Change 33709 by [EMAIL PROTECTED] on 2008/04/17 20:17:14
Add "eliminate incorrect line numbers in warnings" to perltodo, and
a pair of TODO tests for the desired behaviour.
Affected files ...
... //depot/perl/pod/perltodo.pod#222 edit
... //depot/perl/t/lib/warnings/9uninit#23 edit
Differences ...
==== //depot/perl/pod/perltodo.pod#222 (text) ====
Index: perl/pod/perltodo.pod
--- perl/pod/perltodo.pod#221~33708~ 2008-04-17 08:15:48.000000000 -0700
+++ perl/pod/perltodo.pod 2008-04-17 13:17:14.000000000 -0700
@@ -919,6 +919,61 @@
cause their slabs to be freed, which would eliminate possible memory wastage if
the previous suggestion is implemented, and we swap slabs more frequently.
+=head2 eliminate incorrect line numbers in warnings
+
+This code
+
+ use warnings;
+ my $undef;
+
+ if ($undef == 3) {
+ } elsif ($undef == 0) {
+ }
+
+produces this output
+
+ Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
+ Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
+
+Clearly the line of the second warning is misreported - it should be line 5.
+
+The problem arises because there is no nextstate op between the execution of
+the C<if> and the C<elsif>, hence C<PL_curcop> still reports that the currently
+executing line is line 4. The solution might be to inject (somehow) more
+nextstate ops, one for each C<elsif>.
+
+The problem is more general than C<elsif> (although the C<elsif> case is the
+most common and the most confusing). Ideally this code
+
+ use warnings;
+ my $undef;
+
+ my $a = $undef + 1;
+ my $b
+ = $undef
+ + 1;
+
+would produce this output
+
+ Use of uninitialized value $undef in addition (+) at wrong.pl line 4.
+ Use of uninitialized value $undef in addition (+) at wrong.pl line 7.
+
+(rather than lines 4 and 5), but this would seem to require every OP to carry
+(at least) line number information.
+
+What might work is to have an optional line number in memory just before the
+BASEOP structure, with a flag bit in the op to say whether it's present.
+Initially during compile every OP would carry its line number. Then add a late
+pass to the optimiser (potentially combined with L</repack the optree>) which
+looks at the two ops on every edge of the graph of the execution path. If
+the line number changes, flags the destination OP with this information.
+Once all paths are traced, replace every op with the flag with a
+nextstate-light op (that just updates C<PL_curcop>), which in turn then passes
+control on to the true op. All ops would then be replaced by variants that
+do not store the line number. (Which, logically, why it would work best in
+conjunction with L</repack the optree>, as that is already copying/reallocating
+all the OPs)
+
=head2 optimize tail-calls
Tail-calls present an opportunity for broadly applicable optimization;
==== //depot/perl/t/lib/warnings/9uninit#23 (text) ====
Index: perl/t/lib/warnings/9uninit
--- perl/t/lib/warnings/9uninit#22~33557~ 2008-03-25 02:17:28.000000000
-0700
+++ perl/t/lib/warnings/9uninit 2008-04-17 13:17:14.000000000 -0700
@@ -1321,3 +1321,26 @@
exit $m1;
EXPECT
Use of uninitialized value $m1 in exit at - line 4.
+########
+# TODO long standing bug - PL_curcop is not updated before the elsif
+use warnings 'uninitialized';
+my $undef;
+
+if ($undef == 3) {
+} elsif ($undef == 0) {
+}
+EXPECT
+Use of uninitialized value $undef in numeric eq (==) at - line 4.
+Use of uninitialized value $undef in numeric eq (==) at - line 5.
+########
+# TODO long standing bug - more general variant of the above problem
+use warnings;
+my $undef;
+
+my $a = $undef + 1;
+my $b
+ = $undef
+ + 1;
+EXPECT
+Use of uninitialized value $undef in addition (+) at - line 4.
+Use of uninitialized value $undef in addition (+) at - line 7.
End of Patch.
