1 files changed, 85 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/devirtualize/devirtualize.go b/src/cmd/compile/internal/devirtualize/devirtualize.go
new file mode 100644
index 0000000..60ba208
--- /dev/null
+++ b/src/cmd/compile/internal/devirtualize/devirtualize.go
@@ -0,0 +1,85 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package devirtualize implements a simple "devirtualization"
+// optimization pass, which replaces interface method calls with
+// direct concrete-type method calls where possible.
+package devirtualize
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+)
+
+// Func devirtualizes calls within fn where possible.
+func Func(fn *ir.Func) {
+	ir.CurFunc = fn
+	ir.VisitList(fn.Body, func(n ir.Node) {
+		if call, ok := n.(*ir.CallExpr); ok {
+			Call(call)
+		}
+	})
+}
+
+// Call devirtualizes the given call if possible.
+func Call(call *ir.CallExpr) {
+	if call.Op() != ir.OCALLINTER {
+		return
+	}
+	sel := call.X.(*ir.SelectorExpr)
+	r := ir.StaticValue(sel.X)
+	if r.Op() != ir.OCONVIFACE {
+		return
+	}
+	recv := r.(*ir.ConvExpr)
+
+	typ := recv.X.Type()
+	if typ.IsInterface() {
+		return
+	}
+
+	dt := ir.NewTypeAssertExpr(sel.Pos(), sel.X, nil)
+	dt.SetType(typ)
+	x := typecheck.Callee(ir.NewSelectorExpr(sel.Pos(), ir.OXDOT, dt, sel.Sel))
+	switch x.Op() {
+	case ir.ODOTMETH:
+		x := x.(*ir.SelectorExpr)
+		if base.Flag.LowerM != 0 {
+			base.WarnfAt(call.Pos(), "devirtualizing %v to %v", sel, typ)
+		}
+		call.SetOp(ir.OCALLMETH)
+		call.X = x
+	case ir.ODOTINTER:
+		// Promoted method from embedded interface-typed field (#42279).
+		x := x.(*ir.SelectorExpr)
+		if base.Flag.LowerM != 0 {
+			base.WarnfAt(call.Pos(), "partially devirtualizing %v to %v", sel, typ)
+		}
+		call.SetOp(ir.OCALLINTER)
+		call.X = x
+	default:
+		// TODO(mdempsky): Turn back into Fatalf after more testing.
+		if base.Flag.LowerM != 0 {
+			base.WarnfAt(call.Pos(), "failed to devirtualize %v (%v)", x, x.Op())
+		}
+		return
+	}
+
+	// Duplicated logic from typecheck for function call return
+	// value types.
+	//
+	// Receiver parameter size may have changed; need to update
+	// call.Type to get correct stack offsets for result
+	// parameters.
+	types.CheckSize(x.Type())
+	switch ft := x.Type(); ft.NumResults() {
+	case 0:
+	case 1:
+		call.SetType(ft.Results().Field(0).Type)
+	default:
+		call.SetType(ft.Results())
+	}
+}