configure: Define NO_JUMP_TABLE if all we have is llvm-gcc

Commit dd24ca1cb76d attempts to fix the problem that LLVM-based
compilers (such as llvm-gcc-4.2 and clang) miscompiles beam_emu.c.
The idea was to force the use of gcc-4.2 if the default compiler
was LLVM-based.

Since that fix, Apple released Xcode 4.2 that does not include
any version of gcc, only llvm-gcc-4.2 and clang.

We could require gcc in order to be the system, but it would be
nice if Erlang/OTP could be built out-of-box on MacOS X, albeit
with reduced performance.

Therefore, make sure that we set NO_JUMP_TABLE (use a switch
statement instead of computed gotos in beam_emu.c) if no compiler
that correctly handles computed gotos can be found.

We know that clang based on the upcoming LLVM 3.0 will work, but older
LLVM-based compilers will not, so we can test the version of clang.
llvm-gcc has been discontinued in LLVM 3.0, so if the compiler is
LLVM-based but not clang, we can assume that it does not handles
computed gotos correctly.

1 files changed, 9 insertions, 2 deletions

diff --git a/erts/aclocal.m4 b/erts/aclocal.m4
index bd228a2d1f..ea5cc67fbe 100644
--- a/erts/aclocal.m4
+++ b/erts/aclocal.m4
@@ -125,8 +125,10 @@ AC_DEFUN(LM_FIND_EMU_CC,
 			ac_cv_prog_emu_cc,
 			[
 AC_TRY_COMPILE([],[
-#ifdef __llvm__
-#error "llvm is currently unable to compile beam_emu.c"
+#if defined(__clang_major__) && __clang_major__ >= 3
+    /* clang 3.x or later is fine */
+#elif defined(__llvm__)
+#error "this version of llvm is unable to correctly compile beam_emu.c"
 #endif
     __label__ lbl1;
     __label__ lbl2;
@@ -168,6 +170,11 @@ if test $ac_cv_prog_emu_cc != no; then
 	CFLAGS=""
 	CPPFLAGS=""
 	AC_TRY_COMPILE([],[
+#if defined(__clang_major__) && __clang_major__ >= 3
+    /* clang 3.x or later is fine */
+#elif defined(__llvm__)
+#error "this version of llvm is unable to correctly compile beam_emu.c"
+#endif
     	__label__ lbl1;
     	__label__ lbl2;
     	int x = magic();