location.go

     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/ir"
     9  	"cmd/compile/internal/types"
    10  	"fmt"
    11  )
    12  
    13  // A place that an ssa variable can reside.
    14  type Location interface {
    15  	String() string // name to use in assembly templates: AX, 16(SP), ...
    16  }
    17  
    18  // A Register is a machine register, like AX.
    19  // They are numbered densely from 0 (for each architecture).
    20  type Register struct {
    21  	num    int32 // dense numbering
    22  	objNum int16 // register number from cmd/internal/obj/$ARCH
    23  	gcNum  int16 // GC register map number (dense numbering of registers that can contain pointers)
    24  	name   string
    25  }
    26  
    27  func (r *Register) String() string {
    28  	return r.name
    29  }
    30  
    31  // ObjNum returns the register number from cmd/internal/obj/$ARCH that
    32  // corresponds to this register.
    33  func (r *Register) ObjNum() int16 {
    34  	return r.objNum
    35  }
    36  
    37  // GCNum returns the runtime GC register index of r, or -1 if this
    38  // register can't contain pointers.
    39  func (r *Register) GCNum() int16 {
    40  	return r.gcNum
    41  }
    42  
    43  // A LocalSlot is a location in the stack frame, which identifies and stores
    44  // part or all of a PPARAM, PPARAMOUT, or PAUTO ONAME node.
    45  // It can represent a whole variable, part of a larger stack slot, or part of a
    46  // variable that has been decomposed into multiple stack slots.
    47  // As an example, a string could have the following configurations:
    48  //
    49  //           stack layout              LocalSlots
    50  //
    51  // Optimizations are disabled. s is on the stack and represented in its entirety.
    52  // [ ------- s string ---- ] { N: s, Type: string, Off: 0 }
    53  //
    54  // s was not decomposed, but the SSA operates on its parts individually, so
    55  // there is a LocalSlot for each of its fields that points into the single stack slot.
    56  // [ ------- s string ---- ] { N: s, Type: *uint8, Off: 0 }, {N: s, Type: int, Off: 8}
    57  //
    58  // s was decomposed. Each of its fields is in its own stack slot and has its own LocalSLot.
    59  // [ ptr *uint8 ] [ len int] { N: ptr, Type: *uint8, Off: 0, SplitOf: parent, SplitOffset: 0},
    60  //                           { N: len, Type: int, Off: 0, SplitOf: parent, SplitOffset: 8}
    61  //                           parent = &{N: s, Type: string}
    62  type LocalSlot struct {
    63  	N    *ir.Name    // an ONAME *ir.Name representing a stack location.
    64  	Type *types.Type // type of slot
    65  	Off  int64       // offset of slot in N
    66  
    67  	SplitOf     *LocalSlot // slot is a decomposition of SplitOf
    68  	SplitOffset int64      // .. at this offset.
    69  }
    70  
    71  func (s LocalSlot) String() string {
    72  	if s.Off == 0 {
    73  		return fmt.Sprintf("%v[%v]", s.N, s.Type)
    74  	}
    75  	return fmt.Sprintf("%v+%d[%v]", s.N, s.Off, s.Type)
    76  }
    77  
    78  type LocPair [2]Location
    79  
    80  func (t LocPair) String() string {
    81  	n0, n1 := "nil", "nil"
    82  	if t[0] != nil {
    83  		n0 = t[0].String()
    84  	}
    85  	if t[1] != nil {
    86  		n1 = t[1].String()
    87  	}
    88  	return fmt.Sprintf("<%s,%s>", n0, n1)
    89  }
    90  
    91  type LocResults []Location
    92  
    93  func (t LocResults) String() string {
    94  	s := ""
    95  	a := "<"
    96  	for _, r := range t {
    97  		a += s
    98  		s = ","
    99  		a += r.String()
   100  	}
   101  	a += ">"
   102  	return a
   103  }
   104  
   105  type Spill struct {
   106  	Type   *types.Type
   107  	Offset int64
   108  	Reg    int16
   109  }
   110
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