re PR rtl-optimization/40445 (g++ void f() { __builtin_unreachable(); })

2009-07-25  David Daney  <ddaney@caviumnetworks.com>

	PR rtl-optimization/40445
	* emit-rtl.c (next_nonnote_insn_bb): New function.
	* rtl.h (next_nonnote_insn_bb): Declare new function.
	* cfgcleanup.c (try_optimize_cfg): Don't remove an empty block
	with no successors that is the successor of the ENTRY_BLOCK.
	Continue from the top after removing an empty fallthrough block.
	* cfgrtl.c (get_last_bb_insn): Call next_nonnote_insn_bb instead
	of next_nonnote_insn.

2009-07-25  David Daney  <ddaney@caviumnetworks.com>

	PR rtl-optimization/40445
	* g++.dg/other/builtin-unreachable-1.C: New testcase.

From-SVN: r150090

7 files changed, 58 insertions, 4 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 54806d1..3c39fb4 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,16 @@
 2009-07-25  David Daney  <ddaney@caviumnetworks.com>
 
+	PR rtl-optimization/40445
+	* emit-rtl.c (next_nonnote_insn_bb): New function.
+	* rtl.h (next_nonnote_insn_bb): Declare new function.
+	* cfgcleanup.c (try_optimize_cfg): Don't remove an empty block
+	with no successors that is the successor of the ENTRY_BLOCK.
+	Continue from the top after removing an empty fallthrough block.
+	* cfgrtl.c (get_last_bb_insn): Call next_nonnote_insn_bb instead
+	of next_nonnote_insn.
+
+2009-07-25  David Daney  <ddaney@caviumnetworks.com>
+
 	* cfgcleanup.c (old_insns_match_p): Handle the case of empty
 	blocks.
 	
diff --git a/gcc/cfgcleanup.c b/gcc/cfgcleanup.c
index 01ddf99..c631907 100644
--- a/gcc/cfgcleanup.c
+++ b/gcc/cfgcleanup.c
@@ -1846,10 +1846,16 @@ try_optimize_cfg (int mode)
 
 	      /* Delete trivially dead basic blocks.  This is either
 		 blocks with no predecessors, or empty blocks with no
-		 successors.  Empty blocks may result from expanding
+		 successors.  However if the empty block with no
+		 successors is the successor of the ENTRY_BLOCK, it is
+		 kept.  This ensures that the ENTRY_BLOCK will have a
+		 successor which is a precondition for many RTL
+		 passes.  Empty blocks may result from expanding
 		 __builtin_unreachable ().  */
 	      if (EDGE_COUNT (b->preds) == 0
-		  || (EDGE_COUNT (b->succs) == 0 && BB_HEAD (b) == BB_END (b)))
+		  || (EDGE_COUNT (b->succs) == 0
+		      && BB_HEAD (b) == BB_END (b)
+		      && single_succ_edge (ENTRY_BLOCK_PTR)->dest != b))
 		{
 		  c = b->prev_bb;
 		  if (dump_file)
@@ -1921,6 +1927,7 @@ try_optimize_cfg (int mode)
 		  delete_basic_block (b);
 		  changed = true;
 		  b = c;
+		  continue;
 		}
 
 	      if (single_succ_p (b)
diff --git a/gcc/cfgrtl.c b/gcc/cfgrtl.c
index 78df3ff..3c877c2 100644
--- a/gcc/cfgrtl.c
+++ b/gcc/cfgrtl.c
@@ -1712,11 +1712,11 @@ get_last_bb_insn (basic_block bb)
     end = tmp;
 
   /* Include any barriers that may follow the basic block.  */
-  tmp = next_nonnote_insn (end);
+  tmp = next_nonnote_insn_bb (end);
   while (tmp && BARRIER_P (tmp))
     {
       end = tmp;
-      tmp = next_nonnote_insn (end);
+      tmp = next_nonnote_insn_bb (end);
     }
 
   return end;
diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index 5b42f4a..21d8434 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -2998,6 +2998,25 @@ next_nonnote_insn (rtx insn)
   return insn;
 }
 
+/* Return the next insn after INSN that is not a NOTE, but stop the
+   search before we enter another basic block.  This routine does not
+   look inside SEQUENCEs.  */
+
+rtx
+next_nonnote_insn_bb (rtx insn)
+{
+  while (insn)
+    {
+      insn = NEXT_INSN (insn);
+      if (insn == 0 || !NOTE_P (insn))
+	break;
+      if (NOTE_INSN_BASIC_BLOCK_P (insn))
+	return NULL_RTX;
+    }
+
+  return insn;
+}
+
 /* Return the previous insn before INSN that is not a NOTE.  This routine does
    not look inside SEQUENCEs.  */
 
diff --git a/gcc/rtl.h b/gcc/rtl.h
index 637c227..d5ae561 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -1626,6 +1626,7 @@ extern rtx previous_insn (rtx);
 extern rtx next_insn (rtx);
 extern rtx prev_nonnote_insn (rtx);
 extern rtx next_nonnote_insn (rtx);
+extern rtx next_nonnote_insn_bb (rtx);
 extern rtx prev_real_insn (rtx);
 extern rtx next_real_insn (rtx);
 extern rtx prev_active_insn (rtx);
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index c982c25..a0e39e3 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2009-07-25  David Daney  <ddaney@caviumnetworks.com>
 
+	PR rtl-optimization/40445
+	* g++.dg/other/builtin-unreachable-1.C: New testcase.
+
+2009-07-25  David Daney  <ddaney@caviumnetworks.com>
+
 	* gcc.dg/builtin-unreachable-4.c: New test.
 
 2009-07-25  Tobias Burnus  <burnus@net-b.de>
diff --git a/gcc/testsuite/g++.dg/other/builtin-unreachable-1.C b/gcc/testsuite/g++.dg/other/builtin-unreachable-1.C
new file mode 100644
index 0000000..f6a5577
--- /dev/null
+++ b/gcc/testsuite/g++.dg/other/builtin-unreachable-1.C
@@ -0,0 +1,11 @@
+// PR c++/40445
+// Check that a function containing only __builtin_unreachable()
+// doesn't ICE.
+
+// { dg-do compile }
+// { dg-options "-O0" }
+const char *
+f (void)
+{
+  __builtin_unreachable ();
+}