go/ssa: canonicalize receiver types to avoid creating duplicate thunk functions

+ test

Change-Id: Ie37835577ffcdd764cf6a0b611e02f04386755cf
Reviewed-on: https://go-review.googlesource.com/1580
Reviewed-by: Robert Griesemer <gri@golang.org>

4 files changed, 115 insertions, 5 deletions

diff --git a/go/ssa/builder_test.go b/go/ssa/builder_test.go
index 858db4b..aa6f319 100644
--- a/go/ssa/builder_test.go
+++ b/go/ssa/builder_test.go
@@ -13,6 +13,7 @@ import (
 
 	"golang.org/x/tools/go/loader"
 	"golang.org/x/tools/go/ssa"
+	"golang.org/x/tools/go/ssa/ssautil"
 	"golang.org/x/tools/go/types"
 )
 
@@ -317,3 +318,99 @@ func init():
 		}
 	}
 }
+
+// TestSyntheticFuncs checks that the expected synthetic functions are
+// created, reachable, and not duplicated.
+func TestSyntheticFuncs(t *testing.T) {
+	const input = `package P
+type T int
+func (T) f() int
+func (*T) g() int
+var (
+	// thunks
+	a = T.f
+	b = T.f
+	c = (struct{T}).f
+	d = (struct{T}).f
+	e = (*T).g
+	f = (*T).g
+	g = (struct{*T}).g
+	h = (struct{*T}).g
+
+	// bounds
+	i = T(0).f
+	j = T(0).f
+	k = new(T).g
+	l = new(T).g
+
+	// wrappers
+	m interface{} = struct{T}{}
+	n interface{} = struct{T}{}
+	o interface{} = struct{*T}{}
+	p interface{} = struct{*T}{}
+	q interface{} = new(struct{T})
+	r interface{} = new(struct{T})
+	s interface{} = new(struct{*T})
+	t interface{} = new(struct{*T})
+)
+`
+	// Parse
+	var conf loader.Config
+	f, err := conf.ParseFile("<input>", input)
+	if err != nil {
+		t.Fatalf("parse: %v", err)
+	}
+	conf.CreateFromFiles(f.Name.Name, f)
+
+	// Load
+	iprog, err := conf.Load()
+	if err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+
+	// Create and build SSA
+	prog := ssa.Create(iprog, 0)
+	prog.BuildAll()
+
+	// Enumerate reachable synthetic functions
+	want := map[string]string{
+		"(*P.T).g$bound": "bound method wrapper for func (*P.T).g() int",
+		"(P.T).f$bound":  "bound method wrapper for func (P.T).f() int",
+
+		"(*P.T).g$thunk":         "thunk for func (*P.T).g() int",
+		"(P.T).f$thunk":          "thunk for func (P.T).f() int",
+		"(struct{*P.T}).g$thunk": "thunk for func (*P.T).g() int",
+		"(struct{P.T}).f$thunk":  "thunk for func (P.T).f() int",
+
+		"(*P.T).f":          "wrapper for func (P.T).f() int",
+		"(*struct{*P.T}).f": "wrapper for func (P.T).f() int",
+		"(*struct{*P.T}).g": "wrapper for func (*P.T).g() int",
+		"(*struct{P.T}).f":  "wrapper for func (P.T).f() int",
+		"(*struct{P.T}).g":  "wrapper for func (*P.T).g() int",
+		"(struct{*P.T}).f":  "wrapper for func (P.T).f() int",
+		"(struct{*P.T}).g":  "wrapper for func (*P.T).g() int",
+		"(struct{P.T}).f":   "wrapper for func (P.T).f() int",
+
+		"P.init": "package initializer",
+	}
+	for fn := range ssautil.AllFunctions(prog) {
+		if fn.Synthetic == "" {
+			continue
+		}
+		name := fn.String()
+		wantDescr, ok := want[name]
+		if !ok {
+			t.Errorf("got unexpected/duplicate func: %q: %q", name, fn.Synthetic)
+			continue
+		}
+		delete(want, name)
+
+		if wantDescr != fn.Synthetic {
+			t.Errorf("(%s).Synthetic = %q, want %q",
+				name, fn.Synthetic, wantDescr)
+		}
+	}
+	for fn, descr := range want {
+		t.Errorf("want func: %q: %q", fn, descr)
+	}
+}
diff --git a/go/ssa/create.go b/go/ssa/create.go
index 7f57101..9b3a91b 100644
--- a/go/ssa/create.go
+++ b/go/ssa/create.go
@@ -15,6 +15,7 @@ import (
 
