Add param for bb limit to invoke fast_vrp.

If the basic block count is too high, simply use fast_vrp for all
VRP passes.

	* doc/invoke.texi (vrp-block-limit): Document.
	* params.opt (param=vrp-block-limit): New.
	* tree-vrp.cc (fvrp_folder::execute): Invoke fast_vrp if block
	count exceeds limit.

1 files changed, 12 insertions, 2 deletions

diff --git a/gcc/tree-vrp.cc b/gcc/tree-vrp.cc
index 26979b7..e184e9a 100644
--- a/gcc/tree-vrp.cc
+++ b/gcc/tree-vrp.cc
@@ -60,6 +60,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "ipa-cp.h"
 #include "ipa-prop.h"
 #include "attribs.h"
+#include "diagnostic-core.h"
 
 // This class is utilized by VRP and ranger to remove __builtin_unreachable
 // calls, and reflect any resulting global ranges.
@@ -1331,9 +1332,18 @@ public:
   unsigned int execute (function *fun) final override
     {
       // Check for fast vrp.
-      if (&data == &pass_data_fast_vrp)
+      bool use_fvrp = (&data == &pass_data_fast_vrp);
+      if (!use_fvrp && last_basic_block_for_fn (fun) > param_vrp_block_limit)
+	{
+	  use_fvrp = true;
+	  warning (OPT_Wdisabled_optimization,
+		   "Using fast VRP algorithm. %d basic blocks"
+		   " exceeds %<--param=vrp-block-limit=%d%> limit",
+		   n_basic_blocks_for_fn (fun),
+		   param_vrp_block_limit);
+	}
+      if (use_fvrp)
 	return execute_fast_vrp (fun, final_p);
-
       return execute_ranger_vrp (fun, final_p);
     }