re PR middle-end/64491 (incorrect warning: loop exit may only be reached after undefined behavior)

Fix PR64491

2015-03-18  Andrew Stubbs  <ams@codesourcery.com>

	PR middle-end/64491
	Revert:
	2014-11-20  Andrew Stubbs  <ams@codesourcery.com>

	* tree-ssa-loop-niter.c (maybe_lower_iteration_bound): Warn if a loop
	condition would be removed due to undefined behaviour.

2015-03-18  Andrew Stubbs  <ams@codesourcery.com>

	PR middle-end/64491
	Revert:
	2014-11-20  Andrew Stubbs  <ams@codesourcery.com>

	* gcc.dg/undefined-loop-1.c: New file.
	* gcc.dg/undefined-loop-2.c: New file.

	2014-12-24  Andrew Stubbs  <ams@codesourcery.com>

	PR testsuite/64032
	* gcc.dg/undefined-loop-2.c: Don't allow GCC to optimize away the
	loop exits too early.

From-SVN: r221492

gcc/ChangeLog

+2015-03-18  Andrew Stubbs  <ams@codesourcery.com>
+
+	PR middle-end/64491
+	Revert:
+	2014-11-20  Andrew Stubbs  <ams@codesourcery.com>
+
+	* tree-ssa-loop-niter.c (maybe_lower_iteration_bound): Warn if a loop
+	condition would be removed due to undefined behaviour.
+
 2015-03-18  Martin Liska  <mliska@suse.cz>
 
 	PR ipa/65432

gcc/testsuite/ChangeLog

+2015-03-18  Andrew Stubbs  <ams@codesourcery.com>
+
+	PR middle-end/64491
+	Revert:
+	2014-11-20  Andrew Stubbs  <ams@codesourcery.com>
+
+	* gcc.dg/undefined-loop-1.c: New file.
+	* gcc.dg/undefined-loop-2.c: New file.
+
+	2014-12-24  Andrew Stubbs  <ams@codesourcery.com>
+
+	PR testsuite/64032
+	* gcc.dg/undefined-loop-2.c: Don't allow GCC to optimize away the
+	loop exits too early.
+
 2015-03-18  Jakub Jelinek  <jakub@redhat.com>
 
 	PR tree-optimization/65450

gcc/testsuite/gcc.dg/undefined-loop-1.c

-/* Check that loops whose final iteration is undefined are detected.  */
-/* { dg-do compile } */
-/* { dg-options "-O2 -Waggressive-loop-optimizations" } */
-
-void doSomething(char);
-
-char array[5];
-
-void
-foo (void)
-{
-  int i;
-  for (i = 0;
-       array[i]  /* { dg-message "note: possible undefined statement is here" } */
-       && i < 5; /* { dg-warning "loop exit may only be reached after undefined behavior" } */
-       i++)
-    doSomething(array[i]);
-}

gcc/testsuite/gcc.dg/undefined-loop-2.c

-/* Check that loops whose final iteration is undefined are detected.  */
-/* { dg-do compile } */
-/* { dg-options "-O2 -Waggressive-loop-optimizations" } */
-
-void doSomething(char);
-
-char array1[5];
-char array2[5];
-
-void
-foo (int p)
-{
-  int i;
-  for (i=0;
-       (p
-        ? array1[i]  /* { dg-message "note: possible undefined statement is here" } */
-        : array2[i]) /* { dg-message "note: possible undefined statement is here" } */
-       && i < 100;   /* { dg-warning "loop exit may only be reached after undefined behavior" } */
-       i++)
-    {
-      if (i >= 5)    /* { dg-warning "loop exit may only be reached after undefined behavior" } */
-	break;
-      doSomething(array1[i]);
-    }
-}

gcc/tree-ssa-loop-niter.c

@@ -3329,7 +3329,6 @@ maybe_lower_iteration_bound (struct loop *loop)
   struct nb_iter_bound *elt;
   bool found_exit = false;
   vec<basic_block> queue = vNULL;
-  vec<gimple> problem_stmts = vNULL;
   bitmap visited;
 
   /* Collect all statements with interesting (i.e. lower than
@@ -3375,7 +3374,6 @@ maybe_lower_iteration_bound (struct loop *loop)
 	  if (not_executed_last_iteration->contains (stmt))
 	    {
 	      stmt_found = true;
-	      problem_stmts.safe_push (stmt);
 	      break;
 	    }
 	  if (gimple_has_side_effects (stmt))
@@ -3419,53 +3417,10 @@ maybe_lower_iteration_bound (struct loop *loop)
 		 "undefined statement must be executed at the last iteration.\n");
       record_niter_bound (loop, loop->nb_iterations_upper_bound - 1,
 			  false, true);
-
-      if (warn_aggressive_loop_optimizations)
-	{
-	  bool exit_warned = false;
-	  for (elt = loop->bounds; elt; elt = elt->next)
-	    {
-	      if (elt->is_exit
-		  && wi::gtu_p (elt->bound, loop->nb_iterations_upper_bound))
-		{
-		  basic_block bb = gimple_bb (elt->stmt);
-		  edge exit_edge = EDGE_SUCC (bb, 0);
-		  struct tree_niter_desc niter;
-
-		  if (!loop_exit_edge_p (loop, exit_edge))
-		    exit_edge = EDGE_SUCC (bb, 1);
-
-		  if(number_of_iterations_exit (loop, exit_edge,
-						&niter, false, false)
-		     && integer_onep (niter.assumptions)
-		     && integer_zerop (niter.may_be_zero)
-		     && niter.niter
-		     && TREE_CODE (niter.niter) == INTEGER_CST
-		     && wi::ltu_p (loop->nb_iterations_upper_bound,
-				   wi::to_widest (niter.niter)))
-		   {
-		     if (warning_at (gimple_location (elt->stmt),
-				     OPT_Waggressive_loop_optimizations,
-				     "loop exit may only be reached after undefined behavior"))
-		       exit_warned = true;
-		   }
-		}
-	    }
-
-	  if (exit_warned && !problem_stmts.is_empty ())
-	    {
-	      gimple stmt;
-	      int index;
-	      FOR_EACH_VEC_ELT (problem_stmts, index, stmt)
-		inform (gimple_location (stmt),
-			"possible undefined statement is here");
-	    }
-      }
     }
 
   BITMAP_FREE (visited);
   queue.release ();
-  problem_stmts.release ();
   delete not_executed_last_iteration;
 }