[dev.typeparams] cmd/compile: refactor closure construction

typecheck.tcClosure is complicated with many code flows because all of
its callers setup the closure funcs in slightly different ways. E.g.,
it's non-obvious who's responsible for setting the underlying func's
Sym or adding it to target.Decls, or how to write new code that
constructs a closure without interfering with existing code.

This CL refactors everything to use three common functions in package
ir: NewClosureFunc (which handle creating the Func, Name, and
ClosureExpr and wiring them together), NameClosure (which generates
and assigns its unique Sym), and UseClosure (which handles adding the
Func to target.Decls).

Most IR builders can actually name the closure right away, but the
legacy noder+typecheck path may not yet know the name of the enclosing
function. In particular, for methods declared with aliased receiver
parameters, we need to wait until after typechecking top-level
declarations to know the method's true name. So they're left anonymous
until typecheck.

UseClosure does relatively little work today, but it serves as a
useful spot to check that the code setting up closures got it right.
It may also eventually serve as an optimization point for early
lifting of trivial closures, which may or may not ultimately be
beneficial.

Change-Id: I7da1e93c70d268f575b12d6aaeb2336eb910a6f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/327051
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

2 files changed, 101 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ir/expr.go b/src/cmd/compile/internal/ir/expr.go
index bcc0e412d5..779793b2f2 100644
--- a/src/cmd/compile/internal/ir/expr.go
+++ b/src/cmd/compile/internal/ir/expr.go
@@ -195,6 +195,7 @@ type ClosureExpr struct {
 	IsGoWrap bool // whether this is wrapper closure of a go statement
 }
 
+// Deprecated: Use NewClosureFunc instead.
 func NewClosureExpr(pos src.XPos, fn *Func) *ClosureExpr {
 	n := &ClosureExpr{Func: fn}
 	n.op = OCLOSURE
diff --git a/src/cmd/compile/internal/ir/func.go b/src/cmd/compile/internal/ir/func.go
index 1d76813a4c..3d4f8c4486 100644
--- a/src/cmd/compile/internal/ir/func.go
+++ b/src/cmd/compile/internal/ir/func.go
@@ -9,6 +9,7 @@ import (
 	"cmd/compile/internal/types"
 	"cmd/internal/obj"
 	"cmd/internal/src"
+	"fmt"
 )
 
 // A Func corresponds to a single function in a Go program
@@ -311,3 +312,102 @@ func ClosureDebugRuntimeCheck(clo *ClosureExpr) {
 func IsTrivialClosure(clo *ClosureExpr) bool {
 	return len(clo.Func.ClosureVars) == 0
 }
+
+// globClosgen is like Func.Closgen, but for the global scope.
+var globClosgen int32
+
+// closureName generates a new unique name for a closure within outerfn.
+func closureName(outerfn *Func) *types.Sym {
+	pkg := types.LocalPkg
+	outer := "glob."
+	prefix := "func"
+	gen := &globClosgen
+
+	if outerfn != nil {
+		if outerfn.OClosure != nil {
+			prefix = ""
+		}
+
+		pkg = outerfn.Sym().Pkg
+		outer = FuncName(outerfn)
+
+		// There may be multiple functions named "_". In those
+		// cases, we can't use their individual Closgens as it
+		// would lead to name clashes.
+		if !IsBlank(outerfn.Nname) {
+			gen = &outerfn.Closgen
+		}
+	}
+
+	*gen++
+	return pkg.Lookup(fmt.Sprintf("%s.%s%d", outer, prefix, *gen))
+}
+
+// NewClosureFunc creates a new Func to represent a function literal
+// within outerfn.
+func NewClosureFunc(pos src.XPos, outerfn *Func) *Func {
+	fn := NewFunc(pos)
+	fn.SetIsHiddenClosure(outerfn != nil)
+
+	fn.Nname = NewNameAt(pos, BlankNode.Sym())
+	fn.Nname.Func = fn
+	fn.Nname.Defn = fn
+
+	fn.OClosure = NewClosureExpr(pos, fn)
+
+	return fn
+}
+
+// NameClosure generates a unique for the given function literal,
+// which must have appeared within outerfn.
+func NameClosure(clo *ClosureExpr, outerfn *Func) {
+	name := clo.Func.Nname
+	if !IsBlank(name) {
+		base.FatalfAt(clo.Pos(), "closure already named: %v", name)
+	}
+
+	name.SetSym(closureName(outerfn))
+	MarkFunc(name)
+}
+
+// UseClosure checks that the ginen function literal has been setup
+// correctly, and then returns it as an expression.
+// It must be called after clo.Func.ClosureVars has been set.
+func UseClosure(clo *ClosureExpr, pkg *Package) Node {
+	fn := clo.Func
+	name := fn.Nname
+
+	if IsBlank(name) {
+		base.FatalfAt(fn.Pos(), "unnamed closure func: %v", fn)
+	}
+	// Caution: clo.Typecheck() is still 0 when UseClosure is called by
+	// tcClosure.
+	if fn.Typecheck() != 1 || name.Typecheck() != 1 {
+		base.FatalfAt(fn.Pos(), "missed typecheck: %v", fn)
+	}
+	if clo.Type() == nil || name.Type() == nil {
+		base.FatalfAt(fn.Pos(), "missing types: %v", fn)
+	}
+	if !types.Identical(clo.Type(), name.Type()) {
+		base.FatalfAt(fn.Pos(), "mismatched types: %v", fn)
+	}
+
+	if base.Flag.W > 1 {
+		s := fmt.Sprintf("new closure func: %v", fn)
+		Dump(s, fn)
+	}
+
+	if pkg != nil {
+		pkg.Decls = append(pkg.Decls, fn)
+	}
+
+	if false && IsTrivialClosure(clo) {
+		// TODO(mdempsky): Investigate if we can/should optimize this
+		// case. walkClosure already handles it later, but it could be
+		// useful to recognize earlier (e.g., it might allow multiple
+		// inlined calls to a function to share a common trivial closure
+		// func, rather than cloning it for each inlined call).
+	}
+
+	return clo
+}