Allow to enable ivsalloc independently

INSTALL

@@ -79,6 +79,12 @@ any of the following arguments (not a definitive list) to 'configure':
 --enable-debug
     Enable assertions and validation code.  This incurs a substantial
     performance hit, but is very useful during application development.
+    Implies --enable-ivsalloc.
+
+--enable-ivsalloc
+    Enable validation code, which verifies that pointers reside within
+    jemalloc-owned chunks before dereferencing them. This incurs a substantial
+    performance hit.
 
 --disable-stats
     Disable statistics gathering functionality.  See the "opt.stats_print"

configure.ac

@@ -551,7 +551,7 @@ fi
 
 dnl Do not compile with debugging by default.
 AC_ARG_ENABLE([debug],
-  [AS_HELP_STRING([--enable-debug], [Build debugging code])],
+  [AS_HELP_STRING([--enable-debug], [Build debugging code (implies --enable-ivsalloc)])],
 [if test "x$enable_debug" = "xno" ; then
   enable_debug="0"
 else
@@ -562,10 +562,25 @@ fi
 )
 if test "x$enable_debug" = "x1" ; then
   AC_DEFINE([JEMALLOC_DEBUG], [ ])
-  AC_DEFINE([JEMALLOC_IVSALLOC], [ ])
+  enable_ivsalloc="1"
 fi
 AC_SUBST([enable_debug])
 
+dnl Do not validate pointers by default.
+AC_ARG_ENABLE([ivsalloc],
+  [AS_HELP_STRING([--enable-ivsalloc], [Validate pointers passed through the public API])],
+[if test "x$enable_ivsalloc" = "xno" ; then
+  enable_ivsalloc="0"
+else
+  enable_ivsalloc="1"
+fi
+],
+[enable_ivsalloc="0"]
+)
+if test "x$enable_ivsalloc" = "x1" ; then
+  AC_DEFINE([JEMALLOC_IVSALLOC], [ ])
+fi
+
 dnl Only optimize if not debugging.
 if test "x$enable_debug" = "x0" -a "x$no_CFLAGS" = "xyes" ; then
   dnl Make sure that an optimization flag was not specified in EXTRA_CFLAGS.