cmd/compile: compiler support for buffered write barrier

This CL implements the compiler support for calling the buffered write
barrier added by the previous CL.

Since the buffered write barrier is only implemented on amd64 right
now, this still supports the old, eager write barrier as well. There's
little overhead to supporting both and this way a few tests in
test/fixedbugs that expect to have liveness maps at write barrier
calls can easily opt-in to the old, eager barrier.

This significantly improves the performance of the write barrier:

name             old time/op  new time/op  delta
WriteBarrier-12  73.5ns ±20%  19.2ns ±27%  -73.90%  (p=0.000 n=19+18)

It also reduces the size of binaries because the write barrier call is
more compact:

name        old object-bytes  new object-bytes  delta
Template           398k ± 0%         393k ± 0%  -1.14%  (p=0.008 n=5+5)
Unicode            208k ± 0%         206k ± 0%  -1.00%  (p=0.008 n=5+5)
GoTypes           1.18M ± 0%        1.15M ± 0%  -2.00%  (p=0.008 n=5+5)
Compiler          4.05M ± 0%        3.88M ± 0%  -4.26%  (p=0.008 n=5+5)
SSA               8.25M ± 0%        8.11M ± 0%  -1.59%  (p=0.008 n=5+5)
Flate              228k ± 0%         224k ± 0%  -1.83%  (p=0.008 n=5+5)
GoParser           295k ± 0%         284k ± 0%  -3.62%  (p=0.008 n=5+5)
Reflect           1.00M ± 0%        0.99M ± 0%  -0.70%  (p=0.008 n=5+5)
Tar                339k ± 0%         333k ± 0%  -1.67%  (p=0.008 n=5+5)
XML                404k ± 0%         395k ± 0%  -2.10%  (p=0.008 n=5+5)
[Geo mean]         704k              690k       -2.00%

name        old exe-bytes     new exe-bytes     delta
HelloSize         1.05M ± 0%        1.04M ± 0%  -1.55%  (p=0.008 n=5+5)

https://perf.golang.org/search?q=upload:20171027.1

(Amusingly, this also reduces compiler allocations by 0.75%, which,
combined with the better write barrier, speeds up the compiler overall
by 2.10%. See the perf link.)

It slightly improves the performance of most of the go1 benchmarks and
improves the performance of the x/benchmarks:

name                      old time/op    new time/op    delta
BinaryTree17-12              2.40s ± 1%     2.47s ± 1%  +2.69%  (p=0.000 n=19+19)
Fannkuch11-12                2.95s ± 0%     2.95s ± 0%  +0.21%  (p=0.000 n=20+19)
FmtFprintfEmpty-12          41.8ns ± 4%    41.4ns ± 2%  -1.03%  (p=0.014 n=20+20)
FmtFprintfString-12         68.7ns ± 2%    67.5ns ± 1%  -1.75%  (p=0.000 n=20+17)
FmtFprintfInt-12            79.0ns ± 3%    77.1ns ± 1%  -2.40%  (p=0.000 n=19+17)
FmtFprintfIntInt-12          127ns ± 1%     123ns ± 3%  -3.42%  (p=0.000 n=20+20)
FmtFprintfPrefixedInt-12     152ns ± 1%     150ns ± 1%  -1.02%  (p=0.000 n=18+17)
FmtFprintfFloat-12           211ns ± 1%     209ns ± 0%  -0.99%  (p=0.000 n=20+16)
FmtManyArgs-12               500ns ± 0%     496ns ± 0%  -0.73%  (p=0.000 n=17+20)
GobDecode-12                6.44ms ± 1%    6.53ms ± 0%  +1.28%  (p=0.000 n=20+19)
GobEncode-12                5.46ms ± 0%    5.46ms ± 1%    ~     (p=0.550 n=19+20)
Gzip-12                      220ms ± 1%     216ms ± 0%  -1.75%  (p=0.000 n=19+19)
Gunzip-12                   38.8ms ± 0%    38.6ms ± 0%  -0.30%  (p=0.000 n=18+19)
HTTPClientServer-12         79.0µs ± 1%    78.2µs ± 1%  -1.01%  (p=0.000 n=20+20)
JSONEncode-12               11.9ms ± 0%    11.9ms ± 0%  -0.29%  (p=0.000 n=20+19)
JSONDecode-12               52.6ms ± 0%    52.2ms ± 0%  -0.68%  (p=0.000 n=19+20)
Mandelbrot200-12            3.69ms ± 0%    3.68ms ± 0%  -0.36%  (p=0.000 n=20+20)
GoParse-12                  3.13ms ± 1%    3.18ms ± 1%  +1.67%  (p=0.000 n=19+20)
RegexpMatchEasy0_32-12      73.2ns ± 1%    72.3ns ± 1%  -1.19%  (p=0.000 n=19+18)
RegexpMatchEasy0_1K-12       241ns ± 0%     239ns ± 0%  -0.83%  (p=0.000 n=17+16)
RegexpMatchEasy1_32-12      68.6ns ± 1%    69.0ns ± 1%  +0.47%  (p=0.015 n=18+16)
RegexpMatchEasy1_1K-12       364ns ± 0%     361ns ± 0%  -0.67%  (p=0.000 n=16+17)
RegexpMatchMedium_32-12      104ns ± 1%     103ns ± 1%  -0.79%  (p=0.001 n=20+15)
RegexpMatchMedium_1K-12     33.8µs ± 3%    34.0µs ± 2%    ~     (p=0.267 n=20+19)
RegexpMatchHard_32-12       1.64µs ± 1%    1.62µs ± 2%  -1.25%  (p=0.000 n=19+18)
RegexpMatchHard_1K-12       49.2µs ± 0%    48.7µs ± 1%  -0.93%  (p=0.000 n=19+18)
Revcomp-12                   391ms ± 5%     396ms ± 7%    ~     (p=0.154 n=19+19)
Template-12                 63.1ms ± 0%    59.5ms ± 0%  -5.76%  (p=0.000 n=18+19)
TimeParse-12                 307ns ± 0%     306ns ± 0%  -0.39%  (p=0.000 n=19+17)
TimeFormat-12                325ns ± 0%     323ns ± 0%  -0.50%  (p=0.000 n=19+19)
[Geo mean]                  47.3µs         46.9µs       -0.67%

