[dev.regabi] cmd/compile: add ssa.Aux tag interface for Value.Aux

It's currently hard to automate refactorings around the Value.Aux
field, because we don't have any static typing information for it.
Adding a tag interface will make subsequent CLs easier and safer.

Passes buildall w/ toolstash -cmp.

Updates #42982.

Change-Id: I41ae8e411a66bda3195a0957b60c2fe8a8002893
Reviewed-on: https://go-review.googlesource.com/c/go/+/275756
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>

20 files changed, 79 insertions, 56 deletions

diff --git a/src/cmd/compile/fmtmap_test.go b/src/cmd/compile/fmtmap_test.go
index 756320285c..e62b9613e1 100644
--- a/src/cmd/compile/fmtmap_test.go
+++ b/src/cmd/compile/fmtmap_test.go
@@ -43,6 +43,9 @@ var knownFormats = map[string]string{
 	"cmd/compile/internal/ir.Nodes %+v":            "",
 	"cmd/compile/internal/ir.Nodes %.v":            "",
 	"cmd/compile/internal/ir.Op %+v":               "",
+	"cmd/compile/internal/ssa.Aux %#v":             "",
+	"cmd/compile/internal/ssa.Aux %q":              "",
+	"cmd/compile/internal/ssa.Aux %s":              "",
 	"cmd/compile/internal/ssa.BranchPrediction %d": "",
 	"cmd/compile/internal/ssa.ID %d":               "",
 	"cmd/compile/internal/ssa.LocalSlot %s":        "",
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index add50c35d7..95650328b1 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -772,7 +772,7 @@ func (s *state) newValue0(op ssa.Op, t *types.Type) *ssa.Value {
 }
 
 // newValue0A adds a new value with no arguments and an aux value to the current block.
-func (s *state) newValue0A(op ssa.Op, t *types.Type, aux interface{}) *ssa.Value {
+func (s *state) newValue0A(op ssa.Op, t *types.Type, aux ssa.Aux) *ssa.Value {
 	return s.curBlock.NewValue0A(s.peekPos(), op, t, aux)
 }
 
@@ -787,14 +787,14 @@ func (s *state) newValue1(op ssa.Op, t *types.Type, arg *ssa.Value) *ssa.Value {
 }
 
 // newValue1A adds a new value with one argument and an aux value to the current block.
-func (s *state) newValue1A(op ssa.Op, t *types.Type, aux interface{}, arg *ssa.Value) *ssa.Value {
+func (s *state) newValue1A(op ssa.Op, t *types.Type, aux ssa.Aux, arg *ssa.Value) *ssa.Value {
 	return s.curBlock.NewValue1A(s.peekPos(), op, t, aux, arg)
 }
 
 // newValue1Apos adds a new value with one argument and an aux value to the current block.
 // isStmt determines whether the created values may be a statement or not
 // (i.e., false means never, yes means maybe).
-func (s *state) newValue1Apos(op ssa.Op, t *types.Type, aux interface{}, arg *ssa.Value, isStmt bool) *ssa.Value {
+func (s *state) newValue1Apos(op ssa.Op, t *types.Type, aux ssa.Aux, arg *ssa.Value, isStmt bool) *ssa.Value {
 	if isStmt {
 		return s.curBlock.NewValue1A(s.peekPos(), op, t, aux, arg)
 	}
@@ -812,14 +812,14 @@ func (s *state) newValue2(op ssa.Op, t *types.Type, arg0, arg1 *ssa.Value) *ssa.
 }
 
 // newValue2A adds a new value with two arguments and an aux value to the current block.
-func (s *state) newValue2A(op ssa.Op, t *types.Type, aux interface{}, arg0, arg1 *ssa.Value) *ssa.Value {
+func (s *state) newValue2A(op ssa.Op, t *types.Type, aux ssa.Aux, arg0, arg1 *ssa.Value) *ssa.Value {
 	return s.curBlock.NewValue2A(s.peekPos(), op, t, aux, arg0, arg1)
 }
 
