Re: tetex mis-compilation fix

[Richard Henderson <rth at cygnus dot com>]

On Wed, Aug 04, 1999 at 01:13:11AM -0600, Jeffrey A Law wrote:
> The fix (of course) is to not delete a jump that potentially has other
> side effects.
> 
> 	* flow.c (delete_unreachable_blocks): Do not call merge_blocks
> 	or tidy_fallthru_edge if the last insn in the block is not
> 	an unconditional jump or a simple conditional jump.

Consider this alternative patch.


r~


	* jump.c (onlyjump_p): New function.
	* rtl.h: Declare it.
	* flow.c (delete_unreachable_blocks): Use onlyjump_p instead
	of condjump_p in calling tidy_fallthru_edge and merge_blocks.

Index: jump.c
===================================================================
RCS file: /egcs/carton/cvsfiles/egcs/gcc/jump.c,v
retrieving revision 1.63
diff -c -p -d -r1.63 jump.c
*** jump.c	1999/08/04 08:19:36	1.63
--- jump.c	1999/08/04 19:58:03
*************** returnjump_p (insn)
*** 3528,3533 ****
--- 3528,3556 ----
    return for_each_rtx (&PATTERN (insn), returnjump_p_1, NULL);
  }
  
+ /* Return true if INSN is a jump that only transfers control and
+    nothing more.  */
+ 
+ int
+ onlyjump_p (insn)
+      rtx insn;
+ {
+   rtx set;
+ 
+   if (GET_CODE (insn) != JUMP_INSN)
+     return 0;
+ 
+   set = single_set (insn);
+   if (set == NULL)
+     return 0;
+   if (GET_CODE (SET_DEST (set)) != PC)
+     return 0;
+   if (side_effects_p (SET_SRC (set)))
+     return 0;
+ 
+   return 1;
+ }
+ 
  #ifdef HAVE_cc0
  
  /* Return 1 if X is an RTX that does nothing but set the condition codes
Index: rtl.h
===================================================================
RCS file: /egcs/carton/cvsfiles/egcs/gcc/rtl.h,v
retrieving revision 1.107
diff -c -p -d -r1.107 rtl.h
*** rtl.h	1999/08/01 12:07:35	1.107
--- rtl.h	1999/08/04 19:58:03
*************** extern int condjump_p			PROTO ((rtx));
*** 1352,1357 ****
--- 1352,1358 ----
  extern rtx condjump_label		PROTO ((rtx));
  extern int simplejump_p			PROTO ((rtx));
  extern int returnjump_p			PROTO ((rtx));
+ extern int onlyjump_p			PROTO ((rtx));
  extern int sets_cc0_p			PROTO ((rtx));
  extern int invert_jump			PROTO ((rtx, rtx));
  extern int rtx_renumbered_equal_p	PROTO ((rtx, rtx));
Index: flow.c
===================================================================
RCS file: /egcs/carton/cvsfiles/egcs/gcc/flow.c,v
retrieving revision 1.127
diff -c -p -d -r1.127 flow.c
*** flow.c	1999/08/04 07:11:26	1.127
--- flow.c	1999/08/04 19:58:03
*************** delete_unreachable_blocks ()
*** 1564,1574 ****
        if ((s = b->succ) != NULL
  	  && s->succ_next == NULL
  	  && s->dest == c
! 	  /* If the last insn is not a normal conditional jump
! 	     (or an unconditional jump), then we can not tidy the
! 	     fallthru edge because we can not delete the jump.  */
! 	  && GET_CODE (b->end) == JUMP_INSN
! 	  && condjump_p (b->end))
  	tidy_fallthru_edge (s, b, c);
      }
  
--- 1564,1572 ----
        if ((s = b->succ) != NULL
  	  && s->succ_next == NULL
  	  && s->dest == c
! 	  /* If the jump insn has side effects, we can't tidy the edge.  */
! 	  && (GET_CODE (b->end) != JUMP_INSN
! 	      || onlyjump_p (b->end)))
  	tidy_fallthru_edge (s, b, c);
      }
  
*************** delete_unreachable_blocks ()
*** 1587,1597 ****
  	     && (s->flags & EDGE_EH) == 0
  	     && (c = s->dest) != EXIT_BLOCK_PTR
  	     && c->pred->pred_next == NULL
! 	     /* If the last insn is not a normal conditional jump
! 		(or an unconditional jump), then we can not merge
! 		the blocks because we can not delete the jump.  */
! 	     && GET_CODE (b->end) == JUMP_INSN
! 	     && condjump_p (b->end)
  	     && merge_blocks (s, b, c))
  	continue;
  
--- 1585,1593 ----
  	     && (s->flags & EDGE_EH) == 0
  	     && (c = s->dest) != EXIT_BLOCK_PTR
  	     && c->pred->pred_next == NULL
! 	     /* If the jump insn has side effects, we can't kill the edge.  */
! 	     && (GET_CODE (b->end) != JUMP_INSN
! 		 || onlyjump_p (b->end))
  	     && merge_blocks (s, b, c))
  	continue;