runtime: remove legacy eager write barrier

Now that the buffered write barrier is implemented for all
architectures, we can remove the old eager write barrier
implementation. This CL removes the implementation from the runtime,
support in the compiler for calling it, and updates some compiler
tests that relied on the old eager barrier support. It also makes sure
that all of the useful comments from the old write barrier
implementation still have a place to live.

Fixes #22460.

Updates #21640 since this fixes the layering concerns of the write
barrier (but not the other things in that issue).

Change-Id: I580f93c152e89607e0a72fe43370237ba97bae74
Reviewed-on: https://go-review.googlesource.com/92705
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Rick Hudson <rlh@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

9 files changed, 78 insertions, 109 deletions

diff --git a/src/cmd/compile/internal/gc/asm_test.go b/src/cmd/compile/internal/gc/asm_test.go
index 50857e6533..73c55018f9 100644
--- a/src/cmd/compile/internal/gc/asm_test.go
+++ b/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|gcWriteBarrier)\\(SB\\)"},
+		pos: []string{"\tXORPS\tX., X", "\tMOVUPS\tX., \\(.*\\)", "\tMOVQ\t\\$0, 16\\(.*\\)", "\tCALL\truntime\\.gcWriteBarrier\\(SB\\)"},
 	},
 	// Rotate tests
 	{
diff --git a/src/cmd/compile/internal/gc/builtin.go b/src/cmd/compile/internal/gc/builtin.go
index 0733a460d5..3bb17673a5 100644
--- a/src/cmd/compile/internal/gc/builtin.go
+++ b/src/cmd/compile/internal/gc/builtin.go
@@ -105,56 +105,55 @@ var runtimeDecls = [...]struct {
 	{"chansend1", funcTag, 81},
 	{"closechan", funcTag, 23},
 	{"writeBarrier", varTag, 83},
-	{"writebarrierptr", funcTag, 84},
-	{"typedmemmove", funcTag, 85},
-	{"typedmemclr", funcTag, 86},
-	{"typedslicecopy", funcTag, 87},
-	{"selectnbsend", funcTag, 88},
-	{"selectnbrecv", funcTag, 89},
-	{"selectnbrecv2", funcTag, 91},
-	{"newselect", funcTag, 92},
-	{"selectsend", funcTag, 93},
-	{"selectrecv", funcTag, 94},
+	{"typedmemmove", funcTag, 84},
+	{"typedmemclr", funcTag, 85},
+	{"typedslicecopy", funcTag, 86},
+	{"selectnbsend", funcTag, 87},
+	{"selectnbrecv", funcTag, 88},
+	{"selectnbrecv2", funcTag, 90},
+	{"newselect", funcTag, 91},
+	{"selectsend", funcTag, 92},
+	{"selectrecv", funcTag, 93},
 	{"selectdefault", funcTag, 55},
-	{"selectgo", funcTag, 95},
+	{"selectgo", funcTag, 94},
 	{"block", funcTag, 5},
-	{"makeslice", funcTag, 97},
-	{"makeslice64", funcTag, 98},
-	{"growslice", funcTag, 99},
-	{"memmove", funcTag, 100},
-	{"memclrNoHeapPointers", funcTag, 101},
-	{"memclrHasPointers", funcTag, 101},
-	{"memequal", funcTag, 102},
-	{"memequal8", funcTag, 103},
-	{"memequal16", funcTag, 103},
-	{"memequal32", funcTag, 103},
-	{"memequal64", funcTag, 103},
-	{"memequal128", funcTag, 103},
-	{"int64div", funcTag, 104},
-	{"uint64div", funcTag, 105},
-	{"int64mod", funcTag, 104},
-	{"uint64mod", funcTag, 105},
-	{"float64toint64", funcTag, 106},
-	{"float64touint64", funcTag, 107},
-	{"float64touint32", funcTag, 108},
-	{"int64tofloat64", funcTag, 109},
-	{"uint64tofloat64", funcTag, 110},
-	{"uint32tofloat64", funcTag, 111},
-	{"complex128div", funcTag, 112},
-	{"racefuncenter", funcTag, 113},
+	{"makeslice", funcTag, 96},
+	{"makeslice64", funcTag, 97},
+	{"growslice", funcTag, 98},
+	{"memmove", funcTag, 99},
+	{"memclrNoHeapPointers", funcTag, 100},
+	{"memclrHasPointers", funcTag, 100},
+	{"memequal", funcTag, 101},
+	{"memequal8", funcTag, 102},
+	{"memequal16", funcTag, 102},
+	{"memequal32", funcTag, 102},
+	{"memequal64", funcTag, 102},
+	{"memequal128", funcTag, 102},
+	{"int64div", funcTag, 103},
+	{"uint64div", funcTag, 104},
+	{"int64mod", funcTag, 103},
+	{"uint64mod", funcTag, 104},
+	{"float64toint64", funcTag, 105},
+	{"float64touint64", funcTag, 106},
+	{"float64touint32", funcTag, 107},
+	{"int64tofloat64", funcTag, 108},
+	{"uint64tofloat64", funcTag, 109},
+	{"uint32tofloat64", funcTag, 110},
+	{"complex128div", funcTag, 111},
+	{"racefuncenter", funcTag, 112},
 	{"racefuncexit", funcTag, 5},
-	{"raceread", funcTag, 113},
-	{"racewrite", funcTag, 113},
-	{"racereadrange", funcTag, 114},
-	{"racewriterange", funcTag, 114},
-	{"msanread", funcTag, 114},
-	{"msanwrite", funcTag, 114},
+	{"raceread", funcTag, 112},
+	{"racewrite", funcTag, 112},
+	{"racereadrange", funcTag, 113},
+	{"racewriterange", funcTag, 113},
+	{"msanread", funcTag, 113},
+	{"msanwrite", funcTag, 113},
 	{"support_popcnt", varTag, 11},
 	{"support_sse41", varTag, 11},
 }
 