 // newValue2Apos adds a new value with two arguments and an aux value to the current block.
 // isStmt determines whether the created values may be a statement or not
 // (i.e., false means never, yes means maybe).
-func (s *state) newValue2Apos(op ssa.Op, t *types.Type, aux interface{}, arg0, arg1 *ssa.Value, isStmt bool) *ssa.Value {
+func (s *state) newValue2Apos(op ssa.Op, t *types.Type, aux ssa.Aux, arg0, arg1 *ssa.Value, isStmt bool) *ssa.Value {
 	if isStmt {
 		return s.curBlock.NewValue2A(s.peekPos(), op, t, aux, arg0, arg1)
 	}
@@ -842,14 +842,14 @@ func (s *state) newValue3I(op ssa.Op, t *types.Type, aux int64, arg0, arg1, arg2
 }
 
 // newValue3A adds a new value with three arguments and an aux value to the current block.
-func (s *state) newValue3A(op ssa.Op, t *types.Type, aux interface{}, arg0, arg1, arg2 *ssa.Value) *ssa.Value {
+func (s *state) newValue3A(op ssa.Op, t *types.Type, aux ssa.Aux, arg0, arg1, arg2 *ssa.Value) *ssa.Value {
 	return s.curBlock.NewValue3A(s.peekPos(), op, t, aux, arg0, arg1, arg2)
 }
 
 // newValue3Apos adds a new value with three arguments and an aux value to the current block.
 // isStmt determines whether the created values may be a statement or not
 // (i.e., false means never, yes means maybe).
-func (s *state) newValue3Apos(op ssa.Op, t *types.Type, aux interface{}, arg0, arg1, arg2 *ssa.Value, isStmt bool) *ssa.Value {
+func (s *state) newValue3Apos(op ssa.Op, t *types.Type, aux ssa.Aux, arg0, arg1, arg2 *ssa.Value, isStmt bool) *ssa.Value {
 	if isStmt {
 		return s.curBlock.NewValue3A(s.peekPos(), op, t, aux, arg0, arg1, arg2)
 	}
@@ -872,7 +872,7 @@ func (s *state) entryNewValue0(op ssa.Op, t *types.Type) *ssa.Value {
 }
 
 // entryNewValue0A adds a new value with no arguments and an aux value to the entry block.
-func (s *state) entryNewValue0A(op ssa.Op, t *types.Type, aux interface{}) *ssa.Value {
+func (s *state) entryNewValue0A(op ssa.Op, t *types.Type, aux ssa.Aux) *ssa.Value {
 	return s.f.Entry.NewValue0A(src.NoXPos, op, t, aux)
 }
 
@@ -887,7 +887,7 @@ func (s *state) entryNewValue1I(op ssa.Op, t *types.Type, auxint int64, arg *ssa
 }
 
 // entryNewValue1A adds a new value with one argument and an aux value to the entry block.
-func (s *state) entryNewValue1A(op ssa.Op, t *types.Type, aux interface{}, arg *ssa.Value) *ssa.Value {
+func (s *state) entryNewValue1A(op ssa.Op, t *types.Type, aux ssa.Aux, arg *ssa.Value) *ssa.Value {
 	return s.f.Entry.NewValue1A(src.NoXPos, op, t, aux, arg)
 }
 
@@ -897,7 +897,7 @@ func (s *state) entryNewValue2(op ssa.Op, t *types.Type, arg0, arg1 *ssa.Value)
 }
 
 // entryNewValue2A adds a new value with two arguments and an aux value to the entry block.
-func (s *state) entryNewValue2A(op ssa.Op, t *types.Type, aux interface{}, arg0, arg1 *ssa.Value) *ssa.Value {
+func (s *state) entryNewValue2A(op ssa.Op, t *types.Type, aux ssa.Aux, arg0, arg1 *ssa.Value) *ssa.Value {
 	return s.f.Entry.NewValue2A(src.NoXPos, op, t, aux, arg0, arg1)
 }
 
