2.13% (p=0.000 n=10+10) SortInt1K-4 541µs ± 0% 543µs ± 0% +0.30% (p=0.003 n=9+10) StableInt1K-4 760µs ± 1% 763µs ± 1% +0.38% (p=0.011 n=10+10) StableInt1K_Slice-4 840µs ± 1% 779µs ± 0% -7.31% (p=0.000 n=9+10) SortInt64K-4 55.2ms ± 0% 55.4ms ± 1% +0.34% (p=0.012 n=10+8) SortInt64K_Slice-4 56.2ms ± 0% 55.6ms ± 1% -1.16% (p=0.000 n=10+10) StableInt64K-4 70.9ms ± 1% 71.0ms ± 0% ~ (p=0.315 n=10+7) Sort1e2-4 250µs ± 0% 249µs ± 1% ~ (p=0.315 n=9+10) Stable1e2-4 600µs ± 0% 594µs ± 0% -1.09% (p=0.000 n=9+10) Sort1e4-4 51.2ms ± 0% 51.4ms ± 1% +0.40% (p=0.001 n=9+10) Stable1e4-4 204ms ± 1% 199ms ± 1% -2.27% (p=0.000 n=10+10) Sort1e6-4 8.42s ± 0% 8.44s ± 0% +0.28% (p=0.000 n=8+9) Stable1e6-4 43.3s ± 0% 42.5s ± 1% -1.89% (p=0.000 n=9+9) Change-Id: I827559aa557fdba211a38ce3f77137b471c5c67e Reviewed-on: https://go-review.googlesource.com/37611 Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com> Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
This commit is contained in:
Philip Hofer
Josh Bleecher Snyder
parent
a2cc8b20fd
commit
a143f5d646
@ -341,8 +341,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
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q = p
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}
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var p1 *obj.Prog
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var p2 *obj.Prog
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var q2 *obj.Prog
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for p := cursym.Text; p != nil; p = p.Link {
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o := p.As
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@ -392,21 +390,23 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
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//
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// MOVW g_panic(g), R1
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// CMP $0, R1
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// B.EQ end
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// B.NE checkargp
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// end:
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// NOP
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// ... function ...
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// checkargp:
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// MOVW panic_argp(R1), R2
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// ADD $(autosize+4), R13, R3
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// CMP R2, R3
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// B.NE end
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// ADD $4, R13, R4
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// MOVW R4, panic_argp(R1)
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// end:
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// NOP
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// B end
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//
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// The NOP is needed to give the jumps somewhere to land.
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// It is a liblink NOP, not an ARM NOP: it encodes to 0 instruction bytes.
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p = obj.Appendp(ctxt, p)
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p.As = AMOVW
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p.From.Type = obj.TYPE_MEM
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p.From.Reg = REGG
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@ -420,20 +420,34 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
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p.From.Offset = 0
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p.Reg = REG_R1
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p = obj.Appendp(ctxt, p)
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p.As = ABEQ
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p.To.Type = obj.TYPE_BRANCH
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p1 = p
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// B.NE checkargp
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bne := obj.Appendp(ctxt, p)
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bne.As = ABNE
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bne.To.Type = obj.TYPE_BRANCH
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p = obj.Appendp(ctxt, p)
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p.As = AMOVW
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p.From.Type = obj.TYPE_MEM
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p.From.Reg = REG_R1
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p.From.Offset = 0 // Panic.argp
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R2
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// end: NOP
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end := obj.Appendp(ctxt, bne)
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end.As = obj.ANOP
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p = obj.Appendp(ctxt, p)
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// find end of function
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var last *obj.Prog
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for last = end; last.Link != nil; last = last.Link {
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}
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// MOVW panic_argp(R1), R2
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mov := obj.Appendp(ctxt, last)
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mov.As = AMOVW
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mov.From.Type = obj.TYPE_MEM
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mov.From.Reg = REG_R1
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mov.From.Offset = 0 // Panic.argp
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mov.To.Type = obj.TYPE_REG
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mov.To.Reg = REG_R2
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// B.NE branch target is MOVW above
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bne.Pcond = mov
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// ADD $(autosize+4), R13, R3
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p = obj.Appendp(ctxt, mov)
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p.As = AADD
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p.From.Type = obj.TYPE_CONST
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p.From.Offset = int64(autosize) + 4
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@ -441,17 +455,20 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R3
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// CMP R2, R3
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p = obj.Appendp(ctxt, p)
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p.As = ACMP
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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_R3
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// B.NE end
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p = obj.Appendp(ctxt, p)
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p.As = ABNE
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p.To.Type = obj.TYPE_BRANCH
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p2 = p
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p.Pcond = end
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// ADD $4, R13, R4
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p = obj.Appendp(ctxt, p)
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p.As = AADD
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p.From.Type = obj.TYPE_CONST
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@ -460,6 +477,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
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p.To.Type = obj.TYPE_REG
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p.To.Reg = REG_R4
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// MOVW R4, panic_argp(R1)
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p = obj.Appendp(ctxt, p)
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p.As = AMOVW
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p.From.Type = obj.TYPE_REG
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@ -468,11 +486,14 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
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p.To.Reg = REG_R1
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p.To.Offset = 0 // Panic.argp
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// B end
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p = obj.Appendp(ctxt, p)
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p.As = AB
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p.To.Type = obj.TYPE_BRANCH
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p.Pcond = end
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p.As = obj.ANOP
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p1.Pcond = p
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p2.Pcond = p
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// reset for subsequent passes
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p = end
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}
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case obj.ARET:
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