ytab.go

     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
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