@@ -2060,7 +2060,7 @@ func (s *state) expr(n ir.Node) *ssa.Value {
 			if i == "" {
 				return s.constEmptyString(n.Type())
 			}
-			return s.entryNewValue0A(ssa.OpConstString, n.Type(), i)
+			return s.entryNewValue0A(ssa.OpConstString, n.Type(), ssa.StringToAux(i))
 		case constant.Bool:
 			return s.constBool(constant.BoolVal(u))
 		case constant.Float:
diff --git a/src/cmd/compile/internal/ir/mini.go b/src/cmd/compile/internal/ir/mini.go
index 612e7d62c3..edb3b197da 100644
--- a/src/cmd/compile/internal/ir/mini.go
+++ b/src/cmd/compile/internal/ir/mini.go
@@ -198,5 +198,6 @@ func (n *miniNode) MarkReadonly()             { panic(n.no("MarkReadonly")) }
 func (n *miniNode) TChanDir() types.ChanDir   { panic(n.no("TChanDir")) }
 func (n *miniNode) SetTChanDir(types.ChanDir) { panic(n.no("SetTChanDir")) }
 
-// TODO: Delete when CanBeAnSSASym is removed from Node itself.
+// TODO: Delete when these are removed from Node itself.
 func (*miniNode) CanBeAnSSASym() {}
+func (*miniNode) CanBeAnSSAAux() {}
diff --git a/src/cmd/compile/internal/ir/node.go b/src/cmd/compile/internal/ir/node.go
index ba7eaae1b9..b878b00546 100644
--- a/src/cmd/compile/internal/ir/node.go
+++ b/src/cmd/compile/internal/ir/node.go
@@ -113,6 +113,7 @@ type Node interface {
 	// Only for SSA and should be removed when SSA starts
 	// using a more specific type than Node.
 	CanBeAnSSASym()
+	CanBeAnSSAAux()
 }
 
 // Line returns n's position as a string. If n has been inlined,
diff --git a/src/cmd/compile/internal/ssa/block.go b/src/cmd/compile/internal/ssa/block.go
index 519ac214ca..937c757b21 100644
--- a/src/cmd/compile/internal/ssa/block.go
+++ b/src/cmd/compile/internal/ssa/block.go
@@ -52,7 +52,7 @@ type Block struct {
 	Controls [2]*Value
 
 	// Auxiliary info for the block. Its value depends on the Kind.
-	Aux    interface{}
+	Aux    Aux
 	AuxInt int64
 
 	// The unordered set of Values that define the operation of this block.
diff --git a/src/cmd/compile/internal/ssa/check.go b/src/cmd/compile/internal/ssa/check.go
index 5f5dfc328a..4d57eef556 100644
--- a/src/cmd/compile/internal/ssa/check.go
+++ b/src/cmd/compile/internal/ssa/check.go
@@ -161,7 +161,7 @@ func checkFunc(f *Func) {
 					f.Fatalf("value %v has an AuxInt that encodes a NaN", v)
 				}
 			case auxString:
-				if _, ok := v.Aux.(string); !ok {
+				if _, ok := v.Aux.(stringAux); !ok {
 					f.Fatalf("value %v has Aux type %T, want string", v, v.Aux)
 				}
 				canHaveAux = true
diff --git a/src/cmd/compile/internal/ssa/cse.go b/src/cmd/compile/internal/ssa/cse.go
index 3b4f2be37e..f78527410c 100644
--- a/src/cmd/compile/internal/ssa/cse.go
+++ b/src/cmd/compile/internal/ssa/cse.go
@@ -275,7 +275,7 @@ func lt2Cmp(isLt bool) types.Cmp {
 	return types.CMPgt
 }
 
-type auxmap map[interface{}]int32
+type auxmap map[Aux]int32
 
 func cmpVal(v, w *Value, auxIDs auxmap) types.Cmp {
 	// Try to order these comparison by cost (cheaper first)
diff --git a/src/cmd/compile/internal/ssa/cse_test.go b/src/cmd/compile/internal/ssa/cse_test.go
index 9e76645f54..8052016f3a 100644
--- a/src/cmd/compile/internal/ssa/cse_test.go
+++ b/src/cmd/compile/internal/ssa/cse_test.go
@@ -14,6 +14,8 @@ type tstAux struct {
 	s string
 }
 
