Re: Another bootstrap failure on vax: label referred to in addr_vec deleted when basic block is moved to the fallthru position a

["John David Anglin" <dave at hiauly1 dot hia dot nrc dot ca>]

> > Clearly, the label shouldn't have been deleted because there were still
> > references to it in the addr_diff_vec.
> This is weird.
> If there is jumptable juping to the label, there should be edge that prevents
> label from being deleted.
> Moment - is it the case where fallthru edge of jump table and one of
> destinations gets identical?  In that case CFG code sees the edge as "FALLHTUR"
> and don't consider need to keep the label.
> 
> The code checks for posibility of conditional jumps with equivalent destinations:
> 
> 	  if (b->pred->pred_next == NULL
> 	      && (b->pred->flags & EDGE_FALLTHRU)
> 	      && !(b->pred->flags & EDGE_COMPLEX)
> 	      && GET_CODE (b->head) == CODE_LABEL
> 	      && (!(mode & CLEANUP_PRE_SIBCALL)
> 		  || !tail_recursion_label_p (b->head))
> 	      /* If previous block ends with condjump jumping to next BB,
> 	         we can't delete the label.  */
> 	      && (b->pred->src == ENTRY_BLOCK_PTR
> 		  || !reg_mentioned_p (b->head, b->pred->src->end)))
> Here we need to add something like:
> 	      && (!tablejump_p (b->pred->src->end)
> 		  || !reg_mentioned_p (b->head, NEXT_INSN (JUMP_LABEL (b->pred->src->end))))
> 
> I will try to send full patch tomorrow, but today I must leave.

Enclosed is the patch that I worked out to fix the problem.  However, in
testing, I hit new problems:

1) vax:

stage1/xgcc -Bstage1/ -B/usr/local/vax-dec-ultrix4.3/bin/ -c  -DIN_GCC    -g -O2 -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wtraditional -pedantic -Wno-long-long  -DHAVE_CONFIG_H    -I. -I. -I../../gcc -I../../gcc/. -I../../gcc/config -I../../gcc/../include ../../gcc/cpplex.c -o cpplex.o
../../gcc/cpplex.c: In function `cpp_parse_escape':
../../gcc/cpplex.c:1980: Internal compiler error in fixup_var_refs_1, at function.c:1932

2) pa:

gcc -o c++filt  -DIN_GCC    -g  -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wtraditional -pedantic -Wno-long-long  -DHAVE_CONFIG_H  \
  cxxmain.o underscore.o obstack.o  -lintl     ../libiberty/libiberty.a
cd ../../gcc && makeinfo   -I doc -I doc/include -o doc/cpp.info doc/cpp.texi
cd ../../gcc && makeinfo   -I doc -I doc/include -o doc/gcc.info doc/gcc.texi
doc/invoke.texi:3417: No matching `@end table'.
makeinfo: Removing output file `doc/gcc.info' due to errors; use --force to preserve.

I don't think I will get any more time this weekend to work on these problems.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6605)

2001-09-28  John David Anglin  <dave@hiauly1.hia.nrc.ca>

	* cfgcleanup.c (label_mentioned_p): New function.
	(try_optimize_cfg): Use it.

--- cfgcleanup.c.orig	Fri Sep 21 18:29:23 2001
+++ cfgcleanup.c	Fri Sep 28 16:09:38 2001
@@ -52,6 +52,7 @@
 						 rtx *, rtx *));
 
 static bool delete_unreachable_blocks	PARAMS ((void));
+static bool label_mentioned_p		PARAMS ((rtx, rtx));
 static bool tail_recursion_label_p	PARAMS ((rtx));
 static void merge_blocks_move_predecessor_nojumps PARAMS ((basic_block,
 							  basic_block));
@@ -248,6 +249,22 @@
   return changed;
 }
 
+/* Return true if LABEL is mentioned in any insn from INSN up to
+   but not including the label.  */
+
+static bool
+label_mentioned_p (label, insn)
+     rtx label, insn;
+{
+  rtx x;
+
+  for (x = insn; x != label; x = NEXT_INSN (x))
+    if (reg_mentioned_p (label, x))
+      return true;
+
+  return false;
+}
+
 /* Return true if LABEL is used for tail recursion.  */
 
 static bool
@@ -1096,7 +1113,7 @@
 	      /* If previous block ends with condjump jumping to next BB,
 	         we can't delete the label.  */
 	      && (b->pred->src == ENTRY_BLOCK_PTR
-		  || !reg_mentioned_p (b->head, b->pred->src->end)))
+		  || !label_mentioned_p (b->head, b->pred->src->end)))
 	    {
 	      rtx label = b->head;
 	      b->head = NEXT_INSN (b->head);