gcse basic block analysis optimizes EH return stub away (was: Re: Testsuite Results for gcc-2.96 19990628)

[Richard Henderson]

On Thu, Jul 01, 1999 at 03:16:02PM -0700, Mike Stump wrote:
> :-) Those instructions don't do what you think they do.  :-) I wonder
> if we can add a volatile asm, a memory barrier, or something to keep
> the optimizer from looking at it.

Actually, that wouldn't have helped.  The basic block was being
deleted because it was unreachable.

The expand_eh_return change below is the crucial one.  If we allow
the function to be inlined, we'll collect rtl then finally call
output_inline_function.  Which will call init_function_start, which
calls init_eh_for_function, which zeros eh_return_stub_label, which
disables all the magic in flow.

The other two changes are things I tried on the way to a correct
solution, but they seem like good ideas anyway.  The flow change
to not merge across EH edges can't happen often, but I suspect the
wrong thing would happen if it did.


r~



	* except.c (expand_eh_return): Set current_function_cannot_inline.
	(save_eh_status, restore_eh_status): Twiddle eh_return_stub_label.
	* function.h (struct function): Add eh_return_stub_label.
	* flow.c (delete_unreachable_blocks): Don't merge across EH edges.

Index: except.c
===================================================================
RCS file: /egcs/carton/cvsfiles/egcs/gcc/except.c,v
retrieving revision 1.82
diff -c -p -d -r1.82 except.c
*** except.c	1999/04/15 19:54:09	1.82
--- except.c	1999/07/01 23:38:57
*************** save_eh_status (p)
*** 2446,2451 ****
--- 2446,2452 ----
    p->caught_return_label_stack = caught_return_label_stack;
    p->protect_list = protect_list;
    p->ehc = current_function_ehc;
+   p->eh_return_stub_label = eh_return_stub_label;
  
    init_eh_for_function ();
  }
*************** restore_eh_status (p)
*** 2469,2474 ****
--- 2470,2476 ----
    ehstack = p->ehstack;
    catchstack = p->catchstack;
    current_function_ehc = p->ehc;
+   eh_return_stub_label = p->eh_return_stub_label;
  }
  
  /* This section is for the exception handling specific optimization
*************** expand_eh_return ()
*** 2791,2796 ****
--- 2793,2800 ----
  
    if (!eh_return_context)
      return;
+ 
+   current_function_cannot_inline = 1;
  
    eh_regs (&reg1, &reg2, &reg3, 1);
  #ifdef POINTERS_EXTEND_UNSIGNED
Index: function.h
===================================================================
RCS file: /egcs/carton/cvsfiles/egcs/gcc/function.h,v
retrieving revision 1.18.4.1
diff -c -p -d -r1.18.4.1 function.h
*** function.h	1999/05/30 13:19:42	1.18.4.1
--- function.h	1999/07/01 23:38:57
*************** struct function
*** 146,151 ****
--- 146,152 ----
    struct label_node *caught_return_label_stack;
    tree protect_list;
    rtx ehc;
+   rtx eh_return_stub_label;
  
    /* For expr.c.  */
    rtx pending_chain;
Index: flow.c
===================================================================
RCS file: /egcs/carton/cvsfiles/egcs/gcc/flow.c,v
retrieving revision 1.120.4.2
diff -c -p -d -r1.120.4.2 flow.c
*** flow.c	1999/06/01 21:49:28	1.120.4.2
--- flow.c	1999/07/01 23:38:57
*************** delete_unreachable_blocks ()
*** 1578,1583 ****
--- 1578,1584 ----
        /* A loop because chains of blocks might be combineable.  */
        while ((s = b->succ) != NULL
  	     && s->succ_next == NULL
+ 	     && (s->flags & EDGE_EH) == 0
  	     && (c = s->dest) != EXIT_BLOCK_PTR
  	     && c->pred->pred_next == NULL
  	     && merge_blocks (s, b, c))