go/analysis/passes/atomicalign: handle pointers to struct

The atomicalign checker detects non-64-bit aligned struct field
arguments to sync/atomic functions but currently misses out cases
where the struct variable identifier is a pointer to struct. This
is very common as it happens when the 64-bit field is accessed
in a method with pointer receiver, where the struct is itself the
method receiver. Add some tests to cover that new case.

While I'm at it, fix some typos.

Change-Id: I582cf5b7286b11285010f085045f58dc636ef3ee
Reviewed-on: https://go-review.googlesource.com/c/158999
Reviewed-by: Alan Donovan <adonovan@google.com>

go/analysis/passes/atomicalign/atomicalign.go

@@ -21,7 +21,7 @@ import (
 
 var Analyzer = &analysis.Analyzer{
 	Name:     "atomicalign",
-	Doc:      "check for non-64-bits-aligned arguments to sync/atomic functions",
+	Doc:      "check for non-64-bit-aligned arguments to sync/atomic functions",
 	Requires: []*analysis.Analyzer{inspect.Analyzer},
 	Run:      run,
 }
@@ -70,7 +70,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 }
 
 func check64BitAlignment(pass *analysis.Pass, funcName string, arg ast.Expr) {
-	// Checks the argument is made of the address operator (&) applied to
+	// Checks the argument is made of the address operator (&) applied
 	// to a struct field (as opposed to a variable as the first word of
 	// uint64 and int64 variables can be relied upon to be 64-bit aligned.
 	unary, ok := arg.(*ast.UnaryExpr)
@@ -80,16 +80,18 @@ func check64BitAlignment(pass *analysis.Pass, funcName string, arg ast.Expr) {
 
 	// Retrieve the types.Struct in order to get the offset of the
 	// atomically accessed field.
-	sel, ok := unary.X.(*ast.SelectorExpr)
+	selector, ok := unary.X.(*ast.SelectorExpr)
 	if !ok {
 		return
 	}
-	tvar, ok := pass.TypesInfo.Selections[sel].Obj().(*types.Var)
+
+	sel := pass.TypesInfo.Selections[selector]
+	tvar, ok := sel.Obj().(*types.Var)
 	if !ok || !tvar.IsField() {
 		return
 	}
 
-	stype, ok := pass.TypesInfo.Types[sel.X].Type.Underlying().(*types.Struct)
+	stype, ok := sel.Recv().Underlying().(*types.Struct)
 	if !ok {
 		return
 	}

go/analysis/passes/atomicalign/testdata/src/a/a.go

@@ -228,3 +228,22 @@ func embeddedStructFields() {
 	atomic.AddUint64(&s1.b, 9) // want "address of non 64-bit aligned field .b passed to atomic.AddUint64"
 	atomic.AddInt64(&s1.c, 9)
 }
+
+type t struct {
+	_ int32
+	a int64
+	_ int16
+	_ int16
+	b uint64
+}
+
+func (t *t) structPointerReceiver() {
+	atomic.LoadInt64(&t.a) // want "address of non 64-bit aligned field .a passed to atomic.LoadInt64"
+	atomic.LoadUint64(&t.b)
+}
+
+func structPointer() {
+	t := &t{}
+	atomic.StoreInt64(&t.a, -1) // want "address of non 64-bit aligned field .a passed to atomic.StoreInt64"
+	atomic.StoreUint64(&t.b, 1)
+}