Optimize away the assignment in the constructs C<my $s = undef>,

C<my @a = ()>, C<my %h = ()>.

p4raw-id: //depot/perl@22520

diff --git a/op.c b/op.c
index b4d1ffc..344130c 100644 (file)
--- a/op.c
+++ b/op.c
@@ -3126,6 +3126,14 @@ Perl_newASSIGNOP(pTHX_ I32 flags, OP *left, I32 optype, OP *right)
            op_free(right);
            return Nullop;
        }
+       /* optimise C<my @x = ()> to C<my @x>, and likewise for hashes */
+       if ((left->op_type == OP_PADAV || left->op_type == OP_PADHV)
+               && right->op_type == OP_STUB
+               && (left->op_private & OPpLVAL_INTRO))
+       {
+           op_free(right);
+           return left;
+       }
        curop = list(force_list(left));
        o = newBINOP(OP_AASSIGN, flags, list(force_list(right)), curop);
        o->op_private = (U8)(0 | (flags >> 8));
@@ -5593,6 +5601,19 @@ Perl_ck_sassign(pTHX_ OP *o)
            return kid;
        }
     }
+    /* optimise C<my $x = undef> to C<my $x> */
+    if (kid->op_type == OP_UNDEF) {
+       OP *kkid = kid->op_sibling;
+       if (kkid && kkid->op_type == OP_PADSV
+               && (kkid->op_private & OPpLVAL_INTRO))
+       {
+           cLISTOPo->op_first = NULL;
+           kid->op_sibling = NULL;
+           op_free(o);
+           op_free(kid);
+           return kkid;
+       }
+    }
     return o;
 }