Restore functional DONT_USE_BUILTIN_SETJMP support

[Eric Botcazou <ebotcazou@adacore.com>]

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DONT_USE_BUILTIN_SETJMP is an old configuration macro that instructs the 
compiler to use the usual setjmp/longjmp routines instead of their built-in 
variants to implement SJLJ exceptions.  It's less efficient but, sometimes, 
the setjmp/longjmp routines have specific features that cannot be easily 
implemented by the built-in.  Only IA-64 and Aarch64 define it.

The support is currently broken at compile time (because of a broken CFG) and 
at link time (an unresolved symbol).  The attached small patch restores it.

Bootstrapped & tested on Aarch64/Linux with --enable-sjlj-exceptions, applied 
on the mainline as obvious.


2017-10-07  Eric Botcazou  <ebotcazou@adacore.com>

	* builtins.def (BUILT_IN_SETJMP): Declare as library builtin instead
	of GCC builtin if DONT_USE_BUILTIN_SETJMP is defined.
	* except.c (sjlj_emit_function_enter): If DONT_USE_BUILTIN_SETJMP is
	defined, force the creation of a new block for a dispatch label.

-- 
Eric Botcazou

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Index: builtins.def
===================================================================
--- builtins.def	(revision 253506)
+++ builtins.def	(working copy)
@@ -890,7 +890,11 @@ DEF_LIB_BUILTIN        (BUILT_IN_REALLOC
 DEF_GCC_BUILTIN        (BUILT_IN_RETURN, "return", BT_FN_VOID_PTR, ATTR_NORETURN_NOTHROW_LEAF_LIST)
 DEF_GCC_BUILTIN        (BUILT_IN_RETURN_ADDRESS, "return_address", BT_FN_PTR_UINT, ATTR_LEAF_LIST)
 DEF_GCC_BUILTIN        (BUILT_IN_SAVEREGS, "saveregs", BT_FN_PTR_VAR, ATTR_NULL)
+#ifdef DONT_USE_BUILTIN_SETJMP
+DEF_LIB_BUILTIN        (BUILT_IN_SETJMP, "setjmp", BT_FN_INT_PTR, ATTR_RT_NOTHROW_LEAF_LIST)
+#else
 DEF_GCC_BUILTIN        (BUILT_IN_SETJMP, "setjmp", BT_FN_INT_PTR, ATTR_RT_NOTHROW_LEAF_LIST)
+#endif
 DEF_EXT_LIB_BUILTIN    (BUILT_IN_STRFMON, "strfmon", BT_FN_SSIZE_STRING_SIZE_CONST_STRING_VAR, ATTR_FORMAT_STRFMON_NOTHROW_3_4)
 DEF_LIB_BUILTIN        (BUILT_IN_STRFTIME, "strftime", BT_FN_SIZE_STRING_SIZE_CONST_STRING_CONST_TM_PTR, ATTR_FORMAT_STRFTIME_NOTHROW_3_0)
 DEF_GCC_BUILTIN        (BUILT_IN_TRAP, "trap", BT_FN_VOID, ATTR_NORETURN_NOTHROW_LEAF_COLD_LIST)
Index: except.c
===================================================================
--- except.c	(revision 253506)
+++ except.c	(working copy)
@@ -1209,6 +1209,28 @@ sjlj_emit_function_enter (rtx_code_label
 	  fn_begin_outside_block = false;
       }
 
+#ifdef DONT_USE_BUILTIN_SETJMP
+  if (dispatch_label)
+    {
+      /* The sequence contains a branch in the middle so we need to force
+	 the creation of a new basic block by means of BB_SUPERBLOCK.  */
+      if (fn_begin_outside_block)
+	{
+	  basic_block bb
+	    = split_edge (single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
+	  if (JUMP_P (BB_END (bb)))
+	    emit_insn_before (seq, BB_END (bb));
+	  else
+	    emit_insn_after (seq, BB_END (bb));
+	}
+      else
+	emit_insn_after (seq, fn_begin);
+
+      single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun))->flags |= BB_SUPERBLOCK;
+      return;
+    }
+#endif
+
   if (fn_begin_outside_block)
     insert_insn_on_edge (seq, single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
   else