cmd/compile/internal/devirtualize: devirtualize methods in other packages if current package has a concrete reference

src/cmd/compile/internal/devirtualize/pgo.go

@@ -357,11 +357,11 @@ func rewriteCondCall(call *ir.CallExpr, curfn, callee *ir.Func, concretetyp *typ
 		elseBlock.Append(call)
 	} else {
 		// Copy slice so edits in one location don't affect another.
-		thenRet := append([]ir.Node(nil),  retvars...)
+		thenRet := append([]ir.Node(nil), retvars...)
 		thenAsList := ir.NewAssignListStmt(pos, ir.OAS2, thenRet, []ir.Node{concreteCall})
 		thenBlock.Append(typecheck.Stmt(thenAsList))
 
-		elseRet := append([]ir.Node(nil),  retvars...)
+		elseRet := append([]ir.Node(nil), retvars...)
 		elseAsList := ir.NewAssignListStmt(pos, ir.OAS2, elseRet, []ir.Node{call})
 		elseBlock.Append(typecheck.Stmt(elseAsList))
 	}

src/cmd/compile/internal/inline/inl.go

@@ -414,8 +414,9 @@ func InlineImpossible(fn *ir.Func) string {
 		return reason
 	}
 
-	// If fn has no body (is defined outside of Go), cannot inline it.
-	if len(fn.Body) == 0 {
+	// If a local function has no fn.Body (is defined outside of Go), cannot inline it.
+	// Imported functions don't have fn.Body but might have inline body in fn.Inl.
+	if len(fn.Body) == 0 && !typecheck.HaveInlineBody(fn) {
 		reason = "no function body"
 		return reason
 	}

src/cmd/compile/internal/test/pgo_devirtualize_test.go

@@ -57,11 +57,11 @@ go 1.19
 
 	want := []devirtualization{
 		{
-			pos:    "./devirt.go:81:21",
-			callee: "Mult.Multiply",
+			pos:    "./devirt.go:61:21",
+			callee: "mult.Mult.Multiply",
 		},
 		{
-			pos:    "./devirt.go:81:31",
+			pos:    "./devirt.go:61:31",
 			callee: "Add.Add",
 		},
 	}
@@ -115,8 +115,10 @@ func TestPGODevirtualize(t *testing.T) {
 
 	// Copy the module to a scratch location so we can add a go.mod.
 	dir := t.TempDir()
-
-	for _, file := range []string{"devirt.go", "devirt_test.go", "devirt.pprof"} {
+	if err := os.Mkdir(filepath.Join(dir, "mult"), 0755); err != nil {
+		t.Fatalf("error creating dir: %v", err)
+	}
+	for _, file := range []string{"devirt.go", "devirt_test.go", "devirt.pprof", filepath.Join("mult", "mult.go")} {
 		if err := copyFile(filepath.Join(dir, file), filepath.Join(srcDir, file)); err != nil {
 			t.Fatalf("error copying %s: %v", file, err)
 		}

src/cmd/compile/internal/test/testdata/pgo/devirtualize/devirt.go

@@ -11,32 +11,12 @@
 
 package devirt
 
-type Multiplier interface {
-	Multiply(a, b int) int
-}
-
-type Adder interface {
-	Add(a, b int) int
-}
+import "example.com/pgo/devirtualize/mult"
 
 var sink int
 
-type Mult struct{}
-
-func (Mult) Multiply(a, b int) int {
-	for i := 0; i < 1000; i++ {
-		sink++
-	}
-	return a * b
-}
-
-type NegMult struct{}
-
-func (NegMult) Multiply(a, b int) int {
-	for i := 0; i < 1000; i++ {
-		sink++
-	}
-	return -1 * a * b
+type Adder interface {
+	Add(a, b int) int
 }
 
 type Add struct{}
@@ -60,7 +40,7 @@ func (Sub) Add(a, b int) int {
 // Exercise calls mostly a1 and m1.
 //
 //go:noinline
-func Exercise(iter int, a1, a2 Adder, m1, m2 Multiplier) {
+func Exercise(iter int, a1, a2 Adder, m1, m2 mult.Multiplier) {
 	for i := 0; i < iter; i++ {
 		a := a1
 		m := m1
@@ -81,3 +61,13 @@ func Exercise(iter int, a1, a2 Adder, m1, m2 Multiplier) {
 		sink += m.Multiply(42, a.Add(1, 2))
 	}
 }
+
+func init() {
+	// TODO: until https://golang.org/cl/497175 or similar lands,
+	// we need to create an explicit reference to callees
+	// in another package for devirtualization to work.
+	m := mult.Mult{}
+	m.Multiply(42, 0)
+	n := mult.NegMult{}
+	n.Multiply(42, 0)
+}

src/cmd/compile/internal/test/testdata/pgo/devirtualize/devirt_test.go

@@ -13,14 +13,16 @@ package devirt
 
 import (
 	"testing"
+
+	"example.com/pgo/devirtualize/mult"
 )
 
 func BenchmarkDevirt(b *testing.B) {
 	var (
 		a1 Add
 		a2 Sub
-		m1 Mult
-		m2 NegMult
+		m1 mult.Mult
+		m2 mult.NegMult
 	)
 
 	Exercise(b.N, a1, a2, m1, m2)

src/cmd/compile/internal/test/testdata/pgo/devirtualize/mult/mult.go

@@ -0,0 +1,32 @@
+// Copyright 2023 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.
+
+// WARNING: Please avoid updating this file.
+// See the warning in ../devirt.go for more details.
+
+package mult
+
+var sink int
+
+type Multiplier interface {
+	Multiply(a, b int) int
+}
+
+type Mult struct{}
+
+func (Mult) Multiply(a, b int) int {
+	for i := 0; i < 1000; i++ {
+		sink++
+	}
+	return a * b
+}
+
+type NegMult struct{}
+
+func (NegMult) Multiply(a, b int) int {
+	for i := 0; i < 1000; i++ {
+		sink++
+	}
+	return -1 * a * b
+}