Re: Patch to omit dwarf2 unwind info for leaves

[Jason Merrill <jason at cygnus dot com>]

This patch changes the behavior to depend on can_throw directly, for
greater precision.

2000-03-09  Jason Merrill  <jason@casey.cygnus.com>

	* except.c (can_throw): See through a SEQUENCE.
	(nothrow_function_p): New fn.
	* except.h: Declare it.
	* function.c (current_function_nothrow): New var.
	(prepare_function_start): Initialize it.
	* output.h: Declare it.
	* toplev.c (rest_of_compilation): Set it.
	* dwarf2out.c (dwarf2out_begin_prologue): Use it.

Index: except.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/except.c,v
retrieving revision 1.120
diff -c -p -r1.120 except.c
*** except.c	2000/03/08 21:30:17	1.120
--- except.c	2000/03/09 18:29:07
*************** expand_fixup_region_end (cleanup)
*** 1646,1662 ****
  }
  
  /* If we are using the setjmp/longjmp EH codegen method, we emit a
!    call to __sjthrow.
  
-    Otherwise, we emit a call to __throw and note that we threw
-    something, so we know we need to generate the necessary code for
-    __throw.
- 
-    Before invoking throw, the __eh_pc variable must have been set up
-    to contain the PC being thrown from. This address is used by
-    __throw to determine which exception region (if any) is
-    responsible for handling the exception.  */
- 
  void
  emit_throw ()
  {
--- 1646,1653 ----
  }
  
  /* If we are using the setjmp/longjmp EH codegen method, we emit a
!    call to __sjthrow.  Otherwise, we emit a call to __throw.  */
  
  void
  emit_throw ()
  {
*************** static int
*** 2629,2634 ****
--- 2620,2629 ----
  can_throw (insn)
       rtx insn;
  {
+   if (GET_CODE (insn) == INSN
+       && GET_CODE (PATTERN (insn)) == SEQUENCE)
+     insn = XVECEXP (PATTERN (insn), 0, 0);
+ 
    /* Calls can always potentially throw exceptions, unless they have
       a REG_EH_REGION note with a value of 0 or less.  */
    if (GET_CODE (insn) == CALL_INSN)
*************** can_throw (insn)
*** 2647,2652 ****
--- 2642,2665 ----
      }
  
    return 0;
+ }
+ 
+ /* Return nonzero if nothing in this function can throw.  */
+ 
+ int
+ nothrow_function_p ()
+ {
+   rtx insn;
+ 
+   for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
+     if (can_throw (insn))
+       return 0;
+   for (insn = current_function_epilogue_delay_list; insn;
+        insn = XEXP (insn, 1))
+     if (can_throw (insn))
+       return 0;
+ 
+   return 1;
  }
  
  /* Scan a exception region looking for the matching end and then
Index: except.h
===================================================================
RCS file: /cvs/gcc/egcs/gcc/except.h,v
retrieving revision 1.37
diff -c -p -r1.37 except.h
*** except.h	2000/02/26 06:04:48	1.37
--- except.h	2000/03/09 18:29:08
*************** extern struct label_node *outer_context_
*** 427,432 ****
--- 427,436 ----
  
  extern rtx exception_handler_labels;
  
+ /* Return nonzero if nothing in this function can throw.  */
+ 
+ extern int nothrow_function_p			PARAMS ((void));
+ 
  /* Performs optimizations for exception handling, such as removing
     unnecessary exception regions. Invoked from jump_optimize ().  */
  
Index: function.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/function.c,v
retrieving revision 1.172
diff -c -p -r1.172 function.c
*** function.c	2000/03/06 09:50:16	1.172
--- function.c	2000/03/09 18:29:12
*************** Boston, MA 02111-1307, USA.  */
*** 107,112 ****
--- 107,117 ----
     compiler passes. */
  int current_function_is_leaf;
  
+ /* Nonzero if function being compiled doesn't contain any instructions
+    that can throw an exception.  This is set prior to final.  */
+ 
+ int current_function_nothrow;
+ 
  /* Nonzero if function being compiled doesn't modify the stack pointer
     (ignoring the prologue and epilogue).  This is only valid after
     life_analysis has run. */
*************** prepare_function_start ()
*** 5760,5765 ****
--- 5765,5771 ----
    current_function_calls_alloca = 0;
    current_function_contains_functions = 0;
    current_function_is_leaf = 0;
+   current_function_nothrow = 0;
    current_function_sp_is_unchanging = 0;
    current_function_uses_only_leaf_regs = 0;
    current_function_has_computed_jump = 0;
Index: output.h
===================================================================
RCS file: /cvs/gcc/egcs/gcc/output.h,v
retrieving revision 1.44
diff -c -p -r1.44 output.h
*** output.h	2000/03/07 20:39:05	1.44
--- output.h	2000/03/09 18:29:13
*************** extern FILE *asm_out_file;
*** 412,417 ****
--- 412,422 ----
  
  extern int current_function_is_leaf;
  
+ /* Nonzero if function being compiled doesn't contain any instructions
+    that can throw an exception.  This is set prior to final.  */
+ 
+ extern int current_function_nothrow;
+ 
  /* Nonzero if function being compiled doesn't modify the stack pointer
     (ignoring the prologue and epilogue).  This is only valid after
     life_analysis has run. */
Index: toplev.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/toplev.c,v
retrieving revision 1.300
diff -c -p -r1.300 toplev.c
*** toplev.c	2000/03/07 20:39:05	1.300
--- toplev.c	2000/03/09 18:29:16
*************** rest_of_compilation (decl)
*** 3674,3682 ****
  	print_rtl_graph_with_bb (dump_base_name, ".20.stack", insns);
      }
  
!    if (ggc_p)
!      ggc_collect ();
  #endif
  
    /* Now turn the rtl into assembler code.  */
  
--- 3674,3684 ----
  	print_rtl_graph_with_bb (dump_base_name, ".20.stack", insns);
      }
  
!   if (ggc_p)
!     ggc_collect ();
  #endif
+ 
+   current_function_nothrow = nothrow_function_p ();
  
    /* Now turn the rtl into assembler code.  */
  
Index: dwarf2out.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/dwarf2out.c,v
retrieving revision 1.159
diff -c -p -r1.159 dwarf2out.c
*** dwarf2out.c	2000/03/08 23:05:30	1.159
--- dwarf2out.c	2000/03/09 18:29:22
*************** dwarf2out_begin_prologue ()
*** 1890,1897 ****
    fde->dw_fde_end = NULL;
    fde->dw_fde_cfi = NULL;
  
!   /* Normally, only calls can throw, so a leaf function will never throw.  */
!   fde->nothrow = (current_function_is_leaf && !asynchronous_exceptions);
  
    args_size = old_args_size = 0;
  }
--- 1890,1896 ----
    fde->dw_fde_end = NULL;
    fde->dw_fde_cfi = NULL;
  
!   fde->nothrow = current_function_nothrow;
  
    args_size = old_args_size = 0;
  }