 	"golang.org/x/tools/go/loader"
 	"golang.org/x/tools/go/types"
+	"golang.org/x/tools/go/types/typeutil"
 )
 
 // BuilderMode is a bitmask of options for diagnostics and checking.
@@ -49,6 +50,10 @@ func Create(iprog *loader.Program, mode BuilderMode) *Program {
 		mode:     mode,
 	}
 
+	h := typeutil.MakeHasher() // protected by methodsMu, in effect
+	prog.methodSets.SetHasher(h)
+	prog.canon.SetHasher(h)
+
 	for _, info := range iprog.AllPackages {
 		// TODO(adonovan): relax this constraint if the
 		// program contains only "soft" errors.
diff --git a/go/ssa/ssa.go b/go/ssa/ssa.go
index 8543992..bc5e9da 100644
--- a/go/ssa/ssa.go
+++ b/go/ssa/ssa.go
@@ -30,6 +30,7 @@ type Program struct {
 
 	methodsMu  sync.Mutex                 // guards the following maps:
 	methodSets typeutil.Map               // maps type to its concrete methodSet
+	canon      typeutil.Map               // type canonicalization map
 	bounds     map[*types.Func]*Function  // bounds for curried x.Method closures
 	thunks     map[selectionKey]*Function // thunks for T.Method expressions
 }
diff --git a/go/ssa/wrappers.go b/go/ssa/wrappers.go
index 10c8a64..3c7e7f0 100644
--- a/go/ssa/wrappers.go
+++ b/go/ssa/wrappers.go
@@ -5,13 +5,13 @@
 package ssa
 
 // This file defines synthesis of Functions that delegate to declared
-// methods, which come in three kinds:
+// methods; they come in three kinds:
 //
 // (1) wrappers: methods that wrap declared methods, performing
 //     implicit pointer indirections and embedded field selections.
 //
 // (2) thunks: funcs that wrap declared methods.  Like wrappers,
-//     thunks perform indirections and field selections. The thunks's
+//     thunks perform indirections and field selections. The thunk's
 //     first parameter is used as the receiver for the method call.
 //
 // (3) bounds: funcs that wrap declared methods.  The bound's sole
@@ -250,8 +250,6 @@ func makeThunk(prog *Program, sel *types.Selection) *Function {
 		panic(sel)
 	}
 
-	// TODO(adonovan): opt: canonicalize the recv Type to avoid
-	// construct unnecessary duplicate thunks.
 	key := selectionKey{
 		kind:     sel.Kind(),
 		recv:     sel.Recv(),
@@ -262,6 +260,15 @@ func makeThunk(prog *Program, sel *types.Selection) *Function {
 
 	prog.methodsMu.Lock()
 	defer prog.methodsMu.Unlock()
+
+	// Canonicalize key.recv to avoid constructing duplicate thunks.
+	canonRecv, ok := prog.canon.At(key.recv).(types.Type)
+	if !ok {
+		canonRecv = key.recv
+		prog.canon.Set(key.recv, canonRecv)
+	}
+	key.recv = canonRecv
+
 	fn, ok := prog.thunks[key]
 	if !ok {
 		fn = makeWrapper(prog, sel)
@@ -280,7 +287,7 @@ func changeRecv(s *types.Signature, recv *types.Var) *types.Signature {
 // selectionKey is like types.Selection but a usable map key.
 type selectionKey struct {
 	kind     types.SelectionKind
-	recv     types.Type
+	recv     types.Type // canonicalized via Program.canon
 	obj      types.Object
 	index    string
 	indirect bool