Re: constant function inlining

(this is the same change as commit f0893e72a8aa916a77953ff2f1847494d1527fb8, but as applied)

2 files changed, 21 insertions, 0 deletions

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index a9bdb9b1d3..fb0a2d76c0 100644
--- 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 6bd3fe8d84..bd3eb18154 100644
--- a/pod/perlsub.pod
+++ b/pod/perlsub.pod
@@ -754,6 +754,21 @@ 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.  
 
+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
 
 Many builtin functions may be overridden, though this should be tried