https://perf.golang.org/search?q=upload:20171026.1

name                       old time/op  new time/op  delta
Garbage/benchmem-MB=64-12  2.25ms ± 1%  2.20ms ± 1%  -2.31%  (p=0.000 n=18+18)
HTTP-12                    12.6µs ± 0%  12.6µs ± 0%  -0.72%  (p=0.000 n=18+17)
JSON-12                    11.0ms ± 0%  11.0ms ± 1%  -0.68%  (p=0.000 n=17+19)

https://perf.golang.org/search?q=upload:20171026.2

Updates #14951.
Updates #22460.

Change-Id: Id4c0932890a1d41020071bec73b8522b1367d3e7
Reviewed-on: https://go-review.googlesource.com/73712
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/compile/internal/amd64/ssa.go

@@ -824,6 +824,12 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
 
+	case ssa.OpAMD64LoweredWB:
+		p := s.Prog(obj.ACALL)
+		p.To.Type = obj.TYPE_MEM
+		p.To.Name = obj.NAME_EXTERN
+		p.To.Sym = v.Aux.(*obj.LSym)
+
 	case ssa.OpAMD64NEGQ, ssa.OpAMD64NEGL,
 		ssa.OpAMD64BSWAPQ, ssa.OpAMD64BSWAPL,
 		ssa.OpAMD64NOTQ, ssa.OpAMD64NOTL:

src/cmd/compile/internal/gc/asm_test.go

@@ -468,7 +468,7 @@ var linuxAMD64Tests = []*asmTest{
 			*t = T2{}
 		}
 		`,
-		pos: []string{"\tXORPS\tX., X", "\tMOVUPS\tX., \\(.*\\)", "\tMOVQ\t\\$0, 16\\(.*\\)", "\tCALL\truntime\\.writebarrierptr\\(SB\\)"},
+		pos: []string{"\tXORPS\tX., X", "\tMOVUPS\tX., \\(.*\\)", "\tMOVQ\t\\$0, 16\\(.*\\)", "\tCALL\truntime\\.(writebarrierptr|gcWriteBarrier)\\(SB\\)"},
 	},
 	// Rotate tests
 	{

src/cmd/compile/internal/gc/go.go

@@ -287,6 +287,7 @@ var (
 	goschedguarded,
 	writeBarrier,
 	writebarrierptr,
+	gcWriteBarrier,
 	typedmemmove,
 	typedmemclr,
 	Udiv *obj.LSym