+func (*tstAux) CanBeAnSSAAux() {}
+
 // This tests for a bug found when partitioning, but not sorting by the Aux value.
 func TestCSEAuxPartitionBug(t *testing.T) {
 	c := testConfig(t)
diff --git a/src/cmd/compile/internal/ssa/debug.go b/src/cmd/compile/internal/ssa/debug.go
index 0d660361b1..44e91270fa 100644
--- a/src/cmd/compile/internal/ssa/debug.go
+++ b/src/cmd/compile/internal/ssa/debug.go
@@ -143,13 +143,13 @@ func (loc VarLoc) absent() bool {
 var BlockStart = &Value{
 	ID:  -10000,
 	Op:  OpInvalid,
-	Aux: "BlockStart",
+	Aux: StringToAux("BlockStart"),
 }
 
 var BlockEnd = &Value{
 	ID:  -20000,
 	Op:  OpInvalid,
-	Aux: "BlockEnd",
+	Aux: StringToAux("BlockEnd"),
 }
 
 // RegisterSet is a bitmap of registers, indexed by Register.num.
diff --git a/src/cmd/compile/internal/ssa/func.go b/src/cmd/compile/internal/ssa/func.go
index e6f899a2c7..e6c4798a78 100644
--- a/src/cmd/compile/internal/ssa/func.go
+++ b/src/cmd/compile/internal/ssa/func.go
@@ -377,13 +377,7 @@ func (b *Block) NewValue0I(pos src.XPos, op Op, t *types.Type, auxint int64) *Va
 }
 
 // NewValue returns a new value in the block with no arguments and an aux value.
-func (b *Block) NewValue0A(pos src.XPos, op Op, t *types.Type, aux interface{}) *Value {
-	if _, ok := aux.(int64); ok {
-		// Disallow int64 aux values. They should be in the auxint field instead.
-		// Maybe we want to allow this at some point, but for now we disallow it
-		// to prevent errors like using NewValue1A instead of NewValue1I.
-		b.Fatalf("aux field has int64 type op=%s type=%s aux=%v", op, t, aux)
-	}
+func (b *Block) NewValue0A(pos src.XPos, op Op, t *types.Type, aux Aux) *Value {
 	v := b.Func.newValue(op, t, b, pos)
 	v.AuxInt = 0
 	v.Aux = aux
@@ -392,7 +386,7 @@ func (b *Block) NewValue0A(pos src.XPos, op Op, t *types.Type, aux interface{})
 }
 
 // NewValue returns a new value in the block with no arguments and both an auxint and aux values.
-func (b *Block) NewValue0IA(pos src.XPos, op Op, t *types.Type, auxint int64, aux interface{}) *Value {
+func (b *Block) NewValue0IA(pos src.XPos, op Op, t *types.Type, auxint int64, aux Aux) *Value {
 	v := b.Func.newValue(op, t, b, pos)
 	v.AuxInt = auxint
 	v.Aux = aux
@@ -421,7 +415,7 @@ func (b *Block) NewValue1I(pos src.XPos, op Op, t *types.Type, auxint int64, arg
 }
 
 // NewValue1A returns a new value in the block with one argument and an aux value.
-func (b *Block) NewValue1A(pos src.XPos, op Op, t *types.Type, aux interface{}, arg *Value) *Value {
+func (b *Block) NewValue1A(pos src.XPos, op Op, t *types.Type, aux Aux, arg *Value) *Value {
 	v := b.Func.newValue(op, t, b, pos)
 	v.AuxInt = 0
 	v.Aux = aux
@@ -432,7 +426,7 @@ func (b *Block) NewValue1A(pos src.XPos, op Op, t *types.Type, aux interface{},
 }
 
 // NewValue1IA returns a new value in the block with one argument and both an auxint and aux values.
-func (b *Block) NewValue1IA(pos src.XPos, op Op, t *types.Type, auxint int64, aux interface{}, arg *Value) *Value {
+func (b *Block) NewValue1IA(pos src.XPos, op Op, t *types.Type, auxint int64, aux Aux, arg *Value) *Value {
 	v := b.Func.newValue(op, t, b, pos)
 	v.AuxInt = auxint
 	v.Aux = aux
@@ -455,7 +449,7 @@ func (b *Block) NewValue2(pos src.XPos, op Op, t *types.Type, arg0, arg1 *Value)
 }
 
 // NewValue2A returns a new value in the block with two arguments and one aux values.
-func (b *Block) NewValue2A(pos src.XPos, op Op, t *types.Type, aux interface{}, arg0, arg1 *Value) *Value {
+func (b *Block) NewValue2A(pos src.XPos, op Op, t *types.Type, aux Aux, arg0, arg1 *Value) *Value {
 	v := b.Func.newValue(op, t, b, pos)
 	v.AuxInt = 0
 	v.Aux = aux
@@ -480,7 +474,7 @@ func (b *Block) NewValue2I(pos src.XPos, op Op, t *types.Type, auxint int64, arg
 }
 
