cmd/compile: rip out support for OpVarKill from ssa backend

Change-Id: I008479a7516d8379186ce630748e503d94d3b1e8
Reviewed-on: https://go-review.googlesource.com/c/go/+/419235
Reviewed-by: David Chase <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Keith Randall <[email protected]>

src/cmd/compile/internal/liveness/arg.go

@@ -249,7 +249,7 @@ func (lv *argLiveness) valueEffect(v *ssa.Value, live bitvec.BitVec) bool {
 func mayFault(v *ssa.Value) bool {
  switch v.Op {
  case ssa.OpLoadReg, ssa.OpStoreReg, ssa.OpCopy, ssa.OpPhi,
- ssa.OpVarDef, ssa.OpVarKill, ssa.OpVarLive, ssa.OpKeepAlive,
+ ssa.OpVarDef, ssa.OpVarLive, ssa.OpKeepAlive,
  ssa.OpSelect0, ssa.OpSelect1, ssa.OpSelectN, ssa.OpMakeResult,
  ssa.OpConvert, ssa.OpInlMark, ssa.OpGetG:
  return false

src/cmd/compile/internal/liveness/plive.go

@@ -80,15 +80,6 @@ import (
 // the liveness analysis work on single-word values as well, although
 // there are complications around interface values, slices, and strings,
 // all of which cannot be treated as individual words.
-//
-// OpVarKill is the opposite of OpVarDef: it marks a value as no longer needed,
-// even if its address has been taken. That is, an OpVarKill annotation asserts
-// that its argument is certainly dead, for use when the liveness analysis
-// would not otherwise be able to deduce that fact.
-
-// TODO: get rid of OpVarKill here. It's useful for stack frame allocation
-// so the compiler can allocate two temps to the same location. Here it's now
-// useless, since the implementation of stack objects.
 
 // blockEffects summarizes the liveness effects on an SSA block.
 type blockEffects struct {
@@ -269,7 +260,7 @@ func (lv *liveness) valueEffects(v *ssa.Value) (int32, liveEffect) {
  // OpVarFoo pseudo-ops. Ignore them to prevent "lost track of
  // variable" ICEs (issue 19632).
  switch v.Op {
- case ssa.OpVarDef, ssa.OpVarKill, ssa.OpVarLive, ssa.OpKeepAlive:
+ case ssa.OpVarDef, ssa.OpVarLive, ssa.OpKeepAlive:
  if !n.Used() {
  return -1, 0
  }
@@ -334,7 +325,7 @@ func affectedVar(v *ssa.Value) (*ir.Name, ssa.SymEffect) {
 
  case ssa.OpVarLive:
  return v.Aux.(*ir.Name), ssa.SymRead
- case ssa.OpVarDef, ssa.OpVarKill:
+ case ssa.OpVarDef:
  return v.Aux.(*ir.Name), ssa.SymWrite
  case ssa.OpKeepAlive:
  n, _ := ssa.AutoVar(v.Args[0])

src/cmd/compile/internal/ssa/deadstore.go

@@ -39,7 +39,7 @@ func dse(f *Func) {
  for _, a := range v.Args {
  if a.Block == b && a.Type.IsMemory() {
  storeUse.add(a.ID)
- if v.Op != OpStore && v.Op != OpZero && v.Op != OpVarDef && v.Op != OpVarKill {
+ if v.Op != OpStore && v.Op != OpZero && v.Op != OpVarDef {
  // CALL, DUFFCOPY, etc. are both
  // reads and writes.
  loadUse.add(a.ID)
@@ -156,7 +156,7 @@ func elimDeadAutosGeneric(f *Func) {
  changed = true
  }
  return
- case OpVarDef, OpVarKill:
+ case OpVarDef:
  // v should be eliminated if we eliminate the auto.
  n, ok := v.Aux.(*ir.Name)
  if !ok || n.Class != ir.PAUTO {

src/cmd/compile/internal/ssa/debug.go

@@ -613,7 +613,7 @@ func BuildFuncDebug(ctxt *obj.Link, f *Func, loggingLevel int, stackOffset func(
  // This would probably be better as an output from stackframe.
  for _, b := range f.Blocks {
  for _, v := range b.Values {
- if v.Op == OpVarDef || v.Op == OpVarKill {
+ if v.Op == OpVarDef {
  n := v.Aux.(*ir.Name)
  if ir.IsSynthetic(n) {
  continue
@@ -1080,7 +1080,7 @@ func (state *debugState) processValue(v *Value, vSlots []SlotID, vReg *Register)
  }
 
  switch {
- case v.Op == OpVarDef, v.Op == OpVarKill:
+ case v.Op == OpVarDef:
  n := v.Aux.(*ir.Name)
  if ir.IsSynthetic(n) {
  break

src/cmd/compile/internal/ssa/gen/genericOps.go

@@ -528,7 +528,6 @@ var genericOps = []opData{
  {name: "Unknown"},
 
  {name: "VarDef", argLength: 1, aux: "Sym", typ: "Mem", symEffect: "None", zeroWidth: true}, // aux is a *gc.Node of a variable that is about to be initialized. arg0=mem, returns mem
- {name: "VarKill", argLength: 1, aux: "Sym", symEffect: "None"}, // aux is a *gc.Node of a variable that is known to be dead. arg0=mem, returns mem
  // TODO: what's the difference between VarLive and KeepAlive?
  {name: "VarLive", argLength: 1, aux: "Sym", symEffect: "Read", zeroWidth: true}, // aux is a *gc.Node of a variable that must be kept live. arg0=mem, returns mem
  {name: "KeepAlive", argLength: 2, typ: "Mem", zeroWidth: true}, // arg[0] is a value that must be kept alive until this mark. arg[1]=mem, returns mem

