1 // Copyright 2017 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 package x86
6 7 // argListMax specifies upper arg count limit expected to be carried by obj.Prog.
8 // Max len(obj.Prog.RestArgs) can be inferred from this to be 4.
9 const argListMax int = 6
10 11 type argList [argListMax]uint8
12 13 type ytab struct {
14 zcase uint8
15 zoffset uint8
16 17 // Last arg is usually destination.
18 // For unary instructions unaryDst is used to determine
19 // if single argument is a source or destination.
20 args argList
21 }
22 23 // Returns true if yt is compatible with args.
24 //
25 // Elements from args and yt.args are used
26 // to index ycover table like `ycover[args[i]+yt.args[i]]`.
27 // This means that args should contain values that already
28 // multiplied by Ymax.
29 func (yt *ytab) match(args []int) bool {
30 // Trailing Yxxx check is required to avoid a case
31 // where shorter arg list is matched.
32 // If we had exact yt.args length, it could be `yt.argc != len(args)`.
33 if len(args) < len(yt.args) && yt.args[len(args)] != Yxxx {
34 return false
35 }
36 37 for i := range args {
38 if ycover[args[i]+int(yt.args[i])] == 0 {
39 return false
40 }
41 }
42 43 return true
44 }
45