Use std::unordered_map<int, int> for StdIntMap.

When using `std::map<int, int>`, profiling shows a hotspot in the iteration in `PrefilterTree::PropagateMatch()`. Application-level benchmarks indicate that changing maps produces a noticeable win. Change-Id: I0a7c43de254642b8ccd188cc93eff4d08d3c10fd Reviewed-on: https://code-review.googlesource.com/c/re2/+/59990 Reviewed-by: Perry Lorier <[email protected]> Reviewed-by: Paul Wankadia <[email protected]>
google · Mar 24, 2022 · 248b65f · 248b65f
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commit 248b65f
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diff --git a/re2/prefilter_tree.cc b/re2/prefilter_tree.cc
@@ -67,7 +67,6 @@ void PrefilterTree::Compile(std::vector<std::string>* atom_vec) {
 
   compiled_ = true;
 
-  // TODO(junyer): Use std::unordered_set<Prefilter*> instead?
   NodeMap nodes;
   AssignUniqueIds(&nodes, atom_vec);
 

diff --git a/re2/prefilter_tree.h b/re2/prefilter_tree.h
@@ -18,6 +18,7 @@
 
 #include <map>
 #include <string>
+#include <unordered_map>
 #include <vector>
 
 #include "util/util.h"
@@ -59,7 +60,9 @@ class PrefilterTree {
 
  private:
   typedef SparseArray<int> IntMap;
-  typedef std::map<int, int> StdIntMap;
+  typedef std::unordered_map<int, int> StdIntMap;
+  // TODO(junyer): Use std::unordered_set<Prefilter*> instead?
+  // It should be trivial to get rid of the stringification...
   typedef std::map<std::string, Prefilter*> NodeMap;
 
   // Each unique node has a corresponding Entry that helps in