src/cmd/compile/internal/ssa/op.go - go - Git at Google

 // Copyright 2015 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package ssa

 import (
 	"cmd/compile/internal/types"
 	"cmd/internal/obj"
 	"fmt"
 )

 // An Op encodes the specific operation that a Value performs.
 // Opcodes' semantics can be modified by the type and aux fields of the Value.
 // For instance, OpAdd can be 32 or 64 bit, signed or unsigned, float or complex, depending on Value.Type.
 // Semantics of each op are described in the opcode files in gen/*Ops.go.
 // There is one file for generic (architecture-independent) ops and one file
 // for each architecture.
 type Op int32

 type opInfo struct {
 	name              string
 	reg               regInfo
 	auxType           auxType
 	argLen            int32 // the number of arguments, -1 if variable length
 	asm               obj.As
 	generic           bool      // this is a generic (arch-independent) opcode
 	rematerializeable bool      // this op is rematerializeable
 	commutative       bool      // this operation is commutative (e.g. addition)
 	resultInArg0      bool      // (first, if a tuple) output of v and v.Args[0] must be allocated to the same register
 	resultNotInArgs   bool      // outputs must not be allocated to the same registers as inputs
 	clobberFlags      bool      // this op clobbers flags register
 	call              bool      // is a function call
 	nilCheck          bool      // this op is a nil check on arg0
 	faultOnNilArg0    bool      // this op will fault if arg0 is nil (and aux encodes a small offset)
 	faultOnNilArg1    bool      // this op will fault if arg1 is nil (and aux encodes a small offset)
 	usesScratch       bool      // this op requires scratch memory space
 	hasSideEffects    bool      // for "reasons", not to be eliminated.  E.g., atomic store, #19182.
 	zeroWidth         bool      // op never translates into any machine code. example: copy, which may sometimes translate to machine code, is not zero-width.
 	unsafePoint       bool      // this op is an unsafe point, i.e. not safe for async preemption
 	symEffect         SymEffect // effect this op has on symbol in aux
 	scale             uint8     // amd64/386 indexed load scale
 }

 type inputInfo struct {
 	idx  int     // index in Args array
 	regs regMask // allowed input registers
 }

 type outputInfo struct {
 	idx  int     // index in output tuple
 	regs regMask // allowed output registers
 }

 type regInfo struct {
 	// inputs encodes the register restrictions for an instruction's inputs.
 	// Each entry specifies an allowed register set for a particular input.
 	// They are listed in the order in which regalloc should pick a register
 	// from the register set (most constrained first).
 	// Inputs which do not need registers are not listed.
 	inputs []inputInfo
 	// clobbers encodes the set of registers that are overwritten by
 	// the instruction (other than the output registers).
 	clobbers regMask
 	// outputs is the same as inputs, but for the outputs of the instruction.
 	outputs []outputInfo
 }

 type auxType int8

 type Param struct {
 	Type   *types.Type
 	Offset int32 // TODO someday this will be a register
 }

 type AuxCall struct {
 	Fn      *obj.LSym
 	args    []Param // Includes receiver for method calls.  Does NOT include hidden closure pointer.
 	results []Param
 }

 func (a *AuxCall) String() string {
 	var fn string
 	if a.Fn == nil {
 		fn = "AuxCall{nil" // could be interface/closure etc.
 	} else {
 		fn = fmt.Sprintf("AuxCall{%v", a.Fn)
 	}

 	if len(a.args) == 0 {
 		fn += "()"
 	} else {
 		s := "("
 		for _, arg := range a.args {
 			fn += fmt.Sprintf("%s[%v,%v]", s, arg.Type, arg.Offset)
 			s = ","
 		}
 		fn += ")"
 	}

 	if len(a.results) > 0 { // usual is zero or one; only some RT calls have more than one.
 		if len(a.results) == 1 {
 			fn += fmt.Sprintf("[%v,%v]", a.results[0].Type, a.results[0].Offset)
 		} else {
 			s := "("
 			for _, result := range a.results {
 				fn += fmt.Sprintf("%s[%v,%v]", s, result.Type, result.Offset)
 				s = ","
 			}
 			fn += ")"
 		}
 	}

 	return fn + "}"
 }

 // StaticAuxCall returns an AuxCall for a static call.
 func StaticAuxCall(sym *obj.LSym, args []Param, results []Param) *AuxCall {
 	return &AuxCall{Fn: sym, args: args, results: results}
 }