 // NewValue2IA returns a new value in the block with two arguments and both an auxint and aux values.
-func (b *Block) NewValue2IA(pos src.XPos, op Op, t *types.Type, auxint int64, aux interface{}, arg0, arg1 *Value) *Value {
+func (b *Block) NewValue2IA(pos src.XPos, op Op, t *types.Type, auxint int64, aux Aux, arg0, arg1 *Value) *Value {
 	v := b.Func.newValue(op, t, b, pos)
 	v.AuxInt = auxint
 	v.Aux = aux
@@ -521,7 +515,7 @@ func (b *Block) NewValue3I(pos src.XPos, op Op, t *types.Type, auxint int64, arg
 }
 
 // NewValue3A returns a new value in the block with three argument and an aux value.
-func (b *Block) NewValue3A(pos src.XPos, op Op, t *types.Type, aux interface{}, arg0, arg1, arg2 *Value) *Value {
+func (b *Block) NewValue3A(pos src.XPos, op Op, t *types.Type, aux Aux, arg0, arg1, arg2 *Value) *Value {
 	v := b.Func.newValue(op, t, b, pos)
 	v.AuxInt = 0
 	v.Aux = aux
@@ -633,7 +627,7 @@ func (f *Func) ConstNil(t *types.Type) *Value {
 }
 func (f *Func) ConstEmptyString(t *types.Type) *Value {
 	v := f.constVal(OpConstString, t, constEmptyStringMagic, false)
-	v.Aux = ""
+	v.Aux = StringToAux("")
 	return v
 }
 func (f *Func) ConstOffPtrSP(t *types.Type, c int64, sp *Value) *Value {
diff --git a/src/cmd/compile/internal/ssa/func_test.go b/src/cmd/compile/internal/ssa/func_test.go
index 568c6436f5..276c444b9a 100644
--- a/src/cmd/compile/internal/ssa/func_test.go
+++ b/src/cmd/compile/internal/ssa/func_test.go
@@ -232,7 +232,7 @@ func Bloc(name string, entries ...interface{}) bloc {
 }
 
 // Valu defines a value in a block.
-func Valu(name string, op Op, t *types.Type, auxint int64, aux interface{}, args ...string) valu {
+func Valu(name string, op Op, t *types.Type, auxint int64, aux Aux, args ...string) valu {
 	return valu{name, op, t, auxint, aux, args}
 }
 
@@ -277,7 +277,7 @@ type valu struct {
 	op     Op
 	t      *types.Type
 	auxint int64
-	aux    interface{}
+	aux    Aux
 	args   []string
 }
 
@@ -402,12 +402,12 @@ func TestEquiv(t *testing.T) {
 			cfg.Fun("entry",
 				Bloc("entry",
 					Valu("mem", OpInitMem, types.TypeMem, 0, nil),
-					Valu("a", OpConst64, cfg.config.Types.Int64, 0, 14),
+					Valu("a", OpConstString, cfg.config.Types.String, 0, StringToAux("foo")),
 					Exit("mem"))),
 			cfg.Fun("entry",
 				Bloc("entry",
 					Valu("mem", OpInitMem, types.TypeMem, 0, nil),
-					Valu("a", OpConst64, cfg.config.Types.Int64, 0, 26),
+					Valu("a", OpConstString, cfg.config.Types.String, 0, StringToAux("bar")),
 					Exit("mem"))),
 		},
 		// value args different
diff --git a/src/cmd/compile/internal/ssa/nilcheck_test.go b/src/cmd/compile/internal/ssa/nilcheck_test.go
index 16d94614d8..2e32afe2a6 100644
--- a/src/cmd/compile/internal/ssa/nilcheck_test.go
+++ b/src/cmd/compile/internal/ssa/nilcheck_test.go
@@ -212,7 +212,7 @@ func TestNilcheckPhi(t *testing.T) {
 			Valu("mem", OpInitMem, types.TypeMem, 0, nil),
 			Valu("sb", OpSB, c.config.Types.Uintptr, 0, nil),
 			Valu("sp", OpSP, c.config.Types.Uintptr, 0, nil),
-			Valu("baddr", OpLocalAddr, c.config.Types.Bool, 0, "b", "sp", "mem"),
+			Valu("baddr", OpLocalAddr, c.config.Types.Bool, 0, StringToAux("b"), "sp", "mem"),
 			Valu("bool1", OpLoad, c.config.Types.Bool, 0, nil, "baddr", "mem"),
 			If("bool1", "b1", "b2")),
 		Bloc("b1",
diff --git a/src/cmd/compile/internal/ssa/op.go b/src/cmd/compile/internal/ssa/op.go
index 6f029a421e..97726a6f95 100644
--- a/src/cmd/compile/internal/ssa/op.go
+++ b/src/cmd/compile/internal/ssa/op.go
@@ -197,6 +197,8 @@ func ClosureAuxCall(args []Param, results []Param) *AuxCall {
 	return &AuxCall{Fn: nil, args: args, results: results}
 }
 
+func (*AuxCall) CanBeAnSSAAux() {}
+
 const (
 	auxNone         auxType = iota
 	auxBool                 // auxInt is 0/1 for false/true
@@ -248,6 +250,7 @@ const (
 type Sym interface {
 	String() string
 	CanBeAnSSASym()
+	CanBeAnSSAAux()
 }
 
 // A ValAndOff is used by the several opcodes. It holds
diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index 24efd38fb7..9abfe0938b 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -678,43 +678,53 @@ func opToAuxInt(o Op) int64 {
 	return int64(o)
 }
 
-func auxToString(i interface{}) string {
-	return i.(string)
+// Aux is an interface to hold miscellaneous data in Blocks and Values.
+type Aux interface {
+	CanBeAnSSAAux()
 }
-func auxToSym(i interface{}) Sym {
+
+// stringAux wraps string values for use in Aux.
+type stringAux string
+
+func (stringAux) CanBeAnSSAAux() {}
+
+func auxToString(i Aux) string {
+	return string(i.(stringAux))
+}
+func auxToSym(i Aux) Sym {
 	// TODO: kind of a hack - allows nil interface through
 	s, _ := i.(Sym)
 	return s
 }
-func auxToType(i interface{}) *types.Type {
+func auxToType(i Aux) *types.Type {
 	return i.(*types.Type)
 }
-func auxToCall(i interface{}) *AuxCall {
+func auxToCall(i Aux) *AuxCall {
 	return i.(*AuxCall)
 }
-func auxToS390xCCMask(i interface{}) s390x.CCMask {
+func auxToS390xCCMask(i Aux) s390x.CCMask {
 	return i.(s390x.CCMask)
 }
-func auxToS390xRotateParams(i interface{}) s390x.RotateParams {
+func auxToS390xRotateParams(i Aux) s390x.RotateParams {
 	return i.(s390x.RotateParams)
 }
 
-func stringToAux(s string) interface{} {
-	return s
+func StringToAux(s string) Aux {
+	return stringAux(s)
 }
-func symToAux(s Sym) interface{} {
+func symToAux(s Sym) Aux {
 	return s
 }
-func callToAux(s *AuxCall) interface{} {
+func callToAux(s *AuxCall) Aux {
 	return s
 }
-func typeToAux(t *types.Type) interface{} {
+func typeToAux(t *types.Type) Aux {
 	return t
 }
-func s390xCCMaskToAux(c s390x.CCMask) interface{} {
+func s390xCCMaskToAux(c s390x.CCMask) Aux {
 	return c
 }
-func s390xRotateParamsToAux(r s390x.RotateParams) interface{} {
+func s390xRotateParamsToAux(r s390x.RotateParams) Aux {
 	return r
 }
 
@@ -725,7 +735,7 @@ func uaddOvf(a, b int64) bool {
 
 // de-virtualize an InterCall
 // 'sym' is the symbol for the itab
-func devirt(v *Value, aux interface{}, sym Sym, offset int64) *AuxCall {
+func devirt(v *Value, aux Aux, sym Sym, offset int64) *AuxCall {
 	f := v.Block.Func
 	n, ok := sym.(*obj.LSym)
 	if !ok {
@@ -748,7 +758,7 @@ func devirt(v *Value, aux interface{}, sym Sym, offset int64) *AuxCall {
 
