$ valgrind perl -e'my $x; $x = \$x; undef $x if $ARGV[0]' 1
==21363== Memcheck, a memory error detector
==21363== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==21363== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==21363== Command: perl -emy\ $x;\ $x\ =\ \\$x;\ undef\ $x\ if\ $ARGV[0] 1
==21363== 
==21363== Warning: bad signal number 0 in sigaction()
==21363== 
==21363== HEAP SUMMARY:
==21363==     in use at exit: 80,794 bytes in 609 blocks
==21363==   total heap usage: 786 allocs, 177 frees, 93,378 bytes allocated
==21363== 
==21363== LEAK SUMMARY:
==21363==    definitely lost: 0 bytes in 0 blocks
==21363==    indirectly lost: 0 bytes in 0 blocks
==21363==      possibly lost: 14,538 bytes in 354 blocks
==21363==    still reachable: 66,256 bytes in 255 blocks
==21363==         suppressed: 0 bytes in 0 blocks
==21363== Rerun with --leak-check=full to see details of leaked memory
==21363== 
==21363== For counts of detected and suppressed errors, rerun with: -v
==21363== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 22 from 7)

$ valgrind perl -e'my $x; $x = \$x; undef $x if $ARGV[0]' 0
==21366== Memcheck, a memory error detector
==21366== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==21366== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==21366== Command: perl -emy\ $x;\ $x\ =\ \\$x;\ undef\ $x\ if\ $ARGV[0] 0
==21366== 
==21366== Warning: bad signal number 0 in sigaction()
==21366== 
==21366== HEAP SUMMARY:
==21366==     in use at exit: 80,794 bytes in 609 blocks
==21366==   total heap usage: 786 allocs, 177 frees, 93,378 bytes allocated
==21366== 
==21366== LEAK SUMMARY:
==21366==    definitely lost: 0 bytes in 0 blocks
==21366==    indirectly lost: 0 bytes in 0 blocks
==21366==      possibly lost: 14,538 bytes in 354 blocks
==21366==    still reachable: 66,256 bytes in 255 blocks
==21366==         suppressed: 0 bytes in 0 blocks
==21366== Rerun with --leak-check=full to see details of leaked memory
==21366== 
==21366== For counts of detected and suppressed errors, rerun with: -v
==21366== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 22 from 7)