eliminate the argarray field from the CX struct

At the end of a normal sub call there are often 3 AVs of interest
associated with @_; these are:

    cx->blk_sub.savearray  the caller's @_
    GvAV(PL_defgv)         the current sub's current @_
    cx->blk_sub.argarray   the current sub's original @_

Note that those last two can differ: if for example the sub does

    local *_ = [];

Each sub's arg array is created and stored in pad slot 0 at the time
the sub is created. When a sub is called, pp_entersub() does

    cx->blk_sub.argarray = PL_curpad[0]

The argarray field is used in two main places:

* at subroutine exit, to clear/abandon the sub's original @_;
* in pp_caller, to set @DB::args to the caller(n)'s args.

In the first case, the last few commits have arranged things so that at
that point, PL_curpad always points to the current pad of the sub being
exited from. So we can just use PL_curpad[0] rather than
cx->blk_sub.argarray.

In the second case (which is not performance critical), we can just use
    cx->blk_sub.cv
and
    cx->blk_sub.olddepth+1
to find the pad of that call frame's CV.

So we can eliminate the argarray field. This saves a write during
a sub call, and potentially reduces the size of the context struct.

It also makes the code marginally less confusing: there are now 3 arrays
pointed to from 3 places, rather than 3 arrays pointed to from 4 places.

The asserts added in the previous commit confirmed that using argarray
is the same as using PL_curpad[0]; They also confirmed that the current
PL_curpad matches the current CV at the current depth. Those latter
asserts are kept for now.

1 files changed, 0 insertions, 1 deletions

diff --git a/pp_sort.c b/pp_sort.c
index 73f520d7d4..1e48042a9f 100644
--- a/pp_sort.c
+++ b/pp_sort.c
@@ -1688,7 +1688,6 @@ PP(pp_sort)
 
 			cx->blk_sub.savearray = GvAV(PL_defgv);
 			GvAV(PL_defgv) = MUTABLE_AV(SvREFCNT_inc_simple(av));
-			cx->blk_sub.argarray = av;
 		    }
 
 		}