 // de-virtualize an InterLECall
 // 'sym' is the symbol for the itab
-func devirtLESym(v *Value, aux interface{}, sym Sym, offset int64) *obj.LSym {
+func devirtLESym(v *Value, aux Aux, sym Sym, offset int64) *obj.LSym {
 	n, ok := sym.(*obj.LSym)
 	if !ok {
 		return nil
diff --git a/src/cmd/compile/internal/ssa/value.go b/src/cmd/compile/internal/ssa/value.go
index edc43aaae7..993c5a580f 100644
--- a/src/cmd/compile/internal/ssa/value.go
+++ b/src/cmd/compile/internal/ssa/value.go
@@ -36,7 +36,7 @@ type Value struct {
 	// Users of AuxInt which interpret AuxInt as unsigned (e.g. shifts) must be careful.
 	// Use Value.AuxUnsigned to get the zero-extended value of AuxInt.
 	AuxInt int64
-	Aux    interface{}
+	Aux    Aux
 
 	// Arguments of this value
 	Args []*Value
@@ -492,3 +492,6 @@ func (v *Value) removeable() bool {
 	}
 	return true
 }
+
+// TODO(mdempsky): Shouldn't be necessary; see discussion at golang.org/cl/275756
+func (*Value) CanBeAnSSAAux() {}
diff --git a/src/cmd/compile/internal/ssa/zcse.go b/src/cmd/compile/internal/ssa/zcse.go
index ec38b7d1ba..e08272c345 100644
--- a/src/cmd/compile/internal/ssa/zcse.go
+++ b/src/cmd/compile/internal/ssa/zcse.go
@@ -57,7 +57,7 @@ func zcse(f *Func) {
 type vkey struct {
 	op Op
 	ai int64       // aux int
-	ax interface{} // aux
+	ax Aux         // aux
 	t  *types.Type // type
 }
 
diff --git a/src/cmd/compile/internal/types/type.go b/src/cmd/compile/internal/types/type.go
index c5807af199..e968a799e3 100644
--- a/src/cmd/compile/internal/types/type.go
+++ b/src/cmd/compile/internal/types/type.go
@@ -164,6 +164,8 @@ type Type struct {
 	flags bitset8
 }
 
+func (*Type) CanBeAnSSAAux() {}
+
 const (
 	typeNotInHeap  = 1 << iota // type cannot be heap allocated
 	typeBroke                  // broken type definition
diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go
index 8c8ff587ff..eaebfaf4b6 100644
--- a/src/cmd/internal/obj/link.go
+++ b/src/cmd/internal/obj/link.go
@@ -723,8 +723,8 @@ func (s *LSym) String() string {
 }
 
 // The compiler needs *LSym to be assignable to cmd/compile/internal/ssa.Sym.
-func (s *LSym) CanBeAnSSASym() {
-}
+func (*LSym) CanBeAnSSASym() {}
+func (*LSym) CanBeAnSSAAux() {}
 
 type Pcln struct {
 	// Aux symbols for pcln
diff --git a/src/cmd/internal/obj/s390x/condition_code.go b/src/cmd/internal/obj/s390x/condition_code.go
index 764fc5bc6a..f498fd6f77 100644
--- a/src/cmd/internal/obj/s390x/condition_code.go
+++ b/src/cmd/internal/obj/s390x/condition_code.go
@@ -124,3 +124,5 @@ func (c CCMask) String() string {
 	// invalid
 	return fmt.Sprintf("Invalid (%#x)", c)
 }
+
+func (CCMask) CanBeAnSSAAux() {}
diff --git a/src/cmd/internal/obj/s390x/rotate.go b/src/cmd/internal/obj/s390x/rotate.go
index 7dbc45e648..c999880492 100644
--- a/src/cmd/internal/obj/s390x/rotate.go
+++ b/src/cmd/internal/obj/s390x/rotate.go
@@ -113,3 +113,5 @@ func (r RotateParams) OutMerge(mask uint64) *RotateParams {
 func (r RotateParams) InMerge(mask uint64) *RotateParams {
 	return r.OutMerge(bits.RotateLeft64(mask, int(r.Amount)))
 }
+
+func (RotateParams) CanBeAnSSAAux() {}