src/cmd/compile/internal/gc/main.go

@@ -44,6 +44,7 @@ var (
 	Debug_slice        int
 	Debug_vlog         bool
 	Debug_wb           int
+	Debug_eagerwb      int
 	Debug_pctab        string
 	Debug_locationlist int
 	Debug_typecheckinl int
@@ -70,6 +71,7 @@ var debugtab = []struct {
 	{"slice", "print information about slice compilation", &Debug_slice},
 	{"typeassert", "print information about type assertion inlining", &Debug_typeassert},
 	{"wb", "print information about write barriers", &Debug_wb},
+	{"eagerwb", "use unbuffered write barrier", &Debug_eagerwb},
 	{"export", "print export data", &Debug_export},
 	{"pctab", "print named pc-value table", &Debug_pctab},
 	{"locationlists", "print information about DWARF location list creation", &Debug_locationlist},
@@ -400,6 +402,12 @@ func Main(archInit func(*Arch)) {
 		Debug['l'] = 1 - Debug['l']
 	}
 
+	// The buffered write barrier is only implemented on amd64
+	// right now.
+	if objabi.GOARCH != "amd64" {
+		Debug_eagerwb = 1
+	}
+
 	trackScopes = flagDWARF && ((Debug['l'] == 0 && Debug['N'] != 0) || Ctxt.Flag_locationlists)
 
 	Widthptr = thearch.LinkArch.PtrSize

src/cmd/compile/internal/gc/ssa.go

@@ -90,6 +90,7 @@ func initssaconfig() {
 	goschedguarded = sysfunc("goschedguarded")
 	writeBarrier = sysfunc("writeBarrier")
 	writebarrierptr = sysfunc("writebarrierptr")
+	gcWriteBarrier = sysfunc("gcWriteBarrier")
 	typedmemmove = sysfunc("typedmemmove")
 	typedmemclr = sysfunc("typedmemclr")
 	Udiv = sysfunc("udiv")
@@ -5185,6 +5186,10 @@ func (e *ssafn) Debug_checknil() bool {
 	return Debug_checknil != 0
 }
 
+func (e *ssafn) Debug_eagerwb() bool {
+	return Debug_eagerwb != 0
+}
+
 func (e *ssafn) UseWriteBarrier() bool {
 	return use_writebarrier
 }
@@ -5197,6 +5202,8 @@ func (e *ssafn) Syslook(name string) *obj.LSym {
 		return writeBarrier
 	case "writebarrierptr":
 		return writebarrierptr
+	case "gcWriteBarrier":
+		return gcWriteBarrier
 	case "typedmemmove":
 		return typedmemmove
 	case "typedmemclr":

src/cmd/compile/internal/ssa/config.go

@@ -88,6 +88,7 @@ type Logger interface {
 
 	// Forwards the Debug flags from gc
 	Debug_checknil() bool
+	Debug_eagerwb() bool
 }
 
 type Frontend interface {

src/cmd/compile/internal/ssa/export_test.go

@@ -134,6 +134,7 @@ func (d DummyFrontend) Log() bool                            { return true }
 func (d DummyFrontend) Fatalf(_ src.XPos, msg string, args ...interface{}) { d.t.Fatalf(msg, args...) }
 func (d DummyFrontend) Warnl(_ src.XPos, msg string, args ...interface{})  { d.t.Logf(msg, args...) }
 func (d DummyFrontend) Debug_checknil() bool                               { return false }
+func (d DummyFrontend) Debug_eagerwb() bool                                { return false }
 
 var dummyTypes Types
 

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -551,6 +551,9 @@
 (AtomicAnd8 ptr val mem) -> (ANDBlock ptr val mem)
 (AtomicOr8 ptr val mem) -> (ORBlock ptr val mem)
 
+// Write barrier.
+(WB {fn} destptr srcptr mem) -> (LoweredWB {fn} destptr srcptr mem)
+
 // ***************************
 // Above: lowering rules
 // Below: optimizations

src/cmd/compile/internal/ssa/gen/AMD64Ops.go

@@ -561,6 +561,10 @@ func init() {
 		//arg0=ptr,arg1=mem, returns void.  Faults if ptr is nil.
 		{name: "LoweredNilCheck", argLength: 2, reg: regInfo{inputs: []regMask{gpsp}}, clobberFlags: true, nilCheck: true, faultOnNilArg0: true},
 
