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, 4 insertions, 3 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 34542c27f5..3414365b61 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -223,13 +223,14 @@ PP(pp_cond_expr)
 PP(pp_unstack)
 {
     dVAR;
-    I32 oldsave;
     PERL_ASYNC_CHECK();
     TAINT_NOT;		/* Each statement is presumed innocent */
     PL_stack_sp = PL_stack_base + cxstack[cxstack_ix].blk_oldsp;
     FREETMPS;
-    oldsave = PL_scopestack[PL_scopestack_ix - 1];
-    LEAVE_SCOPE(oldsave);
+    if (!(PL_op->op_flags & OPf_SPECIAL)) {
+	I32 oldsave = PL_scopestack[PL_scopestack_ix - 1];
+	LEAVE_SCOPE(oldsave);
+    }
     return NORMAL;
 }