all: change special type __volatile to pragma //go:volatile

This is one step towards removing unnecessary special casts in most
cases. It is also part of removing as much magic as possible from the
compiler (the pragma is explicit, the special name is not).

ir/ir.go

@@ -90,15 +90,20 @@ func NewProgram(lprogram *loader.Program, mainPath string) *Program {
 				switch decl := decl.(type) {
 				case *ast.GenDecl:
 					switch decl.Tok {
-					case token.VAR:
+					case token.TYPE, token.VAR:
 						if len(decl.Specs) != 1 {
 							continue
 						}
 						for _, spec := range decl.Specs {
-							valueSpec := spec.(*ast.ValueSpec)
-							for _, valueName := range valueSpec.Names {
-								id := pkgInfo.Pkg.Path() + "." + valueName.Name
+							switch spec := spec.(type) {
+							case *ast.TypeSpec: // decl.Tok == token.TYPE
+								id := pkgInfo.Pkg.Path() + "." + spec.Name.Name
 								comments[id] = decl.Doc
+							case *ast.ValueSpec: // decl.Tok == token.VAR
+								for _, name := range spec.Names {
+									id := pkgInfo.Pkg.Path() + "." + name.Name
+									comments[id] = decl.Doc
+								}
 							}
 						}
 					}
@@ -414,6 +419,26 @@ func (g *Global) Initializer() Value {
 	return g.initializer
 }
 
+// Return true if this named type is annotated with the //go:volatile pragma,
+// for volatile loads and stores.
+func (p *Program) IsVolatile(t types.Type) bool {
+	if t, ok := t.(*types.Named); !ok {
+		return false
+	} else {
+		id := t.Obj().Pkg().Path() + "." + t.Obj().Name()
+		doc := p.comments[id]
+		if doc == nil {
+			return false
+		}
+		for _, line := range doc.List {
+			if strings.TrimSpace(line.Text) == "//go:volatile" {
+				return true
+			}
+		}
+		return false
+	}
+}
+
 // Wrapper type to implement sort.Interface for []*types.Selection.
 type methodList struct {
 	methods []*types.Selection