Optimise __SUB__ to a constant

If __SUB__ is not inside a closure, it can be optimised to a constant.
We can only do this in the peephole optimiser, as we cannot tell
whether PL_compcv will become a closure until we reach the end
of the sub.

The __SUB__ op cannot simply be replaced with a const op, as the par-
ent op is not readily available in the peephole optimiser and, hence,
we cannot change its pointer.

So we have to convert the runcv op itself into a const op.  So it
has to be the same size.  This commit makes it a PVOP, since newPVOP,
unlike newSVOP, allows a null pv.  To avoid adding workarounds to B
modules, I put an exception in newPVOP’s assertion, instead of chang-
ing the type in regen/opcodes.

But B::Deparse still had to be updated to avoid infinite recursion.

1 files changed, 1 insertions, 1 deletions

diff --git a/toke.c b/toke.c
index a9b5e498e9..e5da941510 100644
--- a/toke.c
+++ b/toke.c
@@ -7128,7 +7128,7 @@ Perl_yylex(pTHX)
 	}
 
 	case KEY___SUB__:
-	    FUN0(OP_RUNCV);
+	    FUN0OP(newPVOP(OP_RUNCV,0,NULL));
 
 	case KEY_AUTOLOAD:
 	case KEY_DESTROY: