function.h (struct function): Add flag all_throwers_are_sibcalls.

2002-08-24  Stuart Hastings  <stuart@apple.com>

        * function.h (struct function): Add flag
        all_throwers_are_sibcalls.
        * except.c (set_nothrow_function_flags): Replaces
        nothrow_function_p. Set new flag.
        * except.h (set_nothrow_function_flags): Replaces
        nothrow_function_p.
        * dwarf2out.c (struct dw_fde_struct): Add flag
        all_throwers_are_sibcalls.
        (output_call_frame_info): Test it.
        (dwarf2out_begin_prologue) Propagate it from cfun to
        dw_fde_struct.
        * toplev.c (rest_of_compilation): Update calls to
        nothrow_function_p.

From-SVN: r56561

gcc/ChangeLog

@@ -1,3 +1,19 @@
+2002-08-24  Stuart Hastings  <stuart@apple.com>
+
+	* function.h (struct function): Add flag
+	all_throwers_are_sibcalls.
+	* except.c (set_nothrow_function_flags): Replaces
+	nothrow_function_p. Set new flag.
+	* except.h (set_nothrow_function_flags): Replaces
+	nothrow_function_p.
+	* dwarf2out.c (struct dw_fde_struct): Add flag
+	all_throwers_are_sibcalls.
+	(output_call_frame_info): Test it.
+	(dwarf2out_begin_prologue) Propagate it from cfun to
+	dw_fde_struct.
+	* toplev.c (rest_of_compilation): Update calls to
+	nothrow_function_p.
+
 2002-08-23  Zack Weinberg  <zack@codesourcery.com>
 
 	* ggc-page.c (compute_inverse): Short circuit calculation for

gcc/dwarf2out.c

@@ -203,6 +203,7 @@ typedef struct dw_fde_struct
   const char *dw_fde_end;
   dw_cfi_ref dw_fde_cfi;
   unsigned funcdef_number;
+  unsigned all_throwers_are_sibcalls : 1;
   unsigned nothrow : 1;
   unsigned uses_eh_lsda : 1;
 }
@@ -1952,8 +1953,9 @@ output_call_frame_info (for_eh)
       fde = &fde_table[i];
 
       /* Don't emit EH unwind info for leaf functions that don't need it.  */
-      if (!flag_asynchronous_unwind_tables && for_eh && fde->nothrow
-	  && !  fde->uses_eh_lsda)
+      if (!flag_asynchronous_unwind_tables && for_eh
+	  && (fde->nothrow || fde->all_throwers_are_sibcalls)
+	  && !fde->uses_eh_lsda)
 	continue;
 
       ASM_OUTPUT_INTERNAL_LABEL (asm_out_file, FDE_LABEL, for_eh + i * 2);
@@ -2115,6 +2117,7 @@ dwarf2out_begin_prologue (line, file)
   fde->funcdef_number = current_function_funcdef_no;
   fde->nothrow = current_function_nothrow;
   fde->uses_eh_lsda = cfun->uses_eh_lsda;
+  fde->all_throwers_are_sibcalls = cfun->all_throwers_are_sibcalls;
 
   args_size = old_args_size = 0;
 

gcc/except.c

@@ -2893,25 +2893,50 @@ can_throw_external (insn)
   return true;
 }
 
-/* True if nothing in this function can throw outside this function.  */
+/* Set current_function_nothrow and cfun->all_throwers_are_sibcalls.  */
 
-bool
-nothrow_function_p ()
+void
+set_nothrow_function_flags ()
 {
   rtx insn;
+  
+  current_function_nothrow = 1;
+
+  /* Assume cfun->all_throwers_are_sibcalls until we encounter
+     something that can throw an exception.  We specifically exempt
+     CALL_INSNs that are SIBLING_CALL_P, as these are really jumps,
+     and can't throw.  Most CALL_INSNs are not SIBLING_CALL_P, so this
+     is optimistic.  */
+
+  cfun->all_throwers_are_sibcalls = 1;
 
   if (! flag_exceptions)
-    return true;
-
+    return;
+  
   for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
     if (can_throw_external (insn))
-      return false;
+      {
+	current_function_nothrow = 0;
+
+	if (GET_CODE (insn) != CALL_INSN || !SIBLING_CALL_P (insn))
+	  {
+	    cfun->all_throwers_are_sibcalls = 0;
+	    return;
+	  }
+      }
+
   for (insn = current_function_epilogue_delay_list; insn;
        insn = XEXP (insn, 1))
-    if (can_throw_external (XEXP (insn, 0)))
-      return false;
+    if (can_throw_external (insn))
+      {
+	current_function_nothrow = 0;
 
-  return true;
+	if (GET_CODE (insn) != CALL_INSN || !SIBLING_CALL_P (insn))
+	  {
+	    cfun->all_throwers_are_sibcalls = 0;
+	    return;
+	  }
+      }
 }
 
 

gcc/except.h

@@ -91,8 +91,8 @@ extern void for_each_eh_label			PARAMS ((void (*) (rtx)));
 extern bool can_throw_internal			PARAMS ((rtx));
 extern bool can_throw_external			PARAMS ((rtx));
 
-/* Return nonzero if nothing in this function can throw.  */
-extern bool nothrow_function_p			PARAMS ((void));
+/* Set current_function_nothrow and cfun->all_throwers_are_sibcalls.  */
+extern void set_nothrow_function_flags		PARAMS ((void));
 
 /* After initial rtl generation, call back to finish generating
    exception support code.  */

gcc/function.h

@@ -437,6 +437,13 @@ struct function GTY(())
      we should try to cut corners where we can.  */
   unsigned int is_thunk : 1;
 
+  /* This bit is used by the exception handling logic.  It is set if all
+     calls (if any) are sibling calls.  Such functions do not have to
+     have EH tables generated, as they cannot throw.  A call to such a
+     function, however, should be treated as throwing if any of its callees
+     can throw. */
+  unsigned int all_throwers_are_sibcalls : 1;
+ 
   /* Nonzero if instrumentation calls for function entry and exit should be
      generated.  */
   unsigned int instrument_entry_exit : 1;

gcc/toplev.c

@@ -2506,7 +2506,7 @@ rest_of_compilation (decl)
 	      free_bb_for_insn ();
 	    }
 
-	  current_function_nothrow = nothrow_function_p ();
+	  set_nothrow_function_flags ();
 	  if (current_function_nothrow)
 	    /* Now we know that this can't throw; set the flag for the benefit
 	       of other functions later in this translation unit.  */
@@ -3528,7 +3528,7 @@ rest_of_compilation (decl)
   shorten_branches (get_insns ());
   timevar_pop (TV_SHORTEN_BRANCH);
 
-  current_function_nothrow = nothrow_function_p ();
+  set_nothrow_function_flags ();
   if (current_function_nothrow)
     /* Now we know that this can't throw; set the flag for the benefit
        of other functions later in this translation unit.  */