 // InterfaceAuxCall returns an AuxCall for an interface call.
 func InterfaceAuxCall(args []Param, results []Param) *AuxCall {
 	return &AuxCall{Fn: nil, args: args, results: results}
 }

 // ClosureAuxCall returns an AuxCall for a closure call.
 func ClosureAuxCall() *AuxCall {
 	return &AuxCall{}
 }

 const (
 	auxNone         auxType = iota
 	auxBool                 // auxInt is 0/1 for false/true
 	auxInt8                 // auxInt is an 8-bit integer
 	auxInt16                // auxInt is a 16-bit integer
 	auxInt32                // auxInt is a 32-bit integer
 	auxInt64                // auxInt is a 64-bit integer
 	auxInt128               // auxInt represents a 128-bit integer.  Always 0.
 	auxFloat32              // auxInt is a float32 (encoded with math.Float64bits)
 	auxFloat64              // auxInt is a float64 (encoded with math.Float64bits)
 	auxFlagConstant         // auxInt is a flagConstant
 	auxString               // aux is a string
 	auxSym                  // aux is a symbol (a *gc.Node for locals, an *obj.LSym for globals, or nil for none)
 	auxSymOff               // aux is a symbol, auxInt is an offset
 	auxSymValAndOff         // aux is a symbol, auxInt is a ValAndOff
 	auxTyp                  // aux is a type
 	auxTypSize              // aux is a type, auxInt is a size, must have Aux.(Type).Size() == AuxInt
 	auxCCop                 // aux is a ssa.Op that represents a flags-to-bool conversion (e.g. LessThan)
 	auxCall                 // aux is a *ssa.AuxCall
 	auxCallOff              // aux is a *ssa.AuxCall, AuxInt is int64 param (in+out) size

 	// architecture specific aux types
 	auxARM64BitField     // aux is an arm64 bitfield lsb and width packed into auxInt
 	auxS390XRotateParams // aux is a s390x rotate parameters object encoding start bit, end bit and rotate amount
 	auxS390XCCMask       // aux is a s390x 4-bit condition code mask
 	auxS390XCCMaskInt8   // aux is a s390x 4-bit condition code mask, auxInt is a int8 immediate
 	auxS390XCCMaskUint8  // aux is a s390x 4-bit condition code mask, auxInt is a uint8 immediate
 )

 // A SymEffect describes the effect that an SSA Value has on the variable
 // identified by the symbol in its Aux field.
 type SymEffect int8

 const (
 	SymRead SymEffect = 1 << iota
 	SymWrite
 	SymAddr

 	SymRdWr = SymRead | SymWrite

 	SymNone SymEffect = 0
 )

 // A Sym represents a symbolic offset from a base register.
 // Currently a Sym can be one of 3 things:
 //  - a *gc.Node, for an offset from SP (the stack pointer)
 //  - a *obj.LSym, for an offset from SB (the global pointer)
 //  - nil, for no offset
 type Sym interface {
 	String() string
 	CanBeAnSSASym()
 }