 func runtimeTypes() []*types.Type {
-	var typs [115]*types.Type
+	var typs [114]*types.Type
 	typs[0] = types.Bytetype
 	typs[1] = types.NewPtr(typs[0])
 	typs[2] = types.Types[TANY]
@@ -239,36 +238,35 @@ func runtimeTypes() []*types.Type {
 	typs[81] = functype(nil, []*Node{anonfield(typs[80]), anonfield(typs[3])}, nil)
 	typs[82] = types.NewArray(typs[0], 3)
 	typs[83] = tostruct([]*Node{namedfield("enabled", typs[11]), namedfield("pad", typs[82]), namedfield("needed", typs[11]), namedfield("cgo", typs[11]), namedfield("alignme", typs[17])})
-	typs[84] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[2])}, nil)
-	typs[85] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[3]), anonfield(typs[3])}, nil)
-	typs[86] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[3])}, nil)
-	typs[87] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[2]), anonfield(typs[2])}, []*Node{anonfield(typs[32])})
-	typs[88] = functype(nil, []*Node{anonfield(typs[80]), anonfield(typs[3])}, []*Node{anonfield(typs[11])})
-	typs[89] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[77])}, []*Node{anonfield(typs[11])})
-	typs[90] = types.NewPtr(typs[11])
-	typs[91] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[90]), anonfield(typs[77])}, []*Node{anonfield(typs[11])})
-	typs[92] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[15]), anonfield(typs[8])}, nil)
-	typs[93] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[80]), anonfield(typs[3])}, nil)
-	typs[94] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[77]), anonfield(typs[3]), anonfield(typs[90])}, nil)
-	typs[95] = functype(nil, []*Node{anonfield(typs[1])}, []*Node{anonfield(typs[32])})
-	typs[96] = types.NewSlice(typs[2])
-	typs[97] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[32]), anonfield(typs[32])}, []*Node{anonfield(typs[96])})
-	typs[98] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[15]), anonfield(typs[15])}, []*Node{anonfield(typs[96])})
-	typs[99] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[96]), anonfield(typs[32])}, []*Node{anonfield(typs[96])})
-	typs[100] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[3]), anonfield(typs[48])}, nil)
-	typs[101] = functype(nil, []*Node{anonfield(typs[57]), anonfield(typs[48])}, nil)
-	typs[102] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[3]), anonfield(typs[48])}, []*Node{anonfield(typs[11])})
-	typs[103] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[3])}, []*Node{anonfield(typs[11])})
-	typs[104] = functype(nil, []*Node{anonfield(typs[15]), anonfield(typs[15])}, []*Node{anonfield(typs[15])})
-	typs[105] = functype(nil, []*Node{anonfield(typs[17]), anonfield(typs[17])}, []*Node{anonfield(typs[17])})
-	typs[106] = functype(nil, []*Node{anonfield(typs[13])}, []*Node{anonfield(typs[15])})
-	typs[107] = functype(nil, []*Node{anonfield(typs[13])}, []*Node{anonfield(typs[17])})
-	typs[108] = functype(nil, []*Node{anonfield(typs[13])}, []*Node{anonfield(typs[59])})
-	typs[109] = functype(nil, []*Node{anonfield(typs[15])}, []*Node{anonfield(typs[13])})
-	typs[110] = functype(nil, []*Node{anonfield(typs[17])}, []*Node{anonfield(typs[13])})
-	typs[111] = functype(nil, []*Node{anonfield(typs[59])}, []*Node{anonfield(typs[13])})
-	typs[112] = functype(nil, []*Node{anonfield(typs[19]), anonfield(typs[19])}, []*Node{anonfield(typs[19])})
