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, 5 insertions, 0 deletions

diff --git a/opcode.h b/opcode.h
index 02769ba347..540dc0ba97 100644
--- a/opcode.h
+++ b/opcode.h
@@ -524,6 +524,7 @@ EXTCONST char* const PL_op_name[] = {
 	"padcv",
 	"introcv",
 	"clonecv",
+	"padrange",
 	"freed",
 };
 #endif
@@ -908,6 +909,7 @@ EXTCONST char* const PL_op_desc[] = {
 	"private subroutine",
 	"private subroutine",
 	"private subroutine",
+	"list of private variables",
 	"freed op",
 };
 #endif
@@ -1306,6 +1308,7 @@ EXT Perl_ppaddr_t PL_ppaddr[] /* or perlvars.h */
 	Perl_pp_padcv,
 	Perl_pp_introcv,
 	Perl_pp_clonecv,
+	Perl_pp_padrange,
 }
 #endif
 #ifdef PERL_PPADDR_INITED
@@ -1700,6 +1703,7 @@ EXT Perl_check_t PL_check[] /* or perlvars.h */
 	Perl_ck_null,		/* padcv */
 	Perl_ck_null,		/* introcv */
 	Perl_ck_null,		/* clonecv */
+	Perl_ck_null,		/* padrange */
 }
 #endif
 #ifdef PERL_CHECK_INITED
@@ -2088,6 +2092,7 @@ EXTCONST U32 PL_opargs[] = {
 	0x00000040,	/* padcv */
 	0x00000040,	/* introcv */
 	0x00000040,	/* clonecv */
+	0x00000040,	/* padrange */
 };
 #endif