 // A ValAndOff is used by the several opcodes. It holds
 // both a value and a pointer offset.
 // A ValAndOff is intended to be encoded into an AuxInt field.
 // The zero ValAndOff encodes a value of 0 and an offset of 0.
 // The high 32 bits hold a value.
 // The low 32 bits hold a pointer offset.
 type ValAndOff int64

 func (x ValAndOff) Val() int64   { return int64(x) >> 32 }
 func (x ValAndOff) Val32() int32 { return int32(int64(x) >> 32) }
 func (x ValAndOff) Val16() int16 { return int16(int64(x) >> 32) }
 func (x ValAndOff) Val8() int8   { return int8(int64(x) >> 32) }

 func (x ValAndOff) Off() int64   { return int64(int32(x)) }
 func (x ValAndOff) Off32() int32 { return int32(x) }

 func (x ValAndOff) Int64() int64 {
 	return int64(x)
 }
 func (x ValAndOff) String() string {
 	return fmt.Sprintf("val=%d,off=%d", x.Val(), x.Off())
 }

 // validVal reports whether the value can be used
 // as an argument to makeValAndOff.
 func validVal(val int64) bool {
 	return val == int64(int32(val))
 }

 // validOff reports whether the offset can be used
 // as an argument to makeValAndOff.
 func validOff(off int64) bool {
 	return off == int64(int32(off))
 }

 // validValAndOff reports whether we can fit the value and offset into
 // a ValAndOff value.
 func validValAndOff(val, off int64) bool {
 	if !validVal(val) {
 		return false
 	}
 	if !validOff(off) {
 		return false
 	}
 	return true
 }

 // makeValAndOff encodes a ValAndOff into an int64 suitable for storing in an AuxInt field.
 func makeValAndOff(val, off int64) int64 {
 	if !validValAndOff(val, off) {
 		panic("invalid makeValAndOff")
 	}
 	return ValAndOff(val<<32 + int64(uint32(off))).Int64()
 }
 func makeValAndOff32(val, off int32) ValAndOff {
 	return ValAndOff(int64(val)<<32 + int64(uint32(off)))
 }

 func (x ValAndOff) canAdd(off int64) bool {
 	newoff := x.Off() + off
 	return newoff == int64(int32(newoff))
 }

 func (x ValAndOff) canAdd32(off int32) bool {
 	newoff := x.Off() + int64(off)
 	return newoff == int64(int32(newoff))
 }

 func (x ValAndOff) add(off int64) int64 {
 	if !x.canAdd(off) {
 		panic("invalid ValAndOff.add")
 	}
 	return makeValAndOff(x.Val(), x.Off()+off)
 }

 func (x ValAndOff) addOffset32(off int32) ValAndOff {
 	if !x.canAdd32(off) {
 		panic("invalid ValAndOff.add")
 	}
 	return ValAndOff(makeValAndOff(x.Val(), x.Off()+int64(off)))
 }

 func (x ValAndOff) addOffset64(off int64) ValAndOff {
 	if !x.canAdd(off) {
 		panic("invalid ValAndOff.add")
 	}
 	return ValAndOff(makeValAndOff(x.Val(), x.Off()+off))
 }

 // int128 is a type that stores a 128-bit constant.
 // The only allowed constant right now is 0, so we can cheat quite a bit.
 type int128 int64

 type BoundsKind uint8

 const (
 	BoundsIndex       BoundsKind = iota // indexing operation, 0 <= idx < len failed
 	BoundsIndexU                        // ... with unsigned idx
 	BoundsSliceAlen                     // 2-arg slicing operation, 0 <= high <= len failed
 	BoundsSliceAlenU                    // ... with unsigned high
 	BoundsSliceAcap                     // 2-arg slicing operation, 0 <= high <= cap failed
 	BoundsSliceAcapU                    // ... with unsigned high
 	BoundsSliceB                        // 2-arg slicing operation, 0 <= low <= high failed
 	BoundsSliceBU                       // ... with unsigned low
 	BoundsSlice3Alen                    // 3-arg slicing operation, 0 <= max <= len failed
 	BoundsSlice3AlenU                   // ... with unsigned max
 	BoundsSlice3Acap                    // 3-arg slicing operation, 0 <= max <= cap failed
 	BoundsSlice3AcapU                   // ... with unsigned max
 	BoundsSlice3B                       // 3-arg slicing operation, 0 <= high <= max failed
 	BoundsSlice3BU                      // ... with unsigned high
 	BoundsSlice3C                       // 3-arg slicing operation, 0 <= low <= high failed
 	BoundsSlice3CU                      // ... with unsigned low
 	BoundsKindCount
 )

