cmd/gc: don't hash nor compare struct padding or blank fields.
Fixes #4585.
R=rsc, golang-dev
CC=golang-dev
https://golang.org/cl/7142052
diff --git a/test/fixedbugs/issue4585.go b/test/fixedbugs/issue4585.go
new file mode 100644
index 0000000..558bd1e
--- /dev/null
+++ b/test/fixedbugs/issue4585.go
@@ -0,0 +1,91 @@
+// run
+
+// Copyright 2013 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.
+
+// Issue 4585: comparisons and hashes process blank
+// fields and padding in structs.
+
+package main
+
+import "unsafe"
+
+// T is a structure with padding.
+type T struct {
+ A int16
+ B int64
+ C int16
+ D int64
+ Dummy [64]byte
+}
+
+// U is a structure with a blank field
+type U struct {
+ A, _, B int
+ Dummy [64]byte
+}
+
+// USmall is like U but the frontend will inline comparison
+// instead of calling the generated eq function.
+type USmall struct {
+ A, _, B int32
+}
+
+func test1() {
+ var a, b U
+ m := make(map[U]int)
+ copy((*[16]byte)(unsafe.Pointer(&a))[:], "hello world!")
+ a.A, a.B = 1, 2
+ b.A, b.B = 1, 2
+ if a != b {
+ panic("broken equality: a != b")
+ }
+
+ m[a] = 1
+ m[b] = 2
+ if len(m) == 2 {
+ panic("broken hash: len(m) == 2")
+ }
+ if m[a] != 2 {
+ panic("m[a] != 2")
+ }
+}
+
+func test2() {
+ var a, b T
+ m := make(map[T]int)
+
+ copy((*[16]byte)(unsafe.Pointer(&a))[:], "hello world!")
+ a.A, a.B, a.C, a.D = 1, 2, 3, 4
+ b.A, b.B, b.C, b.D = 1, 2, 3, 4
+
+ if a != b {
+ panic("broken equality: a != b")
+ }
+
+ m[a] = 1
+ m[b] = 2
+ if len(m) == 2 {
+ panic("broken hash: len(m) == 2")
+ }
+ if m[a] != 2 {
+ panic("m[a] != 2")
+ }
+}
+
+func test3() {
+ var a, b USmall
+ copy((*[12]byte)(unsafe.Pointer(&a))[:], "hello world!")
+ a.A, a.B = 1, 2
+ b.A, b.B = 1, 2
+ if a != b {
+ panic("broken equality: a != b")
+ }
+}
+
+func main() {
+ test1()
+ test2()
+ test3()
+}
