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From: "steven at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/43631] var-tracking inserts notes with non-NULL BLOCK_FOR_INSN in between basic blocks
Date: Fri, 07 Dec 2012 11:59:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43631

--- Comment #14 from Steven Bosscher <steven at gcc dot gnu.org> 2012-12-07 11:59:15 UTC ---
(In reply to comment #13)
> Please hold on with that, seems BB_END is BARRIER, which is wrong.
> Starting with distilling a testcase...

Perhaps Alex' is right that the real problem is in how BLOCK_FOR_INSN
is handled in add_insn_after and add_insn_before.  Jakub, does the
following make sense to you?

Index: emit-rtl.c
===================================================================
--- emit-rtl.c  (revision 194229)
+++ emit-rtl.c  (working copy)
@@ -3845,19 +3845,25 @@ add_insn_after (rtx insn, rtx after, bas
       gcc_assert (stack);
     }

-  if (!BARRIER_P (after)
-      && !BARRIER_P (insn)
-      && (bb = BLOCK_FOR_INSN (after)))
+  /* If the new insn is a barrier, bb should be NULL because a barrier
+     is never inside a basic block.  Also avoid emitting double barriers.  */
+  if (BARRIER_P (insn))
+    gcc_checking_assert (bb == NULL && !BARRIER_P (after));
+  /* Otherwise, try to deduce a basic block from AFTER.  */
+  else if (!bb
+          && !BARRIER_P (after)
+          && BLOCK_FOR_INSN (after) != NULL
+          && after != BB_END (BLOCK_FOR_INSN (after)))
+    bb = BLOCK_FOR_INSN (after);
+
+  if (bb)
     {
       set_block_for_insn (insn, bb);
       if (INSN_P (insn))
        df_insn_rescan (insn);
-      /* Should not happen as first in the BB is always
-        either NOTE or LABEL.  */
-      if (BB_END (bb) == after
-         /* Avoid clobbering of structure when creating new BB.  */
-         && !BARRIER_P (insn)
-         && !NOTE_INSN_BASIC_BLOCK_P (insn))
+      /* Move BB_END from AFTER to INSN unless INSN is a note (a note cannot
+        be the end a basic block).  */
+      if (BB_END (bb) == after && !NOTE_P (insn))
        BB_END (bb) = insn;
     }