 // boundsAPI determines which register arguments a bounds check call should use. For an [a:b:c] slice, we do:
 //   CMPQ c, cap
 //   JA   fail1
 //   CMPQ b, c
 //   JA   fail2
 //   CMPQ a, b
 //   JA   fail3
 //
 // fail1: CALL panicSlice3Acap (c, cap)
 // fail2: CALL panicSlice3B (b, c)
 // fail3: CALL panicSlice3C (a, b)
 //
 // When we register allocate that code, we want the same register to be used for
 // the first arg of panicSlice3Acap and the second arg to panicSlice3B. That way,
 // initializing that register once will satisfy both calls.
 // That desire ends up dividing the set of bounds check calls into 3 sets. This function
 // determines which set to use for a given panic call.
 // The first arg for set 0 should be the second arg for set 1.
 // The first arg for set 1 should be the second arg for set 2.
 func boundsABI(b int64) int {
 	switch BoundsKind(b) {
 	case BoundsSlice3Alen,
 		BoundsSlice3AlenU,
 		BoundsSlice3Acap,
 		BoundsSlice3AcapU:
 		return 0
 	case BoundsSliceAlen,
 		BoundsSliceAlenU,
 		BoundsSliceAcap,
 		BoundsSliceAcapU,
 		BoundsSlice3B,
 		BoundsSlice3BU:
 		return 1
 	case BoundsIndex,
 		BoundsIndexU,
 		BoundsSliceB,
 		BoundsSliceBU,
 		BoundsSlice3C,
 		BoundsSlice3CU:
 		return 2
 	default:
 		panic("bad BoundsKind")
 	}
 }

 // arm64BitFileld is the GO type of ARM64BitField auxInt.
 // if x is an ARM64BitField, then width=x&0xff, lsb=(x>>8)&0xff, and
 // width+lsb<64 for 64-bit variant, width+lsb<32 for 32-bit variant.
 // the meaning of width and lsb are instruction-dependent.
 type arm64BitField int16
	// Copyright 2015 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package ssa

	import (
	"cmd/compile/internal/types"
	"cmd/internal/obj"
	"fmt"
	)

	// An Op encodes the specific operation that a Value performs.
	// Opcodes' semantics can be modified by the type and aux fields of the Value.
	// For instance, OpAdd can be 32 or 64 bit, signed or unsigned, float or complex, depending on Value.Type.
	// Semantics of each op are described in the opcode files in gen/*Ops.go.
	// There is one file for generic (architecture-independent) ops and one file
	// for each architecture.
	type Op int32

	type opInfo struct {
	name string
	reg regInfo
	auxType auxType
	argLen int32 // the number of arguments, -1 if variable length
	asm obj.As
	generic bool // this is a generic (arch-independent) opcode
	rematerializeable bool // this op is rematerializeable
	commutative bool // this operation is commutative (e.g. addition)
	resultInArg0 bool // (first, if a tuple) output of v and v.Args[0] must be allocated to the same register
	resultNotInArgs bool // outputs must not be allocated to the same registers as inputs
	clobberFlags bool // this op clobbers flags register
	call bool // is a function call
	nilCheck bool // this op is a nil check on arg0
	faultOnNilArg0 bool // this op will fault if arg0 is nil (and aux encodes a small offset)
	faultOnNilArg1 bool // this op will fault if arg1 is nil (and aux encodes a small offset)
	usesScratch bool // this op requires scratch memory space
	hasSideEffects bool // for "reasons", not to be eliminated. E.g., atomic store, #19182.
	zeroWidth bool // op never translates into any machine code. example: copy, which may sometimes translate to machine code, is not zero-width.
	unsafePoint bool // this op is an unsafe point, i.e. not safe for async preemption
	symEffect SymEffect // effect this op has on symbol in aux
	scale uint8 // amd64/386 indexed load scale
	}

