github.com/corona10/go@v0.0.0-20180224231303-7a218942be57/src/cmd/compile/internal/ssa/location.go (about)

     1  // Copyright 2015 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 ssa
     6  
     7  import (
     8  	"cmd/compile/internal/types"
     9  	"fmt"
    10  )
    11  
    12  // A place that an ssa variable can reside.
    13  type Location interface {
    14  	String() string // name to use in assembly templates: AX, 16(SP), ...
    15  }
    16  
    17  // A Register is a machine register, like AX.
    18  // They are numbered densely from 0 (for each architecture).
    19  type Register struct {
    20  	num    int32 // dense numbering
    21  	objNum int16 // register number from cmd/internal/obj/$ARCH
    22  	name   string
    23  }
    24  
    25  func (r *Register) String() string {
    26  	return r.name
    27  }
    28  
    29  // ObjNum returns the register number from cmd/internal/obj/$ARCH that
    30  // corresponds to this register.
    31  func (r *Register) ObjNum() int16 {
    32  	return r.objNum
    33  }
    34  
    35  // A LocalSlot is a location in the stack frame, which identifies and stores
    36  // part or all of a PPARAM, PPARAMOUT, or PAUTO ONAME node.
    37  // It can represent a whole variable, part of a larger stack slot, or part of a
    38  // variable that has been decomposed into multiple stack slots.
    39  // As an example, a string could have the following configurations:
    40  //
    41  //           stack layout              LocalSlots
    42  //
    43  // Optimizations are disabled. s is on the stack and represented in its entirety.
    44  // [ ------- s string ---- ] { N: s, Type: string, Off: 0 }
    45  //
    46  // s was not decomposed, but the SSA operates on its parts individually, so
    47  // there is a LocalSlot for each of its fields that points into the single stack slot.
    48  // [ ------- s string ---- ] { N: s, Type: *uint8, Off: 0 }, {N: s, Type: int, Off: 8}
    49  //
    50  // s was decomposed. Each of its fields is in its own stack slot and has its own LocalSLot.
    51  // [ ptr *uint8 ] [ len int] { N: ptr, Type: *uint8, Off: 0, SplitOf: parent, SplitOffset: 0},
    52  //                           { N: len, Type: int, Off: 0, SplitOf: parent, SplitOffset: 8}
    53  //                           parent = &{N: s, Type: string}
    54  type LocalSlot struct {
    55  	N    GCNode      // an ONAME *gc.Node representing a stack location.
    56  	Type *types.Type // type of slot
    57  	Off  int64       // offset of slot in N
    58  
    59  	SplitOf     *LocalSlot // slot is a decomposition of SplitOf
    60  	SplitOffset int64      // .. at this offset.
    61  }
    62  
    63  func (s LocalSlot) String() string {
    64  	if s.Off == 0 {
    65  		return fmt.Sprintf("%v[%v]", s.N, s.Type)
    66  	}
    67  	return fmt.Sprintf("%v+%d[%v]", s.N, s.Off, s.Type)
    68  }
    69  
    70  type LocPair [2]Location
    71  
    72  func (t LocPair) String() string {
    73  	n0, n1 := "nil", "nil"
    74  	if t[0] != nil {
    75  		n0 = t[0].String()
    76  	}
    77  	if t[1] != nil {
    78  		n1 = t[1].String()
    79  	}
    80  	return fmt.Sprintf("<%s,%s>", n0, n1)
    81  }