-	typs[113] = functype(nil, []*Node{anonfield(typs[48])}, nil)
-	typs[114] = functype(nil, []*Node{anonfield(typs[48]), anonfield(typs[48])}, nil)
+	typs[84] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[3]), anonfield(typs[3])}, nil)
+	typs[85] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[3])}, nil)
+	typs[86] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[2]), anonfield(typs[2])}, []*Node{anonfield(typs[32])})
+	typs[87] = functype(nil, []*Node{anonfield(typs[80]), anonfield(typs[3])}, []*Node{anonfield(typs[11])})
+	typs[88] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[77])}, []*Node{anonfield(typs[11])})
+	typs[89] = types.NewPtr(typs[11])
+	typs[90] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[89]), anonfield(typs[77])}, []*Node{anonfield(typs[11])})
+	typs[91] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[15]), anonfield(typs[8])}, nil)
+	typs[92] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[80]), anonfield(typs[3])}, nil)
+	typs[93] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[77]), anonfield(typs[3]), anonfield(typs[89])}, nil)
+	typs[94] = functype(nil, []*Node{anonfield(typs[1])}, []*Node{anonfield(typs[32])})
+	typs[95] = types.NewSlice(typs[2])
+	typs[96] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[32]), anonfield(typs[32])}, []*Node{anonfield(typs[95])})
+	typs[97] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[15]), anonfield(typs[15])}, []*Node{anonfield(typs[95])})
+	typs[98] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[95]), anonfield(typs[32])}, []*Node{anonfield(typs[95])})
+	typs[99] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[3]), anonfield(typs[48])}, nil)
+	typs[100] = functype(nil, []*Node{anonfield(typs[57]), anonfield(typs[48])}, nil)
+	typs[101] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[3]), anonfield(typs[48])}, []*Node{anonfield(typs[11])})
+	typs[102] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[3])}, []*Node{anonfield(typs[11])})
+	typs[103] = functype(nil, []*Node{anonfield(typs[15]), anonfield(typs[15])}, []*Node{anonfield(typs[15])})
+	typs[104] = functype(nil, []*Node{anonfield(typs[17]), anonfield(typs[17])}, []*Node{anonfield(typs[17])})
+	typs[105] = functype(nil, []*Node{anonfield(typs[13])}, []*Node{anonfield(typs[15])})
+	typs[106] = functype(nil, []*Node{anonfield(typs[13])}, []*Node{anonfield(typs[17])})
+	typs[107] = functype(nil, []*Node{anonfield(typs[13])}, []*Node{anonfield(typs[59])})
+	typs[108] = functype(nil, []*Node{anonfield(typs[15])}, []*Node{anonfield(typs[13])})
+	typs[109] = functype(nil, []*Node{anonfield(typs[17])}, []*Node{anonfield(typs[13])})
+	typs[110] = functype(nil, []*Node{anonfield(typs[59])}, []*Node{anonfield(typs[13])})
+	typs[111] = functype(nil, []*Node{anonfield(typs[19]), anonfield(typs[19])}, []*Node{anonfield(typs[19])})
+	typs[112] = functype(nil, []*Node{anonfield(typs[48])}, nil)
+	typs[113] = functype(nil, []*Node{anonfield(typs[48]), anonfield(typs[48])}, nil)
 	return typs[:]
 }
diff --git a/src/cmd/compile/internal/gc/builtin/runtime.go b/src/cmd/compile/internal/gc/builtin/runtime.go
index de17d51d8a..bda9d1d03c 100644
--- a/src/cmd/compile/internal/gc/builtin/runtime.go
+++ b/src/cmd/compile/internal/gc/builtin/runtime.go
@@ -136,8 +136,6 @@ var writeBarrier struct {
 	alignme uint64
 }
 