	type inputInfo struct {
	idx int // index in Args array
	regs regMask // allowed input registers
	}

	type outputInfo struct {
	idx int // index in output tuple
	regs regMask // allowed output registers
	}

	type regInfo struct {
	// inputs encodes the register restrictions for an instruction's inputs.
	// Each entry specifies an allowed register set for a particular input.
	// They are listed in the order in which regalloc should pick a register
	// from the register set (most constrained first).
	// Inputs which do not need registers are not listed.
	inputs []inputInfo
	// clobbers encodes the set of registers that are overwritten by
	// the instruction (other than the output registers).
	clobbers regMask
	// outputs is the same as inputs, but for the outputs of the instruction.
	outputs []outputInfo
	}

	type auxType int8

	type Param struct {
	Type *types.Type
	Offset int32 // TODO someday this will be a register
	}

	type AuxCall struct {
	Fn *obj.LSym
	args []Param // Includes receiver for method calls. Does NOT include hidden closure pointer.
	results []Param
	}

	func (a *AuxCall) String() string {
	var fn string
	if a.Fn == nil {
	fn = "AuxCall{nil" // could be interface/closure etc.
	} else {
	fn = fmt.Sprintf("AuxCall{%v", a.Fn)
	}

	if len(a.args) == 0 {
	fn += "()"
	} else {
	s := "("
	for _, arg := range a.args {
	fn += fmt.Sprintf("%s[%v,%v]", s, arg.Type, arg.Offset)
	s = ","
	}
	fn += ")"
	}

	if len(a.results) > 0 { // usual is zero or one; only some RT calls have more than one.
	if len(a.results) == 1 {
	fn += fmt.Sprintf("[%v,%v]", a.results[0].Type, a.results[0].Offset)
	} else {
	s := "("
	for _, result := range a.results {
	fn += fmt.Sprintf("%s[%v,%v]", s, result.Type, result.Offset)
	s = ","
	}
	fn += ")"
	}
	}

	return fn + "}"
	}

	// StaticAuxCall returns an AuxCall for a static call.
	func StaticAuxCall(sym obj.LSym, args []Param, results []Param) AuxCall {
	return &AuxCall{Fn: sym, args: args, results: results}
	}

	// InterfaceAuxCall returns an AuxCall for an interface call.
	func InterfaceAuxCall(args []Param, results []Param) *AuxCall {
	return &AuxCall{Fn: nil, args: args, results: results}
	}

	// ClosureAuxCall returns an AuxCall for a closure call.
	func ClosureAuxCall() *AuxCall {
	return &AuxCall{}
	}

	const (
	auxNone auxType = iota
	auxBool // auxInt is 0/1 for false/true
	auxInt8 // auxInt is an 8-bit integer
	auxInt16 // auxInt is a 16-bit integer
	auxInt32 // auxInt is a 32-bit integer
	auxInt64 // auxInt is a 64-bit integer
	auxInt128 // auxInt represents a 128-bit integer. Always 0.
	auxFloat32 // auxInt is a float32 (encoded with math.Float64bits)
	auxFloat64 // auxInt is a float64 (encoded with math.Float64bits)
	auxFlagConstant // auxInt is a flagConstant
	auxString // aux is a string
	auxSym // aux is a symbol (a gc.Node for locals, an obj.LSym for globals, or nil for none)
	auxSymOff // aux is a symbol, auxInt is an offset
	auxSymValAndOff // aux is a symbol, auxInt is a ValAndOff
	auxTyp // aux is a type
	auxTypSize // aux is a type, auxInt is a size, must have Aux.(Type).Size() == AuxInt
	auxCCop // aux is a ssa.Op that represents a flags-to-bool conversion (e.g. LessThan)
	auxCall // aux is a *ssa.AuxCall
	auxCallOff // aux is a *ssa.AuxCall, AuxInt is int64 param (in+out) size

