From: Nicholas Clark <nick@ccl4.org>
Date: Thu, 15 Jul 2004 12:47:50 +0000 (+0000)
Subject: for (reverse @foo) now iterates in reverse in place.
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=e682d7b7fae5a50c5afb147f913a4e88d7261606;p=p5sagit%2Fp5-mst-13.2.git

for (reverse @foo) now iterates in reverse in place.

p4raw-id: //depot/perl@23115
---

diff --git a/op.c b/op.c
index e9ea2e5..ea714eb 100644
--- a/op.c
+++ b/op.c
@@ -6719,7 +6719,7 @@ Perl_peep(pTHX_ register OP *o)
 	}
 
 	case OP_REVERSE: {
-	    OP *ourmark, *theirmark, *ourlast, *iter, *expushmark;
+	    OP *ourmark, *theirmark, *ourlast, *iter, *expushmark, *rv2av;
 	    OP *gvop = NULL;
 	    LISTOP *enter, *exlist;
 	    o->op_opt = 1;
@@ -6786,6 +6786,15 @@ Perl_peep(pTHX_ register OP *o)
 	    if (!ourlast || ourlast->op_next != o)
 		break;
 
+	    rv2av = ourmark->op_sibling;
+	    if (rv2av && rv2av->op_type == OP_RV2AV && rv2av->op_sibling == 0
+		&& rv2av->op_flags == (OPf_WANT_LIST | OPf_KIDS)
+		&& enter->op_flags == (OPf_WANT_LIST | OPf_KIDS)) {
+		/* We're just reversing a single array.  */
+		rv2av->op_flags = OPf_WANT_SCALAR | OPf_KIDS | OPf_REF;
+		enter->op_flags |= OPf_STACKED;
+	    }
+
 	    /* We don't have control over who points to theirmark, so sacrifice
 	       ours.  */
 	    theirmark->op_next = ourmark->op_next;
diff --git a/pod/perltodo.pod b/pod/perltodo.pod
index 1560956..0c3e8d6 100644
--- a/pod/perltodo.pod
+++ b/pod/perltodo.pod
@@ -179,15 +179,6 @@ Clean these up. Move them to mathom.c, and don't compile for blead?
 The old perltodo notes "This has been done in places, but needs a thorough
 code review. Also fchdir is available in some platforms."
 
-=head2 foreach reverse
-
-The old perltodo notes that we could optimise foreach to iterate in reverse.
-(instead of making a reversed copy on the stack)
-It seems that cx->blk_loop.itermax could be hijacked to act as a go up/go
-down flag, with cx->blk_loop.iterix primed in pp_enteriter for the go down
-case (ie reverse). However, it looks slightly tricky identifying the shape of
-foreach reverse in the optree in Perl_peep.
-
 =head1 Tests
 
 =head2 Make Schwern poorer
diff --git a/pp_ctl.c b/pp_ctl.c
index 1107ad9..0c1067a 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -1811,7 +1811,7 @@ PP(pp_enteriter)
 	    }
 	}
 	else if (PL_op->op_private & OPpITER_REVERSED) {
-	    cx->blk_loop.itermax = 0;
+	    cx->blk_loop.itermax = -1;
 	    cx->blk_loop.iterix = AvFILL(cx->blk_loop.iterary);
 
 	}