add padrange op

This single op can, in some circumstances, replace the sequence of a
pushmark followed by one or more padsv/padav/padhv ops, and possibly
a trailing 'list' op, but only where the targs of the pad ops form
a continuous range.

This is generally more efficient, but is particularly so in the case
of void-context my declarations, such as:

    my ($a,@b);

Formerly this would be executed as the following set of ops:

    pushmark  pushes a new mark
    padsv[$a] pushes $a, does a SAVEt_CLEARSV
    padav[@b] pushes all the flattened elements (i.e. none) of @a,
              does a SAVEt_CLEARSV
    list      pops the mark, and pops all stack elements except the last
    nextstate pops the remaining stack element

It's now:

    padrange[$a..@b] does two SAVEt_CLEARSV's
    nextstate        nothing needing doing to the stack

Note that in the case above, this commit changes user-visible behaviour in
pathological cases; in particular, it has always been possible to modify a
lexical var *before* the my is executed, using goto or closure tricks.
So in principle someone could tie an array, then could notice that FETCH
is no longer being called, e.g.

    f();
    my ($s, @a); # this no longer triggers two FETCHES
    sub f {
	tie @a, ...;
	push @a, 1,2;
    }

But I think we can live with that.

Note also that having a padrange operator will allow us shortly to have
a corresponding SAVEt_CLEARPADRANGE save type, that will replace multiple
individual SAVEt_CLEARSV's.

1 files changed, 23 insertions, 0 deletions

diff --git a/pp_hot.c b/pp_hot.c
index 212fe5f9e7..e5ea2cc8bc 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -306,6 +306,29 @@ PP(pp_concat)
   }
 }
 
+/* ($lex1,@lex2,...)   or my ($lex1,@lex2,...)  */
+
+PP(pp_padrange)
+{
+    dVAR; dSP;
+    PADOFFSET base = PL_op->op_targ;
+    int count = (int)(PL_op->op_private) & OPpPADRANGE_COUNTMASK;
+    int i;
+    /* note, this is only skipped for compile-time-known void cxt */
+    if ((PL_op->op_flags & OPf_WANT) != OPf_WANT_VOID) {
+        EXTEND(SP, count);
+        PUSHMARK(SP);
+        for (i = 0; i <count; i++)
+            *++SP = PAD_SV(base+i);
+    }
+    if (PL_op->op_private & OPpLVAL_INTRO) {
+        for (i = 0; i <count; i++)
+            SAVECLEARSV(PAD_SVl(base+i));
+    }
+    RETURN;
+}
+
+
 PP(pp_padsv)
 {
     dVAR; dSP; dTARGET;