From a143f5d646e5e6a835f70235ee5e604deda5f3be Mon Sep 17 00:00:00 2001 From: Philip Hofer Date: Tue, 28 Feb 2017 14:35:37 -0800 Subject: [PATCH] cmd/internal/obj/arm: improve static branch prediction for wrapper prologue MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Josh Bleecher Snyder --- src/cmd/internal/obj/arm/obj5.go | 83 ++++++++++++++++++++------------ 1 file changed, 52 insertions(+), 31 deletions(-) diff --git a/src/cmd/internal/obj/arm/obj5.go b/src/cmd/internal/obj/arm/obj5.go index 75d22bcf81..52a17e9fd8 100644 --- a/src/cmd/internal/obj/arm/obj5.go +++ b/src/cmd/internal/obj/arm/obj5.go @@ -341,8 +341,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) { q = p } - var p1 *obj.Prog - var p2 *obj.Prog var q2 *obj.Prog for p := cursym.Text; p != nil; p = p.Link { o := p.As @@ -391,22 +389,24 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) { // if(g->panic != nil && g->panic->argp == FP) g->panic->argp = bottom-of-frame // // MOVW g_panic(g), R1 - // CMP $0, R1 - // B.EQ end - // MOVW panic_argp(R1), R2 - // ADD $(autosize+4), R13, R3 - // CMP R2, R3 - // B.NE end - // ADD $4, R13, R4 - // MOVW R4, panic_argp(R1) + // CMP $0, R1 + // B.NE checkargp // end: // NOP + // ... function ... + // checkargp: + // MOVW panic_argp(R1), R2 + // ADD $(autosize+4), R13, R3 + // CMP R2, R3 + // B.NE end + // ADD $4, R13, R4 + // MOVW R4, panic_argp(R1) + // B end // // The NOP is needed to give the jumps somewhere to land. // It is a liblink NOP, not an ARM NOP: it encodes to 0 instruction bytes. p = obj.Appendp(ctxt, p) - p.As = AMOVW p.From.Type = obj.TYPE_MEM p.From.Reg = REGG @@ -420,20 +420,34 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) { p.From.Offset = 0 p.Reg = REG_R1 - p = obj.Appendp(ctxt, p) - p.As = ABEQ - p.To.Type = obj.TYPE_BRANCH - p1 = p + // B.NE checkargp + bne := obj.Appendp(ctxt, p) + bne.As = ABNE + bne.To.Type = obj.TYPE_BRANCH - p = obj.Appendp(ctxt, p) - p.As = AMOVW - p.From.Type = obj.TYPE_MEM - p.From.Reg = REG_R1 - p.From.Offset = 0 // Panic.argp - p.To.Type = obj.TYPE_REG - p.To.Reg = REG_R2 + // end: NOP + end := obj.Appendp(ctxt, bne) + end.As = obj.ANOP - p = obj.Appendp(ctxt, p) + // find end of function + var last *obj.Prog + for last = end; last.Link != nil; last = last.Link { + } + + // MOVW panic_argp(R1), R2 + mov := obj.Appendp(ctxt, last) + mov.As = AMOVW + 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 + + // B.NE branch target is MOVW above + bne.Pcond = mov + + // ADD $(autosize+4), R13, R3 + p = obj.Appendp(ctxt, mov) p.As = AADD p.From.Type = obj.TYPE_CONST p.From.Offset = int64(autosize) + 4 @@ -441,17 +455,20 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) { p.To.Type = obj.TYPE_REG p.To.Reg = REG_R3 + // CMP R2, R3 p = obj.Appendp(ctxt, p) p.As = ACMP p.From.Type = obj.TYPE_REG p.From.Reg = REG_R2 p.Reg = REG_R3 + // B.NE end p = obj.Appendp(ctxt, p) p.As = ABNE p.To.Type = obj.TYPE_BRANCH - p2 = p + p.Pcond = end + // ADD $4, R13, R4 p = obj.Appendp(ctxt, p) p.As = AADD p.From.Type = obj.TYPE_CONST @@ -460,6 +477,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) { p.To.Type = obj.TYPE_REG p.To.Reg = REG_R4 + // MOVW R4, panic_argp(R1) p = obj.Appendp(ctxt, p) p.As = AMOVW p.From.Type = obj.TYPE_REG @@ -468,11 +486,14 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) { p.To.Reg = REG_R1 p.To.Offset = 0 // Panic.argp + // B end p = obj.Appendp(ctxt, p) + p.As = AB + p.To.Type = obj.TYPE_BRANCH + p.Pcond = end - p.As = obj.ANOP - p1.Pcond = p - p2.Pcond = p + // reset for subsequent passes + p = end } case obj.ARET: @@ -702,7 +723,7 @@ func softfloat(ctxt *obj.Link, cursym *obj.LSym) { } func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32) *obj.Prog { - // MOVW g_stackguard(g), R1 + // MOVW g_stackguard(g), R1 p = obj.Appendp(ctxt, p) p.As = AMOVW @@ -748,11 +769,11 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32) *obj.Prog { // 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. - // CMP $StackPreempt, R1 + // CMP $StackPreempt, R1 // MOVW.NE $StackGuard(SP), R2 - // SUB.NE R1, R2 + // SUB.NE R1, R2 // MOVW.NE $(framesize+(StackGuard-StackSmall)), R3 - // CMP.NE R3, R2 + // CMP.NE R3, R2 p = obj.Appendp(ctxt, p) p.As = ACMP