refactor and regularise label/statement grammar

Refactoring of the grammar around statements.  New production <barestmt>
encompasses a statement without label.  It includes all statement types,
including declarations, with no unnecessary intermediate non-terminals.
It generates an op tree for the statement's content, with no leading
state op.  The <fullstmt> production has just one rule, consisting of
optional label followed by <barestmt>.  It puts a state op on the front
of the statement's content ops.

To support the regular statement op structure, the op sequence for for(;;)
loops no longer has a second state op between the initialisation and
the loop.  Instead, the unstack op type is slightly adapted to achieve
the stack clearing without a state op.

The newFOROP() constructor function no longer generates a state op,
that now being the job of the <fullstmt> production.  Consequently it
no longer takes a parameter stating what label is to go in the state op.
This brings it in line with the other op constructors.

1 files changed, 8 insertions, 0 deletions

diff --git a/pp_ctl.c b/pp_ctl.c
index 9eebf43c65..b3c7ba21ce 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -2783,6 +2783,14 @@ PP(pp_goto)
 				    enterops, enterops + GOTO_DEPTH);
 		if (retop)
 		    break;
+		if (gotoprobe->op_sibling &&
+			gotoprobe->op_sibling->op_type == OP_UNSTACK &&
+			gotoprobe->op_sibling->op_sibling) {
+		    retop = dofindlabel(gotoprobe->op_sibling->op_sibling,
+					label, enterops, enterops + GOTO_DEPTH);
+		    if (retop)
+			break;
+		}
 	    }
 	    PL_lastgotoprobe = gotoprobe;
 	}