Improve the performance of typo correction, by using a simple

computation to compute the lower bound of the edit distance, so that
we can avoid computing the edit distance for names that will clearly
be rejected later. Since edit distance is such an expensive algorithm
(M x N), this leads to a 7.5x speedup when correcting NSstring ->
NSString in the presence of a Cocoa PCH.

llvm-svn: 116849

1 files changed, 6 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 6cd0207c800..de581fc6c60 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -2730,6 +2730,12 @@ void TypoCorrectionConsumer::FoundDecl(NamedDecl *ND, NamedDecl *Hiding,
 }
 
 void TypoCorrectionConsumer::FoundName(llvm::StringRef Name) {
+  // Use a simple length-based heuristic to determine the minimum possible
+  // edit distance. If the minimum isn't good enough, bail out early.
+  unsigned MinED = abs((int)Name.size() - (int)Typo.size());
+  if (MinED > BestEditDistance || (MinED && Typo.size() / MinED < 3))
+    return;
+  
   // Compute the edit distance between the typo and the name of this
   // entity. If this edit distance is not worse than the best edit
   // distance we've seen so far, add it to the list of results.