[dev.regabi] cmd/compile: compile functions before closures

This CL reorders function compilation to ensure that functions are
always compiled before any enclosed function literals. The primary
goal of this is to reduce the risk of race conditions that arise due
to compilation of function literals needing to inspect data from their
closure variables. However, a pleasant side effect is that it allows
skipping the redundant, separate compilation of function literals that
were inlined into their enclosing function.

Change-Id: I03ee96212988cb578c2452162b7e99cc5e92918f
Reviewed-on: https://go-review.googlesource.com/c/go/+/282892
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>

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

@@ -37,6 +37,10 @@ func enqueueFunc(fn *ir.Func) {
 		return
 	}
 
+	if clo := fn.OClosure; clo != nil && !ir.IsTrivialClosure(clo) {
+		return // we'll get this as part of its enclosing function
+	}
+
 	if len(fn.Body) == 0 {
 		// Initialize ABI wrappers if necessary.
 		ssagen.InitLSym(fn, false)
@@ -45,11 +49,22 @@ func enqueueFunc(fn *ir.Func) {
 	}
 
 	errorsBefore := base.Errors()
-	prepareFunc(fn)
+
+	todo := []*ir.Func{fn}
+	for len(todo) > 0 {
+		next := todo[len(todo)-1]
+		todo = todo[:len(todo)-1]
+
+		prepareFunc(next)
+		todo = append(todo, next.Closures...)
+	}
+
 	if base.Errors() > errorsBefore {
 		return
 	}
 
+	// Enqueue just fn itself. compileFunctions will handle
+	// scheduling compilation of its closures after it's done.
 	compilequeue = append(compilequeue, fn)
 }
 
@@ -97,7 +112,6 @@ func compileFunctions() {
 		return
 	}
 
-	types.CalcSizeDisabled = true // not safe to calculate sizes concurrently
 	if race.Enabled {
 		// Randomize compilation order to try to shake out races.
 		tmp := make([]*ir.Func, len(compilequeue))
@@ -114,22 +128,37 @@ func compileFunctions() {
 			return len(compilequeue[i].Body) > len(compilequeue[j].Body)
 		})
 	}
-	var wg sync.WaitGroup
-	base.Ctxt.InParallel = true
-	c := make(chan *ir.Func, base.Flag.LowerC)
+
+	// We queue up a goroutine per function that needs to be
+	// compiled, but require them to grab an available worker ID
+	// before doing any substantial work to limit parallelism.
+	workerIDs := make(chan int, base.Flag.LowerC)
 	for i := 0; i < base.Flag.LowerC; i++ {
+		workerIDs <- i
+	}
+
+	var wg sync.WaitGroup
+	var asyncCompile func(*ir.Func)
+	asyncCompile = func(fn *ir.Func) {
 		wg.Add(1)
-		go func(worker int) {
-			for fn := range c {
-				ssagen.Compile(fn, worker)
+		go func() {
+			worker := <-workerIDs
+			ssagen.Compile(fn, worker)
+			workerIDs <- worker
+
+			// Done compiling fn. Schedule it's closures for compilation.
+			for _, closure := range fn.Closures {
+				asyncCompile(closure)
 			}
 			wg.Done()
-		}(i)
+		}()
 	}
+
+	types.CalcSizeDisabled = true // not safe to calculate sizes concurrently
+	base.Ctxt.InParallel = true
 	for _, fn := range compilequeue {
-		c <- fn
+		asyncCompile(fn)
 	}
-	close(c)
 	compilequeue = nil
 	wg.Wait()
 	base.Ctxt.InParallel = false

src/cmd/compile/internal/ir/func.go

@@ -81,6 +81,10 @@ type Func struct {
 	// Byval set if they're captured by value.
 	ClosureVars []*Name
 
+	// Enclosed functions that need to be compiled.
+	// Populated during walk.
+	Closures []*Func
+
 	// Parents records the parent scope of each scope within a
 	// function. The root scope (0) has no parent, so the i'th
 	// scope's parent is stored at Parents[i-1].

src/cmd/compile/internal/ir/sizeof_test.go

@@ -20,7 +20,7 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Func{}, 184, 320},
+		{Func{}, 196, 344},
 		{Name{}, 116, 208},
 	}
 

src/cmd/compile/internal/walk/closure.go

@@ -86,6 +86,8 @@ func walkClosure(clo *ir.ClosureExpr, init *ir.Nodes) ir.Node {
 		}
 		return fn.Nname
 	}
+
+	ir.CurFunc.Closures = append(ir.CurFunc.Closures, fn)
 	ir.ClosureDebugRuntimeCheck(clo)
 
 	typ := typecheck.ClosureType(clo)

src/cmd/compile/internal/walk/expr.go

@@ -488,12 +488,15 @@ func walkCall(n *ir.CallExpr, init *ir.Nodes) ir.Node {
 		reflectdata.MarkUsedIfaceMethod(n)
 	}
 
-	if n.Op() == ir.OCALLFUNC && n.X.Op() == ir.OCLOSURE {
+	if n.Op() == ir.OCALLFUNC && n.X.Op() == ir.OCLOSURE && !ir.IsTrivialClosure(n.X.(*ir.ClosureExpr)) {
 		// Transform direct call of a closure to call of a normal function.
 		// transformclosure already did all preparation work.
+		// We leave trivial closures for walkClosure to handle.
+
+		clo := n.X.(*ir.ClosureExpr)
+		ir.CurFunc.Closures = append(ir.CurFunc.Closures, clo.Func)
 
 		// Prepend captured variables to argument list.
-		clo := n.X.(*ir.ClosureExpr)
 		n.Args.Prepend(closureArgs(clo)...)
 
 		// Replace OCLOSURE with ONAME/PFUNC.