Precompute bit_state_text_max_size during compilation.

Change-Id: I293d8229b74486e4196eb1a3c8e455b3ae2f098c Reviewed-on: https://code-review.googlesource.com/c/re2/+/59410 Reviewed-by: Perry Lorier <[email protected]> Reviewed-by: Paul Wankadia <[email protected]>
google · Oct 28, 2021 · 0dade9f · 0dade9f
1 parent 7424791
commit 0dade9f
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Showing 3 changed files with 17 additions and 14 deletions.
diff --git a/re2/prog.cc b/re2/prog.cc
@@ -118,6 +118,7 @@ Prog::Prog()
     prefix_foldcase_(false),
     prefix_size_(0),
     list_count_(0),
+    bit_state_text_max_size_(0),
     dfa_mem_(0),
     dfa_first_(NULL),
     dfa_longest_(NULL) {
@@ -640,6 +641,11 @@ void Prog::Flatten() {
     for (int i = 0; i < list_count_; ++i)
       list_heads_[flatmap[i]] = i;
   }
+
+  // BitState allocates a bitmap of size list_count_ * (text.size()+1)
+  // for tracking pairs of possibilities that it has already explored.
+  const size_t kBitStateBitmapMaxSize = 256*1024;  // max size in bits
+  bit_state_text_max_size_ = kBitStateBitmapMaxSize / list_count_ - 1;
 }
 
 void Prog::MarkSuccessors(SparseArray<int>* rootmap,

diff --git a/re2/prog.h b/re2/prog.h
@@ -207,6 +207,7 @@ class Prog {
   int list_count() { return list_count_; }
   int inst_count(InstOp op) { return inst_count_[op]; }
   uint16_t* list_heads() { return list_heads_.data(); }
+  size_t bit_state_text_max_size() { return bit_state_text_max_size_; }
   int64_t dfa_mem() { return dfa_mem_; }
   void set_dfa_mem(int64_t dfa_mem) { dfa_mem_ = dfa_mem; }
   bool anchor_start() { return anchor_start_; }
@@ -429,10 +430,11 @@ class Prog {
     };
   };
 
-  int list_count_;                 // count of lists (see above)
-  int inst_count_[kNumInst];       // count of instructions by opcode
-  PODArray<uint16_t> list_heads_;  // sparse array enumerating list heads
-                                   // not populated if size_ is overly large
+  int list_count_;                  // count of lists (see above)
+  int inst_count_[kNumInst];        // count of instructions by opcode
+  PODArray<uint16_t> list_heads_;   // sparse array enumerating list heads
+                                    // not populated if size_ is overly large
+  size_t bit_state_text_max_size_;  // upper bound (inclusive) on text.size()
 
   PODArray<Inst> inst_;              // pointer to instruction array
   PODArray<uint8_t> onepass_nodes_;  // data for OnePass nodes

diff --git a/re2/re2.cc b/re2/re2.cc
@@ -690,15 +690,9 @@ bool RE2::Match(const StringPiece& text,
   if (options_.longest_match())
     kind = Prog::kLongestMatch;
 
-  bool can_one_pass = (is_one_pass_ && ncap <= Prog::kMaxOnePassCapture);
-
-  // BitState allocates a bitmap of size prog_->list_count() * text.size().
-  // It also allocates a stack of 3-word structures which could potentially
-  // grow as large as prog_->list_count() * text.size(), but in practice is
-  // much smaller.
-  const int kMaxBitStateBitmapSize = 256*1024;  // bitmap size <= max (bits)
+  bool can_one_pass = is_one_pass_ && ncap <= Prog::kMaxOnePassCapture;
   bool can_bit_state = prog_->CanBitState();
-  size_t bit_state_text_max = kMaxBitStateBitmapSize / prog_->list_count();
+  size_t bit_state_text_max_size = prog_->bit_state_text_max_size();
 
 #ifdef RE2_HAVE_THREAD_LOCAL
   hooks::context = this;
@@ -805,7 +799,8 @@ bool RE2::Match(const StringPiece& text,
         skipped_test = true;
         break;
       }
-      if (can_bit_state && text.size() <= bit_state_text_max && ncap > 1) {
+      if (can_bit_state && text.size() <= bit_state_text_max_size &&
+          ncap > 1) {
         skipped_test = true;
         break;
       }
@@ -852,7 +847,7 @@ bool RE2::Match(const StringPiece& text,
           LOG(ERROR) << "SearchOnePass inconsistency";
         return false;
       }
-    } else if (can_bit_state && subtext1.size() <= bit_state_text_max) {
+    } else if (can_bit_state && subtext1.size() <= bit_state_text_max_size) {
       if (!prog_->SearchBitState(subtext1, text, anchor,
                                  kind, submatch, ncap)) {
         if (!skipped_test && options_.log_errors())