tree-predcom.c (tree_predictive_commoning_loop): Skip loop that only iterates 1 time.

	* tree-predcom.c (tree_predictive_commoning_loop): Skip loop that only
	iterates 1 time.

	gcc/testsuite
	* gfortran.dg/vect/fast-math-mgrid-resid.f: New test string.

From-SVN: r241100

gcc/ChangeLog

 2016-10-13  Bin Cheng  <bin.cheng@arm.com>
 
+	* tree-predcom.c (tree_predictive_commoning_loop): Skip loop that only
+	iterates 1 time.
+
+2016-10-13  Bin Cheng  <bin.cheng@arm.com>
+
 	* tree-vect-loop-manip.c (adjust_vec_debug_stmts): Don't release
 	adjust_vec automatically.
 	(slpeel_add_loop_guard): Remove param cond_expr_stmt_list.  Rename

gcc/testsuite/ChangeLog

 2016-10-13  Bin Cheng  <bin.cheng@arm.com>
 
+	* gfortran.dg/vect/fast-math-mgrid-resid.f: New test string.
+
+2016-10-13  Bin Cheng  <bin.cheng@arm.com>
+
 	* gcc.dg/vect/vect-98.c: Refine test case.
 	* gcc.dg/vect/vect-strided-a-u8-i8-gap2.c: Increase niters.
 	* gcc.dg/vect/vect-strided-u8-i8-gap2.c: Ditto.

gcc/testsuite/gfortran.dg/vect/fast-math-mgrid-resid.f

@@ -42,3 +42,4 @@ C
 ! { dg-final { scan-tree-dump-times "Executing predictive commoning without unrolling" 1 "pcom" { target lp64 } } }
 ! { dg-final { scan-tree-dump-times "Executing predictive commoning without unrolling" 2 "pcom" { target ia32 } } }
 ! { dg-final { scan-tree-dump-times "Predictive commoning failed: no suitable chains" 0 "pcom" } }
+! { dg-final { scan-tree-dump-times "Loop iterates only 1 time, nothing to do" 1 "pcom" } }

gcc/tree-predcom.c

@@ -2465,6 +2465,15 @@ tree_predictive_commoning_loop (struct loop *loop)
   if (dump_file && (dump_flags & TDF_DETAILS))
     fprintf (dump_file, "Processing loop %d\n",  loop->num);
 
+  /* Nothing for predicitive commoning if loop only iterates 1 time.  */
+  if (get_max_loop_iterations_int (loop) == 0)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file, "Loop iterates only 1 time, nothing to do.\n");
+
+      return false;
+    }
+
   /* Find the data references and split them into components according to their
      dependence relations.  */
   auto_vec<loop_p, 3> loop_nest;