Dump a diagnostic info when the insn-to-mem ratio is too small.

2010-05-07  Changpeng Fang  <changpeng.fang@amd.com>

	* tree-ssa-loop-prefetch.c (is_loop_prefetching_profitable): Dump
	a diagnostic info when the insn-to-mem ratio is too small.

From-SVN: r159161

gcc/ChangeLog

+2010-05-07  Changpeng Fang  <changpeng.fang@amd.com>
+
+	* tree-ssa-loop-prefetch.c (is_loop_prefetching_profitable): Dump
+	a diagnostic info when the insn-to-mem ratio is too small.
+
 2010-05-07  Richard Guenther <rguenther@suse.de>
 
 	* gcc.c (LINK_COMMAND_SPEC): Provide a resolution file to

gcc/tree-ssa-loop-prefetch.c

@@ -1551,7 +1551,13 @@ is_loop_prefetching_profitable (unsigned ahead, HOST_WIDE_INT est_niter,
   insn_to_mem_ratio = ninsns / mem_ref_count;
 
   if (insn_to_mem_ratio < PREFETCH_MIN_INSN_TO_MEM_RATIO)
-    return false;
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+        fprintf (dump_file,
+		 "Not prefetching -- instruction to memory reference ratio (%d) too small\n",
+		 insn_to_mem_ratio);
+      return false;
+    }
 
   /* Profitability of prefetching is highly dependent on the trip count.
      For a given AHEAD distance, the first AHEAD iterations do not benefit