[dev.regabi] cmd/compile: disallow taking address of SSA'd values

Adds some extra validation that the frontend is setting flags like
Addrtaken correctly.

Change-Id: Iffde83e32ba1c4c917ab8cb3fe410a4f623cf635
Reviewed-on: https://go-review.googlesource.com/c/go/+/286434
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -434,6 +434,7 @@ func buildssa(fn *ir.Func, worker int) *ssa.Func {
 		// bitmask showing which of the open-coded defers in this function
 		// have been activated.
 		deferBitsTemp := typecheck.TempAt(src.NoXPos, s.curfn, types.Types[types.TUINT8])
+		deferBitsTemp.SetAddrtaken(true)
 		s.deferBitsTemp = deferBitsTemp
 		// For this value, AuxInt is initialized to zero by default
 		startDeferBits := s.entryNewValue0(ssa.OpConst8, types.Types[types.TUINT8])
@@ -5086,6 +5087,10 @@ func (s *state) addr(n ir.Node) *ssa.Value {
 		defer s.popLine()
 	}
 
+	if s.canSSA(n) {
+		s.Fatalf("addr of canSSA expression: %+v", n)
+	}
+
 	t := types.NewPtr(n.Type())
 	linksymOffset := func(lsym *obj.LSym, offset int64) *ssa.Value {
 		v := s.entryNewValue1A(ssa.OpAddr, t, lsym, s.sb)