cmd/compile: rip out support for OVARKILL from compiler frontend

Change-Id: I2c5b1064084bade68aaa065cf74dca6886fb752f
Reviewed-on: https://go-review.googlesource.com/c/go/+/419236
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Run-TryBot: Keith Randall <[email protected]>
Reviewed-by: David Chase <[email protected]>

src/cmd/compile/internal/ir/expr.go

@@ -734,7 +734,7 @@ func (n *UnaryExpr) SetOp(op Op) {
  case OBITNOT, ONEG, ONOT, OPLUS, ORECV,
  OALIGNOF, OCAP, OCLOSE, OIMAG, OLEN, ONEW,
  OOFFSETOF, OPANIC, OREAL, OSIZEOF,
- OCHECKNIL, OCFUNC, OIDATA, OITAB, OSPTR, OVARDEF, OVARKILL, OVARLIVE:
+ OCHECKNIL, OCFUNC, OIDATA, OITAB, OSPTR, OVARDEF, OVARLIVE:
  n.op = op
  }
 }

src/cmd/compile/internal/ir/node.go

@@ -289,7 +289,6 @@ const (
  OCFUNC // reference to c function pointer (not go func value)
  OCHECKNIL // emit code to ensure pointer/interface not nil
  OVARDEF // variable is about to be fully initialized
- OVARKILL // variable is dead
  OVARLIVE // variable is alive
  ORESULT // result of a function call; Xoffset is stack offset
  OINLMARK // start of an inlined body, with file/line of caller. Xoffset is an index into the inline tree.

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

@@ -1384,8 +1384,8 @@ func (s *state) stmtList(l ir.Nodes) {
 
 // stmt converts the statement n to SSA and adds it to s.
 func (s *state) stmt(n ir.Node) {
- if !(n.Op() == ir.OVARKILL || n.Op() == ir.OVARLIVE || n.Op() == ir.OVARDEF) {
- // OVARKILL, OVARLIVE, and OVARDEF are invisible to the programmer, so we don't use their line numbers to avoid confusion in debugging.
+ if !(n.Op() == ir.OVARLIVE || n.Op() == ir.OVARDEF) {
+ // OVARLIVE and OVARDEF are invisible to the programmer, so we don't use their line numbers to avoid confusion in debugging.
  s.pushLine(n.Pos())
  defer s.popLine()
  }

src/cmd/compile/internal/typecheck/typecheck.go

@@ -359,7 +359,7 @@ func typecheck(n ir.Node, top int) (res ir.Node) {
  case ir.OAPPEND:
  // Must be used (and not BinaryExpr/UnaryExpr).
  isStmt = false
- case ir.OCLOSE, ir.ODELETE, ir.OPANIC, ir.OPRINT, ir.OPRINTN, ir.OVARKILL, ir.OVARLIVE:
+ case ir.OCLOSE, ir.ODELETE, ir.OPANIC, ir.OPRINT, ir.OPRINTN, ir.OVARLIVE:
  // Must not be used.
  isExpr = false
  isStmt = true
@@ -750,7 +750,6 @@ func typecheck1(n ir.Node, top int) ir.Node {
  ir.ODCL,
  ir.OGOTO,
  ir.OFALL,
- ir.OVARKILL,
  ir.OVARLIVE:
  return n
 

src/cmd/compile/internal/walk/order.go

@@ -597,7 +597,7 @@ func (o *orderState) stmt(n ir.Node) {
  default:
  base.Fatalf("order.stmt %v", n.Op())
 
- case ir.OVARKILL, ir.OVARLIVE, ir.OINLMARK:
+ case ir.OVARLIVE, ir.OINLMARK:
  o.out = append(o.out, n)
 
  case ir.OAS:

src/cmd/compile/internal/walk/stmt.go

@@ -91,7 +91,6 @@ func walkStmt(n ir.Node) ir.Node {
  ir.ODCLTYPE,
  ir.OCHECKNIL,
  ir.OVARDEF,
- ir.OVARKILL,
  ir.OVARLIVE:
  return n
 

src/cmd/compile/internal/walk/switch.go

@@ -372,19 +372,10 @@ func allCaseExprsAreSideEffectFree(sw *ir.SwitchStmt) bool {
 
 // endsInFallthrough reports whether stmts ends with a "fallthrough" statement.
 func endsInFallthrough(stmts []ir.Node) (bool, src.XPos) {
- // Search backwards for the index of the fallthrough
- // statement. Do not assume it'll be in the last
- // position, since in some cases (e.g. when the statement
- // list contains autotmp_ variables), one or more OVARKILL
- // nodes will be at the end of the list.
-
- i := len(stmts) - 1
- for i >= 0 && stmts[i].Op() == ir.OVARKILL {
- i--
- }
- if i < 0 {
+ if len(stmts) == 0 {
  return false, src.NoXPos
  }
+ i := len(stmts) - 1
  return stmts[i].Op() == ir.OFALL, stmts[i].Pos()
 }