[PATCH] D127070: [ADT][NFC] Early bail out for ComputeEditDistance

[Nathan James via Phabricator via llvm-commits]

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The minimun bound for number of edits is the size difference between the 2 arrays.
If MaxEditDistance is smaller than this, we can bail out early without needing to traverse any of the arrays.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D127070

Files:
  llvm/include/llvm/ADT/edit_distance.h


Index: llvm/include/llvm/ADT/edit_distance.h
===================================================================
--- llvm/include/llvm/ADT/edit_distance.h
+++ llvm/include/llvm/ADT/edit_distance.h
@@ -61,6 +61,15 @@
   typename ArrayRef<T>::size_type m = FromArray.size();
   typename ArrayRef<T>::size_type n = ToArray.size();
 
+  if (MaxEditDistance) {
+    // If the difference in size between the 2 arrays is larger than the max
+    // distance allowed, we can bail out as we will always need at least
+    // MaxEditDistance insertions or removals.
+    typename ArrayRef<T>::size_type AbsDiff = m > n ? m - n : n - m;
+    if (AbsDiff > MaxEditDistance)
+      return MaxEditDistance + 1;
+  }
+
   const unsigned SmallBufferSize = 64;
   unsigned SmallBuffer[SmallBufferSize];
   std::unique_ptr<unsigned[]> Allocated;


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