	// architecture specific aux types
	auxARM64BitField // aux is an arm64 bitfield lsb and width packed into auxInt
	auxS390XRotateParams // aux is a s390x rotate parameters object encoding start bit, end bit and rotate amount
	auxS390XCCMask // aux is a s390x 4-bit condition code mask
	auxS390XCCMaskInt8 // aux is a s390x 4-bit condition code mask, auxInt is a int8 immediate
	auxS390XCCMaskUint8 // aux is a s390x 4-bit condition code mask, auxInt is a uint8 immediate
	)

	// A SymEffect describes the effect that an SSA Value has on the variable
	// identified by the symbol in its Aux field.
	type SymEffect int8

	const (
	SymRead SymEffect = 1 << iota
	SymWrite
	SymAddr

	SymRdWr = SymRead \| SymWrite

	SymNone SymEffect = 0
	)

	// A Sym represents a symbolic offset from a base register.
	// Currently a Sym can be one of 3 things:
	// - a *gc.Node, for an offset from SP (the stack pointer)
	// - a *obj.LSym, for an offset from SB (the global pointer)
	// - nil, for no offset
	type Sym interface {
	String() string
	CanBeAnSSASym()
	}

	// A ValAndOff is used by the several opcodes. It holds
	// both a value and a pointer offset.
	// A ValAndOff is intended to be encoded into an AuxInt field.
	// The zero ValAndOff encodes a value of 0 and an offset of 0.
	// The high 32 bits hold a value.
	// The low 32 bits hold a pointer offset.
	type ValAndOff int64

	func (x ValAndOff) Val() int64 { return int64(x) >> 32 }
	func (x ValAndOff) Val32() int32 { return int32(int64(x) >> 32) }
	func (x ValAndOff) Val16() int16 { return int16(int64(x) >> 32) }
	func (x ValAndOff) Val8() int8 { return int8(int64(x) >> 32) }

	func (x ValAndOff) Off() int64 { return int64(int32(x)) }
	func (x ValAndOff) Off32() int32 { return int32(x) }

	func (x ValAndOff) Int64() int64 {
	return int64(x)
	}
	func (x ValAndOff) String() string {
	return fmt.Sprintf("val=%d,off=%d", x.Val(), x.Off())
	}

	// validVal reports whether the value can be used
	// as an argument to makeValAndOff.
	func validVal(val int64) bool {
	return val == int64(int32(val))
	}

	// validOff reports whether the offset can be used
	// as an argument to makeValAndOff.
	func validOff(off int64) bool {
	return off == int64(int32(off))
	}

	// validValAndOff reports whether we can fit the value and offset into
	// a ValAndOff value.
	func validValAndOff(val, off int64) bool {
	if !validVal(val) {
	return false
	}
	if !validOff(off) {
	return false
	}
	return true
	}

	// makeValAndOff encodes a ValAndOff into an int64 suitable for storing in an AuxInt field.
	func makeValAndOff(val, off int64) int64 {
	if !validValAndOff(val, off) {
	panic("invalid makeValAndOff")
	}
	return ValAndOff(val<<32 + int64(uint32(off))).Int64()
	}
	func makeValAndOff32(val, off int32) ValAndOff {
	return ValAndOff(int64(val)<<32 + int64(uint32(off)))
	}

	func (x ValAndOff) canAdd(off int64) bool {
	newoff := x.Off() + off
	return newoff == int64(int32(newoff))
	}

	func (x ValAndOff) canAdd32(off int32) bool {
	newoff := x.Off() + int64(off)
	return newoff == int64(int32(newoff))
	}

