asm,ir: add DwarfAttEncoding as valid DIExpressionField

Updates #101, #105.

asm/specialized_metadata.go

@@ -487,6 +487,8 @@ func (gen *generator) irDIExpressionField(old ast.DIExpressionField) (metadata.D
 	switch old := old.(type) {
 	case *ast.UintLit:
 		return metadata.UintLit(uintLit(*old)), nil
+	case *ast.DwarfAttEncodingEnum:
+		return asmenum.DwarfAttEncodingFromString(old.Text()), nil
 	case *ast.DwarfOp:
 		return asmenum.DwarfOpFromString(old.Text()), nil
 	default:

ir/enum/sumtype.go

@@ -2,6 +2,10 @@ package enum
 
 // === [ metadata.DIExpressionField ] ==========================================
 
+// IsDIExpressionField ensures that only DIExpression fields can be assigned to
+// the metadata.DIExpressionField interface.
+func (DwarfAttEncoding) IsDIExpressionField() {}
+
 // IsDIExpressionField ensures that only DIExpression fields can be assigned to
 // the metadata.DIExpressionField interface.
 func (DwarfOp) IsDIExpressionField() {}

ir/metadata/sumtypes.go

@@ -110,8 +110,9 @@ type FieldOrInt interface {
 //
 // A DIExpressionField has one of the following underlying types.
 //
-//    metadata.UintLit   // https://godoc.org/github.com/llir/llvm/ir/metadata#UintLit
-//    enum.DwarfOp       // https://godoc.org/github.com/llir/llvm/ir/enum#DwarfOp
+//    metadata.UintLit        // https://godoc.org/github.com/llir/llvm/ir/metadata#UintLit
+//    enum.DwarfAttEncoding   // https://godoc.org/github.com/llir/llvm/ir/enum#DwarfAttEncoding
+//    enum.DwarfOp            // https://godoc.org/github.com/llir/llvm/ir/enum#DwarfOp
 type DIExpressionField interface {
 	fmt.Stringer
 	// IsDIExpressionField ensures that only DIExpression fields can be assigned