Re: constant function inlining

On Tue, 7 Jan 1997 18:21:28 +0000, Tim Bunce <Tim.Bunce@ig.co.uk> said:
>
> A few words about redefining [constant] functions would be worthwhile.

Right, patch attached.

p5p-msgid: <pzk9pp1b95.fsf@eeyore.ibcinc.com>

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index a9bdb9b..fb0a2d7 100644 (file)
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -812,6 +812,12 @@ to 01411.  Octal constants are introduced with a leading 0 in Perl, as in C.
 (W) You tried to do a connect on a closed socket.  Did you forget to check
 the return value of your socket() call?  See L<perlfunc/connect>.
 
+=item Constant subroutine %s redefined
+
+(S) You redefined a subroutine which had previously been eligible for
+inlining.  See L<perlsub/"Constant Functions"> for commentary and
+workarounds.
+
 =item Corrupt malloc ptr 0x%lx at 0x%lx
 
 (P) The malloc package that comes with Perl had an internal failure.

diff --git a/pod/perlsub.pod b/pod/perlsub.pod
index 6bd3fe8..fa14a7f 100644 (file)
--- a/pod/perlsub.pod
+++ b/pod/perlsub.pod
@@ -752,7 +752,22 @@ in @foo.  And the split() gets called in a scalar context and
 starts scribbling on your @_ parameter list.
 
 This is all very powerful, of course, and should be used only in moderation
-to make the world a better place.  
+to make the world a better place.
+
+If you redefine a subroutine which was eligible for inlining you'll get
+a mandatory warning.  (You can use this warning to tell whether or not a
+particular subroutine is considered constant.)  The warning is
+considered severe enough not to be optional because previously compiled
+invocations of the function will still be using the old value of the
+function.  If you need to be able to redefine the subroutine you need to
+ensure that it isn't inlined, either by dropping the C<()> prototype
+(which changes the calling semantics, so beware) or by thwarting the
+inlining mechanism in some other way, such as
+
+    my $dummy;
+    sub not_inlined () {
+       $dummy || 23
+    }
 
 =head2 Overriding Builtin Functions