Add --enable-sharing-preserving configure flag

4 files changed, 20 insertions, 4 deletions

diff --git a/configure.in b/configure.in
index e8c8680e19..51728a847e 100644
--- a/configure.in
+++ b/configure.in
@@ -278,6 +278,10 @@ AC_ARG_ENABLE(builtin-zlib,
 AS_HELP_STRING([--enable-builtin-zlib],
                [force use of our own built-in zlib]))
 
+AC_ARG_ENABLE(sharing-preserving,
+AS_HELP_STRING([--enable-sharing-preserving],
+               [enable copying of terms without destroying sharing]))
+
 dnl This functionality has been lost along the way... :(
 dnl It could perhaps be nice to reintroduce some day; therefore,
 dnl it is not removed just commented out.
diff --git a/erts/configure.in b/erts/configure.in
index 2419925c33..9ad1588b6c 100644
--- a/erts/configure.in
+++ b/erts/configure.in
@@ -788,6 +788,18 @@ esac
 	
 AC_SUBST(LIBCARBON)
 
+dnl Check if we should/can build a sharing-preserving emulator
+
+AC_MSG_CHECKING(if we are building a sharing-preserving emulator)
+if test "$enable_sharing_preserving" = "yes"; then
+        AC_DEFINE(SHCOPY, [1],
+		  [Define if building a sharing-preserving emulator])
+	AC_MSG_RESULT([yes])
+else
+	AC_MSG_RESULT([no])
+fi
+
+
 dnl some tests below will call this if we haven't already - and autoconf
 dnl can't handle those tests being done conditionally at runtime
 AC_PROG_CPP
diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 1eb106a551..82c2aa4b9e 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -130,6 +130,9 @@ static char erts_system_version[] = ("Erlang/OTP " ERLANG_OTP_RELEASE
 #ifdef USE_SYSTEMTAP
 				     " [systemtap]"
 #endif
+#ifdef SHCOPY
+				     " [sharing-preserving]"
+#endif
 				     "\n");
 
 #define ASIZE(a) (sizeof(a)/sizeof(a[0]))
diff --git a/erts/emulator/beam/global.h b/erts/emulator/beam/global.h
index 303b9ee51b..3c59df5f41 100644
--- a/erts/emulator/beam/global.h
+++ b/erts/emulator/beam/global.h
@@ -1038,12 +1038,9 @@ void erl_error(char*, va_list);
 
 /* This controls whether sharing-preserving copy is used by Erlang */
 
+#ifdef SHCOPY
 #define SHCOPY_SEND
 #define SHCOPY_SPAWN
-
-#if defined(SHCOPY_SEND) \
- || defined(SHCOPY_SPAWN)
-#define SHCOPY
 /* Use this if you want sharing-preserving copy to be initially disabled */
 #undef SHCOPY_DISABLE
 #endif