+		// LoweredWB invokes runtime.gcWriteBarrier. arg0=destptr, arg1=srcptr, arg2=mem, aux=runtime.gcWriteBarrier
+		// It saves all GP registers if necessary, but may clobber others.
+		{name: "LoweredWB", argLength: 3, reg: regInfo{inputs: []regMask{buildReg("DI"), ax}, clobbers: callerSave ^ gp}, clobberFlags: true, aux: "Sym", symEffect: "None"},
+
 		// MOVQconvert converts between pointers and integers.
 		// We have a special op for this so as to not confuse GC
 		// (particularly stack maps).  It takes a memory arg so it

src/cmd/compile/internal/ssa/gen/genericOps.go

@@ -331,6 +331,12 @@ var genericOps = []opData{
 	{name: "MoveWB", argLength: 3, typ: "Mem", aux: "TypSize"}, // arg0=destptr, arg1=srcptr, arg2=mem, auxint=size, aux=type.  Returns memory.
 	{name: "ZeroWB", argLength: 2, typ: "Mem", aux: "TypSize"}, // arg0=destptr, arg1=mem, auxint=size, aux=type. Returns memory.
 
+	// WB invokes runtime.gcWriteBarrier. This is not a normal
+	// call: it takes arguments in registers, doesn't clobber
+	// general-purpose registers (the exact clobber set is
+	// arch-dependent), and is not a safe-point.
+	{name: "WB", argLength: 3, typ: "Mem", aux: "Sym", symEffect: "None"}, // arg0=destptr, arg1=srcptr, arg2=mem, aux=runtime.gcWriteBarrier
+
 	// Function calls. Arguments to the call have already been written to the stack.
 	// Return values appear on the stack. The method receiver, if any, is treated
 	// as a phantom first argument.

src/cmd/compile/internal/ssa/opGen.go

@@ -668,6 +668,7 @@ const (
 	OpAMD64LoweredGetCallerPC
 	OpAMD64LoweredGetCallerSP
 	OpAMD64LoweredNilCheck
+	OpAMD64LoweredWB
 	OpAMD64MOVQconvert
 	OpAMD64MOVLconvert
 	OpAMD64FlagEQ
@@ -1923,6 +1924,7 @@ const (
 	OpStoreWB
 	OpMoveWB
 	OpZeroWB
+	OpWB
 	OpClosureCall
 	OpStaticCall
 	OpInterCall
@@ -8155,6 +8157,20 @@ var opcodeTable = [...]opInfo{
 			},
 		},
 	},
+	{
+		name:         "LoweredWB",
+		auxType:      auxSym,
+		argLen:       3,
+		clobberFlags: true,
+		symEffect:    SymNone,
+		reg: regInfo{
+			inputs: []inputInfo{
+				{0, 128}, // DI
+				{1, 1},   // AX
+			},
+			clobbers: 4294901760, // X0 X1 X2 X3 X4 X5 X6 X7 X8 X9 X10 X11 X12 X13 X14 X15
+		},
+	},
 	{
 		name:         "MOVQconvert",
 		argLen:       2,
@@ -23389,6 +23405,13 @@ var opcodeTable = [...]opInfo{
 		argLen:  2,
 		generic: true,
 	},
+	{
+		name:      "WB",
+		auxType:   auxSym,
+		argLen:    3,
+		symEffect: SymNone,
+		generic:   true,
+	},
 	{
 		name:    "ClosureCall",
 		auxType: auxInt64,

src/cmd/compile/internal/ssa/rewriteAMD64.go

@@ -905,6 +905,8 @@ func rewriteValueAMD64(v *Value) bool {
 		return rewriteValueAMD64_OpTrunc64to32_0(v)
 	case OpTrunc64to8:
 		return rewriteValueAMD64_OpTrunc64to8_0(v)
+	case OpWB:
+		return rewriteValueAMD64_OpWB_0(v)
 	case OpXor16:
 		return rewriteValueAMD64_OpXor16_0(v)
 	case OpXor32:
@@ -46955,6 +46957,24 @@ func rewriteValueAMD64_OpTrunc64to8_0(v *Value) bool {
 		return true
 	}
 }
+func rewriteValueAMD64_OpWB_0(v *Value) bool {
+	// match: (WB {fn} destptr srcptr mem)
+	// cond:
+	// result: (LoweredWB {fn} destptr srcptr mem)
+	for {
+		fn := v.Aux
+		_ = v.Args[2]
+		destptr := v.Args[0]
+		srcptr := v.Args[1]
+		mem := v.Args[2]
+		v.reset(OpAMD64LoweredWB)
+		v.Aux = fn
+		v.AddArg(destptr)
+		v.AddArg(srcptr)
+		v.AddArg(mem)
+		return true
+	}
+}
 func rewriteValueAMD64_OpXor16_0(v *Value) bool {
 	// match: (Xor16 x y)
 	// cond:

src/cmd/compile/internal/ssa/writebarrier.go

@@ -44,7 +44,7 @@ func writebarrier(f *Func) {
 	}
 
 	var sb, sp, wbaddr, const0 *Value
-	var writebarrierptr, typedmemmove, typedmemclr *obj.LSym
+	var writebarrierptr, typedmemmove, typedmemclr, gcWriteBarrier *obj.LSym
 	var stores, after []*Value
 	var sset *sparseSet
 	var storeNumber []int32
@@ -97,6 +97,9 @@ func writebarrier(f *Func) {
 			wbsym := f.fe.Syslook("writeBarrier")
 			wbaddr = f.Entry.NewValue1A(initpos, OpAddr, f.Config.Types.UInt32Ptr, wbsym, sb)
 			writebarrierptr = f.fe.Syslook("writebarrierptr")
+			if !f.fe.Debug_eagerwb() {
+				gcWriteBarrier = f.fe.Syslook("gcWriteBarrier")
+			}
 			typedmemmove = f.fe.Syslook("typedmemmove")
 			typedmemclr = f.fe.Syslook("typedmemclr")
 			const0 = f.ConstInt32(initpos, f.Config.Types.UInt32, 0)
@@ -170,6 +173,15 @@ func writebarrier(f *Func) {
 		b.Succs = b.Succs[:0]
 		b.AddEdgeTo(bThen)
 		b.AddEdgeTo(bElse)
+		// TODO: For OpStoreWB and the buffered write barrier,
+		// we could move the write out of the write barrier,
+		// which would lead to fewer branches. We could do
+		// something similar to OpZeroWB, since the runtime
+		// could provide just the barrier half and then we
+		// could unconditionally do an OpZero (which could
+		// also generate better zeroing code). OpMoveWB is
+		// trickier and would require changing how
+		// cgoCheckMemmove works.
 		bThen.AddEdgeTo(bEnd)
 		bElse.AddEdgeTo(bEnd)
 
@@ -205,7 +217,11 @@ func writebarrier(f *Func) {
 			switch w.Op {
 			case OpStoreWB, OpMoveWB, OpZeroWB:
 				volatile := w.Op == OpMoveWB && isVolatile(val)
+				if w.Op == OpStoreWB && !f.fe.Debug_eagerwb() {
+					memThen = bThen.NewValue3A(pos, OpWB, types.TypeMem, gcWriteBarrier, ptr, val, memThen)
+				} else {
 					memThen = wbcall(pos, bThen, fn, typ, ptr, val, memThen, sp, sb, volatile)
+				}
 			case OpVarDef, OpVarLive, OpVarKill:
 				memThen = bThen.NewValue1A(pos, w.Op, types.TypeMem, w.Aux, memThen)
 			}

test/fixedbugs/issue15747.go

@@ -1,4 +1,4 @@
-// errorcheck -0 -live
+// errorcheck -0 -live -d=eagerwb
 
 // Copyright 2016 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -7,6 +7,10 @@
 // Issue 15747: liveness analysis was marking heap-escaped params live too much,
 // and worse was using the wrong bitmap bits to do so.
 
+// TODO(austin): This expects function calls to the write barrier, so
+// we enable the legacy eager write barrier. Fix this once the
+// buffered write barrier works on all arches.
+
 package p
 
 var global *[]byte

test/fixedbugs/issue20250.go

@@ -1,4 +1,4 @@
-// errorcheck -0 -live -d=compilelater
+// errorcheck -0 -live -d=compilelater,eagerwb
 
 // Copyright 2017 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -8,6 +8,10 @@
 // due to propagation of addrtaken to outer variables for
 // closure variables.
 
+// TODO(austin): This expects function calls to the write barrier, so
+// we enable the legacy eager write barrier. Fix this once the
+// buffered write barrier works on all arches.
+
 package p
 
 type T struct {