	func (x ValAndOff) add(off int64) int64 {
	if !x.canAdd(off) {
	panic("invalid ValAndOff.add")
	}
	return makeValAndOff(x.Val(), x.Off()+off)
	}

	func (x ValAndOff) addOffset32(off int32) ValAndOff {
	if !x.canAdd32(off) {
	panic("invalid ValAndOff.add")
	}
	return ValAndOff(makeValAndOff(x.Val(), x.Off()+int64(off)))
	}

	func (x ValAndOff) addOffset64(off int64) ValAndOff {
	if !x.canAdd(off) {
	panic("invalid ValAndOff.add")
	}
	return ValAndOff(makeValAndOff(x.Val(), x.Off()+off))
	}

	// int128 is a type that stores a 128-bit constant.
	// The only allowed constant right now is 0, so we can cheat quite a bit.
	type int128 int64

	type BoundsKind uint8

	const (
	BoundsIndex BoundsKind = iota // indexing operation, 0 <= idx < len failed
	BoundsIndexU // ... with unsigned idx
	BoundsSliceAlen // 2-arg slicing operation, 0 <= high <= len failed
	BoundsSliceAlenU // ... with unsigned high
	BoundsSliceAcap // 2-arg slicing operation, 0 <= high <= cap failed
	BoundsSliceAcapU // ... with unsigned high
	BoundsSliceB // 2-arg slicing operation, 0 <= low <= high failed
	BoundsSliceBU // ... with unsigned low
	BoundsSlice3Alen // 3-arg slicing operation, 0 <= max <= len failed
	BoundsSlice3AlenU // ... with unsigned max
	BoundsSlice3Acap // 3-arg slicing operation, 0 <= max <= cap failed
	BoundsSlice3AcapU // ... with unsigned max
	BoundsSlice3B // 3-arg slicing operation, 0 <= high <= max failed
	BoundsSlice3BU // ... with unsigned high
	BoundsSlice3C // 3-arg slicing operation, 0 <= low <= high failed
	BoundsSlice3CU // ... with unsigned low
	BoundsKindCount
	)

	// boundsAPI determines which register arguments a bounds check call should use. For an [a:b:c] slice, we do:
	// CMPQ c, cap
	// JA fail1
	// CMPQ b, c
	// JA fail2
	// CMPQ a, b
	// JA fail3
	//
	// fail1: CALL panicSlice3Acap (c, cap)
	// fail2: CALL panicSlice3B (b, c)
	// fail3: CALL panicSlice3C (a, b)
	//
	// When we register allocate that code, we want the same register to be used for
	// the first arg of panicSlice3Acap and the second arg to panicSlice3B. That way,
	// initializing that register once will satisfy both calls.
	// That desire ends up dividing the set of bounds check calls into 3 sets. This function
	// determines which set to use for a given panic call.
	// The first arg for set 0 should be the second arg for set 1.
	// The first arg for set 1 should be the second arg for set 2.
	func boundsABI(b int64) int {
	switch BoundsKind(b) {
	case BoundsSlice3Alen,
	BoundsSlice3AlenU,
	BoundsSlice3Acap,
	BoundsSlice3AcapU:
	return 0
	case BoundsSliceAlen,
	BoundsSliceAlenU,
	BoundsSliceAcap,
	BoundsSliceAcapU,
	BoundsSlice3B,
	BoundsSlice3BU:
	return 1
	case BoundsIndex,
	BoundsIndexU,
	BoundsSliceB,
	BoundsSliceBU,
	BoundsSlice3C,
	BoundsSlice3CU:
	return 2
	default:
	panic("bad BoundsKind")
	}
	}

	// arm64BitFileld is the GO type of ARM64BitField auxInt.
	// if x is an ARM64BitField, then width=x&0xff, lsb=(x>>8)&0xff, and
	// width+lsb<64 for 64-bit variant, width+lsb<32 for 32-bit variant.
	// the meaning of width and lsb are instruction-dependent.
	type arm64BitField int16