cmd/compile/internal/gc: steps towards work-queue

This CL reorganizes the top-level functions for handling package-level
declarations, runtime type descriptors, and SSA compilation to work in
a loop. This generalizes the loop that previously existed in dumpdata.

Change-Id: I0e51e60f6ef9e7f96a4a3ccd5801f7baf83eba9a
Reviewed-on: https://go-review.googlesource.com/c/go/+/520611
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

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

@@ -113,10 +113,6 @@ func prepareFunc(fn *ir.Func) {
 // It fans out nBackendWorkers to do the work
 // and waits for them to complete.
 func compileFunctions() {
-	if len(compilequeue) == 0 {
-		return
-	}
-
 	if race.Enabled {
 		// Randomize compilation order to try to shake out races.
 		tmp := make([]*ir.Func, len(compilequeue))

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

@@ -298,18 +298,47 @@ func Main(archInit func(*ssagen.ArchInfo)) {
 
 	ir.CurFunc = nil
 
-	// Compile top level functions.
-	// Don't use range--walk can add functions to Target.Decls.
+	reflectdata.WriteBasicTypes()
+
+	// Compile top-level declarations.
+	//
+	// There are cyclic dependencies between all of these phases, so we
+	// need to iterate all of them until we reach a fixed point.
 	base.Timer.Start("be", "compilefuncs")
-	fcount := int64(0)
-	for i := 0; i < len(typecheck.Target.Funcs); i++ {
-		fn := typecheck.Target.Funcs[i]
-		enqueueFunc(fn)
-		fcount++
+	for nextFunc, nextExtern := 0, 0; ; {
+		reflectdata.WriteRuntimeTypes()
+
+		if nextExtern < len(typecheck.Target.Externs) {
+			switch n := typecheck.Target.Externs[nextExtern]; n.Op() {
+			case ir.ONAME:
+				dumpGlobal(n)
+			case ir.OLITERAL:
+				dumpGlobalConst(n)
+			case ir.OTYPE:
+				reflectdata.NeedRuntimeType(n.Type())
+			}
+			nextExtern++
+			continue
+		}
+
+		if nextFunc < len(typecheck.Target.Funcs) {
+			enqueueFunc(typecheck.Target.Funcs[nextFunc])
+			nextFunc++
+			continue
+		}
+
+		// The SSA backend supports using multiple goroutines, so keep it
+		// as the last step to maximize how much work we can batch and
+		// process concurrently.
+		if len(compilequeue) != 0 {
+			compileFunctions()
+			continue
+		}
+
+		break
 	}
-	base.Timer.AddEvent(fcount, "funcs")
 
-	compileFunctions()
+	base.Timer.AddEvent(int64(len(typecheck.Target.Funcs)), "funcs")
 
 	if base.Flag.CompilingRuntime {
 		// Write barriers are now known. Check the call graph.

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

@@ -110,39 +110,11 @@ func dumpCompilerObj(bout *bio.Writer) {
 }
 
 func dumpdata() {
-	numExterns := len(typecheck.Target.Externs)
-	numDecls := len(typecheck.Target.Funcs)
-	dumpglobls(typecheck.Target.Externs)
-	addsignats(typecheck.Target.Externs)
-	reflectdata.WriteRuntimeTypes()
+	reflectdata.WriteGCSymbols()
 	reflectdata.WritePluginTable()
 	reflectdata.WriteImportStrings()
-	reflectdata.WriteBasicTypes()
 	dumpembeds()
 
-	// Calls to WriteRuntimeTypes can generate functions,
-	// like method wrappers and hash and equality routines.
-	// Compile any generated functions, process any new resulting types, repeat.
-	// This can't loop forever, because there is no way to generate an infinite
-	// number of types in a finite amount of code.
-	// In the typical case, we loop 0 or 1 times.
-	// It was not until issue 24761 that we found any code that required a loop at all.
-	for {
-		for i := numDecls; i < len(typecheck.Target.Funcs); i++ {
-			fn := typecheck.Target.Funcs[i]
-			enqueueFunc(fn)
-		}
-		numDecls = len(typecheck.Target.Funcs)
-		compileFunctions()
-		reflectdata.WriteRuntimeTypes()
-		if numDecls == len(typecheck.Target.Funcs) {
-			break
-		}
-	}
-
-	// Dump extra globals.
-	dumpglobls(typecheck.Target.Externs[numExterns:])
-
 	if reflectdata.ZeroSize > 0 {
 		zero := base.PkgLinksym("go:map", "zero", obj.ABI0)
 		objw.Global(zero, int32(reflectdata.ZeroSize), obj.DUPOK|obj.RODATA)
@@ -217,18 +189,6 @@ func dumpGlobalConst(n *ir.Name) {
 	base.Ctxt.DwarfIntConst(base.Ctxt.Pkgpath, n.Sym().Name, types.TypeSymName(t), ir.IntVal(t, v))
 }
 
-func dumpglobls(externs []*ir.Name) {
-	// add globals
-	for _, n := range externs {
-		switch n.Op() {
-		case ir.ONAME:
-			dumpGlobal(n)
-		case ir.OLITERAL:
-			dumpGlobalConst(n)
-		}
-	}
-}
-
 // addGCLocals adds gcargs, gclocals, gcregs, and stack object symbols to Ctxt.Data.
 //
 // This is done during the sequential phase after compilation, since
@@ -323,12 +283,3 @@ func dumpembeds() {
 		staticdata.WriteEmbed(v)
 	}
 }
-
-func addsignats(dcls []*ir.Name) {
-	// copy types from dcl list to signatset
-	for _, n := range dcls {
-		if n.Op() == ir.OTYPE {
-			reflectdata.NeedRuntimeType(n.Type())
-		}
-	}
-}

src/cmd/compile/internal/reflectdata/reflect.go

@@ -1264,7 +1264,9 @@ func WriteRuntimeTypes() {
 		}
 		signatslice = signatslice[len(signats):]
 	}
+}
 
+func WriteGCSymbols() {
 	// Emit GC data symbols.
 	gcsyms := make([]typeAndStr, 0, len(gcsymset))
 	for t := range gcsymset {