Avoid redundant copies in string evals

Perl_lex_start copies the string passed to it unconditionally.
Sometimes pp_entereval makes a copy before passing the string
to lex_start.  So in those cases we can pass a flag to avoid a
redundant copy.

1 files changed, 5 insertions, 8 deletions

diff --git a/toke.c b/toke.c
index 6e88c8a25c..1431cc377d 100644
--- a/toke.c
+++ b/toke.c
@@ -726,16 +726,13 @@ Perl_lex_start(pTHX_ SV *line, PerlIO *rsfp, U32 flags)
 
     if (line) {
 	s = SvPV_const(line, len);
-    } else {
-	len = 0;
-    }
-
-    if (!len) {
-	parser->linestr = newSVpvs("\n;");
-    } else {
-	parser->linestr = newSVpvn_flags(s, len, SvUTF8(line));
+	parser->linestr = flags & LEX_START_COPIED
+			    ? SvREFCNT_inc_simple_NN(line)
+			    : newSVpvn_flags(s, len, SvUTF8(line));
 	if (s[len-1] != ';')
 	    sv_catpvs(parser->linestr, "\n;");
+    } else {
+	parser->linestr = newSVpvs("\n;");
     }
     parser->oldoldbufptr =
 	parser->oldbufptr =