-func writebarrierptr(dst *any, src any)
-
 // *byte is really *runtime.Type
 func typedmemmove(typ *byte, dst *any, src *any)
 func typedmemclr(typ *byte, dst *any)
diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index dc94cf4f98..d6db7acc59 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -292,7 +292,6 @@ var (
 	assertI2I2,
 	goschedguarded,
 	writeBarrier,
-	writebarrierptr,
 	gcWriteBarrier,
 	typedmemmove,
 	typedmemclr,
diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
index 7f947530b1..f1591c16d2 100644
--- a/src/cmd/compile/internal/gc/main.go
+++ b/src/cmd/compile/internal/gc/main.go
@@ -44,7 +44,6 @@ var (
 	Debug_slice        int
 	Debug_vlog         bool
 	Debug_wb           int
-	Debug_eagerwb      int
 	Debug_pctab        string
 	Debug_locationlist int
 	Debug_typecheckinl int
@@ -73,7 +72,6 @@ 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},
@@ -407,14 +405,6 @@ func Main(archInit func(*Arch)) {
 		Debug['l'] = 1 - Debug['l']
 	}
 
-	switch objabi.GOARCH {
-	case "amd64", "amd64p32", "386", "arm", "arm64", "ppc64", "ppc64le", "mips64", "mips64le", "mips", "mipsle", "s390x":
-	default:
-		// Other architectures don't support the buffered
-		// write barrier yet.
-		Debug_eagerwb = 1
-	}
-
 	trackScopes = flagDWARF && ((Debug['l'] == 0 && Debug['N'] != 0) || Ctxt.Flag_locationlists)
 
 	Widthptr = thearch.LinkArch.PtrSize
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index fe062da409..5ec01b6a61 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -95,7 +95,6 @@ func initssaconfig() {
 	assertI2I2 = sysfunc("assertI2I2")
 	goschedguarded = sysfunc("goschedguarded")
 	writeBarrier = sysfunc("writeBarrier")
-	writebarrierptr = sysfunc("writebarrierptr")
 	gcWriteBarrier = sysfunc("gcWriteBarrier")
 	typedmemmove = sysfunc("typedmemmove")
 	typedmemclr = sysfunc("typedmemclr")
@@ -5380,10 +5379,6 @@ 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
 }
@@ -5394,8 +5389,6 @@ func (e *ssafn) Syslook(name string) *obj.LSym {
 		return goschedguarded
 	case "writeBarrier":
 		return writeBarrier
-	case "writebarrierptr":
-		return writebarrierptr
 	case "gcWriteBarrier":
 		return gcWriteBarrier
 	case "typedmemmove":
diff --git a/src/cmd/compile/internal/ssa/config.go b/src/cmd/compile/internal/ssa/config.go
index 725cdcd9a4..13e5c50da1 100644
--- a/src/cmd/compile/internal/ssa/config.go
+++ b/src/cmd/compile/internal/ssa/config.go
@@ -89,7 +89,6 @@ type Logger interface {
 