src/cmd/compile/internal/ssa/lower.go

@@ -21,7 +21,7 @@ func checkLower(f *Func) {
  continue // lowered
  }
  switch v.Op {
- case OpSP, OpSB, OpInitMem, OpArg, OpArgIntReg, OpArgFloatReg, OpPhi, OpVarDef, OpVarKill, OpVarLive, OpKeepAlive, OpSelect0, OpSelect1, OpSelectN, OpConvert, OpInlMark:
+ case OpSP, OpSB, OpInitMem, OpArg, OpArgIntReg, OpArgFloatReg, OpPhi, OpVarDef, OpVarLive, OpKeepAlive, OpSelect0, OpSelect1, OpSelectN, OpConvert, OpInlMark:
  continue // ok not to lower
  case OpMakeResult:
  if b.Controls[0] == v {

src/cmd/compile/internal/ssa/nilcheck.go

@@ -236,7 +236,7 @@ func nilcheckelim2(f *Func) {
  continue
  }
  if v.Type.IsMemory() || v.Type.IsTuple() && v.Type.FieldType(1).IsMemory() {
- if v.Op == OpVarKill || v.Op == OpVarLive || (v.Op == OpVarDef && !v.Aux.(*ir.Name).Type().HasPointers()) {
+ if v.Op == OpVarLive || (v.Op == OpVarDef && !v.Aux.(*ir.Name).Type().HasPointers()) {
  // These ops don't really change memory.
  continue
  // Note: OpVarDef requires that the defined variable not have pointers.

src/cmd/compile/internal/ssa/numberlines.go

@@ -62,7 +62,7 @@ func nextGoodStatementIndex(v *Value, i int, b *Block) int {
 // statement boundary.
 func notStmtBoundary(op Op) bool {
  switch op {
- case OpCopy, OpPhi, OpVarKill, OpVarDef, OpVarLive, OpUnknown, OpFwdRef, OpArg, OpArgIntReg, OpArgFloatReg:
+ case OpCopy, OpPhi, OpVarDef, OpVarLive, OpUnknown, OpFwdRef, OpArg, OpArgIntReg, OpArgFloatReg:
  return true
  }
  return false

src/cmd/compile/internal/ssa/value.go

@@ -520,7 +520,7 @@ func (v *Value) LackingPos() bool {
  // The exact definition of LackingPos is somewhat heuristically defined and may change
  // in the future, for example if some of these operations are generated more carefully
  // with respect to their source position.
- return v.Op == OpVarDef || v.Op == OpVarKill || v.Op == OpVarLive || v.Op == OpPhi ||
+ return v.Op == OpVarDef || v.Op == OpVarLive || v.Op == OpPhi ||
  (v.Op == OpFwdRef || v.Op == OpCopy) && v.Type == types.TypeMem
 }
 

src/cmd/compile/internal/ssa/writebarrier.go

@@ -163,7 +163,7 @@ func writebarrier(f *Func) {
  last = w
  end = i + 1
  }
- case OpVarDef, OpVarLive, OpVarKill:
+ case OpVarDef, OpVarLive:
  continue
  default:
  if last == nil {
@@ -279,7 +279,7 @@ func writebarrier(f *Func) {
  fn = typedmemclr
  typ = reflectdata.TypeLinksym(w.Aux.(*types.Type))
  nWBops--
- case OpVarDef, OpVarLive, OpVarKill:
+ case OpVarDef, OpVarLive:
  }
 
  // then block: emit write barrier call
@@ -301,7 +301,7 @@ func writebarrier(f *Func) {
  }
  // Note that we set up a writebarrier function call.
  f.fe.SetWBPos(pos)
- case OpVarDef, OpVarLive, OpVarKill:
+ case OpVarDef, OpVarLive:
  memThen = bThen.NewValue1A(pos, w.Op, types.TypeMem, w.Aux, memThen)
  }
 
@@ -315,7 +315,7 @@ func writebarrier(f *Func) {
  case OpZeroWB:
  memElse = bElse.NewValue2I(pos, OpZero, types.TypeMem, w.AuxInt, ptr, memElse)
  memElse.Aux = w.Aux
- case OpVarDef, OpVarLive, OpVarKill:
+ case OpVarDef, OpVarLive:
  memElse = bElse.NewValue1A(pos, w.Op, types.TypeMem, w.Aux, memElse)
  }
  }

src/cmd/compile/internal/ssagen/ssa.go

@@ -1470,9 +1470,6 @@ func (s *state) stmt(n ir.Node) {
  s.Fatalf("dottype of non-load")
  }
  mem := s.mem()
- if mem.Op == ssa.OpVarKill {
- mem = mem.Args[0]
- }
  if res.Args[1] != mem {
  s.Fatalf("memory no longer live from 2-result dottype load")
  }
@@ -6947,7 +6944,7 @@ func genssa(f *ssa.Func, pp *objw.Progs) {
  case ssa.OpGetG:
  // nothing to do when there's a g register,
  // and checkLower complains if there's not
- case ssa.OpVarDef, ssa.OpVarLive, ssa.OpKeepAlive, ssa.OpVarKill:
+ case ssa.OpVarDef, ssa.OpVarLive, ssa.OpKeepAlive:
  // nothing to do; already used by liveness
  case ssa.OpPhi:
  CheckLoweredPhi(v)