From 08bf909e2b23f6bb092a1098e951a36945f0a659 Mon Sep 17 00:00:00 2001
From: Justin Viiret <justin.viiret@intel.com>
Date: Tue, 6 Jun 2017 14:37:18 +1000
Subject: [PATCH] ng_violet: make calcSplitRatio operation faster

Implements count_reachable in a less malloc-happy way, improving
compile performance. Adds a count() function to small_color_map.
---
 src/nfagraph/ng_violet.cpp       | 28 ++++++++++++++++++++--------
 src/util/graph_small_color_map.h | 17 ++++++++++++++++-
 2 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/src/nfagraph/ng_violet.cpp b/src/nfagraph/ng_violet.cpp
index 9ce732c2..78d73082 100644
--- a/src/nfagraph/ng_violet.cpp
+++ b/src/nfagraph/ng_violet.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2017, Intel Corporation
+ * Copyright (c) 2016-2018, Intel Corporation
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -60,6 +60,7 @@
 #include "util/flat_containers.h"
 #include "util/graph.h"
 #include "util/graph_range.h"
+#include "util/graph_small_color_map.h"
 #include "util/insertion_ordered.h"
 #include "util/make_unique.h"
 #include "util/order_check.h"
@@ -133,14 +134,21 @@ bool createsTransientLHS(const NGHolder &g, const vector<NFAVertex> &vv,
     return true;
 }
 
+/**
+ * Counts the number of vertices that are reachable from the set of sources
+ * given.
+ */
 static
-double calcSplitRatio(const NGHolder &g, const vector<NFAVertex> &vv) {
-    flat_set<NFAVertex> not_reachable;
-    find_unreachable(g, vv, &not_reachable);
-    double rv = (double)not_reachable.size() / num_vertices(g);
-    rv = rv > 0.5 ? 1 - rv : rv;
+size_t count_reachable(const NGHolder &g, const vector<NFAVertex> &sources,
+                small_color_map<decltype(get(vertex_index, g))> &color_map) {
+    auto null_visitor = boost::make_dfs_visitor(boost::null_visitor());
+    color_map.fill(small_color::white);
 
-    return rv;
+    for (auto v : sources) {
+        boost::depth_first_visit(g, v, null_visitor, color_map);
+    }
+
+    return color_map.count(small_color::black);
 }
 
 static
@@ -687,8 +695,12 @@ unique_ptr<VertLitInfo> findBestSplit(const NGHolder &g,
     }
 
     if (last_chance) {
+        const size_t num_verts = num_vertices(g);
+        auto color_map = make_small_color_map(g);
         for (auto &a : lits) {
-            a->split_ratio = calcSplitRatio(g, a->vv);
+            size_t num_reachable = count_reachable(g, a->vv, color_map);
+            double ratio = (double)num_reachable / (double)num_verts;
+            a->split_ratio = ratio > 0.5 ? 1 - ratio : ratio;
         }
     }
 
diff --git a/src/util/graph_small_color_map.h b/src/util/graph_small_color_map.h
index 03e61cf4..249b7153 100644
--- a/src/util/graph_small_color_map.h
+++ b/src/util/graph_small_color_map.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, Intel Corporation
+ * Copyright (c) 2017-2018, Intel Corporation
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -114,6 +114,21 @@ public:
         std::memset(data->data(), val, data->size());
     }
 
+    size_t count(small_color color) const {
+        assert(static_cast<u8>(color) < sizeof(fill_lut));
+        size_t num = 0;
+        for (size_t i = 0; i < n; i++) {
+            size_t byte = i / entries_per_byte;
+            assert(byte < data->size());
+            size_t bit = (i % entries_per_byte) * bit_size;
+            u8 val = ((*data)[byte] >> bit) & bit_mask;
+            if (static_cast<small_color>(val) == color) {
+                num++;
+            }
+        }
+        return num;
+    }
+
     small_color get_impl(key_type key) const {
         auto i = get(index_map, key);
         assert(i < n);