 	// Forwards the Debug flags from gc
 	Debug_checknil() bool
-	Debug_eagerwb() bool
 }
 
 type Frontend interface {
diff --git a/src/cmd/compile/internal/ssa/export_test.go b/src/cmd/compile/internal/ssa/export_test.go
index 28ae494505..d1d6831eb3 100644
--- a/src/cmd/compile/internal/ssa/export_test.go
+++ b/src/cmd/compile/internal/ssa/export_test.go
@@ -134,7 +134,6 @@ 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
 
diff --git a/src/cmd/compile/internal/ssa/writebarrier.go b/src/cmd/compile/internal/ssa/writebarrier.go
index b711d8d2bf..c41a677159 100644
--- a/src/cmd/compile/internal/ssa/writebarrier.go
+++ b/src/cmd/compile/internal/ssa/writebarrier.go
@@ -31,7 +31,7 @@ func needwb(v *Value) bool {
 // and runtime calls, like
 //
 // if writeBarrier.enabled {
-//   writebarrierptr(ptr, val)
+//   gcWriteBarrier(ptr, val)	// Not a regular Go call
 // } else {
 //   *ptr = val
 // }
@@ -44,7 +44,7 @@ func writebarrier(f *Func) {
 	}
 
 	var sb, sp, wbaddr, const0 *Value
-	var writebarrierptr, typedmemmove, typedmemclr, gcWriteBarrier *obj.LSym
+	var typedmemmove, typedmemclr, gcWriteBarrier *obj.LSym
 	var stores, after []*Value
 	var sset *sparseSet
 	var storeNumber []int32
@@ -96,10 +96,7 @@ 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")
-			}
+			gcWriteBarrier = f.fe.Syslook("gcWriteBarrier")
 			typedmemmove = f.fe.Syslook("typedmemmove")
 			typedmemclr = f.fe.Syslook("typedmemclr")
 			const0 = f.ConstInt32(initpos, f.Config.Types.UInt32, 0)
@@ -198,7 +195,6 @@ func writebarrier(f *Func) {
 			var val *Value
 			switch w.Op {
 			case OpStoreWB:
-				fn = writebarrierptr
 				val = w.Args[1]
 				nWBops--
 			case OpMoveWB:
@@ -217,11 +213,13 @@ 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() {
+				if w.Op == OpStoreWB {
 					memThen = bThen.NewValue3A(pos, OpWB, types.TypeMem, gcWriteBarrier, ptr, val, memThen)
 				} else {
 					memThen = wbcall(pos, bThen, fn, typ, ptr, val, memThen, sp, sb, volatile)
 				}
+				// Note that we set up a writebarrier function call.
+				f.fe.SetWBPos(pos)
 			case OpVarDef, OpVarLive, OpVarKill:
 				memThen = bThen.NewValue1A(pos, w.Op, types.TypeMem, w.Aux, memThen)
 			}
@@ -239,11 +237,6 @@ func writebarrier(f *Func) {
 			case OpVarDef, OpVarLive, OpVarKill:
 				memElse = bElse.NewValue1A(pos, w.Op, types.TypeMem, w.Aux, memElse)
 			}
-
-			if fn != nil {
-				// Note that we set up a writebarrier function call.
-				f.fe.SetWBPos(pos)
-			}
 		}
 
 		// merge memory