go/types: remove struct Sizeof cache

It was not responsive to the sizes param.
Remove it, and unwind the extra layers.

Fixes #16316

Change-Id: I940a57184a1601f52348d4bff8638f3f7462f5cd
Reviewed-on: https://go-review.googlesource.com/26995
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/sizes.go

@@ -132,8 +132,8 @@ func (s *StdSizes) Sizeof(T Type) int64 {
 		if n == 0 {
 			return 0
 		}
-		setOffsets(t, s)
-		return t.offsets[n-1] + s.Sizeof(t.fields[n-1].typ)
+		offsets := s.Offsetsof(t.fields)
+		return offsets[n-1] + s.Sizeof(t.fields[n-1].typ)
 	case *Interface:
 		return s.WordSize * 2
 	}
@@ -158,22 +158,18 @@ func (conf *Config) offsetsof(T *Struct) []int64 {
 	if T.NumFields() > 0 {
 		// compute offsets on demand
 		if s := conf.Sizes; s != nil {
-			calculated := setOffsets(T, s)
-			offsets = T.offsets
-			if calculated {
-				// sanity checks
-				if len(offsets) != T.NumFields() {
-					panic("Config.Sizes.Offsetsof returned the wrong number of offsets")
-				}
-				for _, o := range offsets {
-					if o < 0 {
-						panic("Config.Sizes.Offsetsof returned an offset < 0")
-					}
+			offsets := s.Offsetsof(T.fields)
+			// sanity checks
+			if len(offsets) != T.NumFields() {
+				panic("Config.Sizes.Offsetsof returned the wrong number of offsets")
+			}
+			for _, o := range offsets {
+				if o < 0 {
+					panic("Config.Sizes.Offsetsof returned an offset < 0")
 				}
 			}
 		} else {
-			setOffsets(T, &stdSizes)
-			offsets = T.offsets
+			offsets = stdSizes.Offsetsof(T.fields)
 		}
 	}
 	return offsets
@@ -207,15 +203,3 @@ func align(x, a int64) int64 {
 	y := x + a - 1
 	return y - y%a
 }
-
-// setOffsets sets the offsets of s for the given sizes if necessary.
-// The result is true if the offsets were not set before; otherwise it
-// is false.
-func setOffsets(s *Struct, sizes Sizes) bool {
-	var calculated bool
-	s.offsetsOnce.Do(func() {
-		calculated = true
-		s.offsets = sizes.Offsetsof(s.fields)
-	})
-	return calculated
-}

src/go/types/sizes_test.go

+// Copyright 2016 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.
+
+// This file contains tests for sizes.
+
+package types_test
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"go/types"
+	"testing"
+)
+
+// findStructType typechecks src and returns the first struct type encountered.
+func findStructType(t *testing.T, src string) *types.Struct {
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, "x.go", src, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	info := types.Info{Types: make(map[ast.Expr]types.TypeAndValue)}
+	var conf types.Config
+	_, err = conf.Check("x", fset, []*ast.File{f}, &info)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, tv := range info.Types {
+		if ts, ok := tv.Type.(*types.Struct); ok {
+			return ts
+		}
+	}
+	t.Fatalf("failed to find a struct type in src:\n%s\n", src)
+	return nil
+}
+
+// Issue 16316
+func TestMultipleSizeUse(t *testing.T) {
+	const src = `
+package main
+
+type S struct {
+    i int
+    b bool
+    s string
+    n int
+}
+`
+	ts := findStructType(t, src)
+	sizes := types.StdSizes{WordSize: 4, MaxAlign: 4}
+	if got := sizes.Sizeof(ts); got != 20 {
+		t.Errorf("Sizeof(%v) with WordSize 4 = %d want 20", ts, got)
+	}
+	sizes = types.StdSizes{WordSize: 8, MaxAlign: 8}
+	if got := sizes.Sizeof(ts); got != 40 {
+		t.Errorf("Sizeof(%v) with WordSize 8 = %d want 40", ts, got)
+	}
+}

src/go/types/type.go

@@ -4,10 +4,7 @@
 
 package types
 
-import (
-	"sort"
-	"sync"
-)
+import "sort"
 
 // A Type represents a type of Go.
 // All types implement the Type interface.
@@ -121,10 +118,8 @@ func (s *Slice) Elem() Type { return s.elem }
 
 // A Struct represents a struct type.
 type Struct struct {
-	fields      []*Var
-	tags        []string  // field tags; nil if there are no tags
-	offsets     []int64   // field offsets in bytes, lazily initialized
-	offsetsOnce sync.Once // for threadsafe lazy initialization of offsets
+	fields []*Var
+	tags   []string // field tags; nil if there are no tags
 }
 
 // NewStruct returns a new struct with the given fields and corresponding field tags.