[PATCH] D137601: Only hash the start of keys in StringMap

[Jamie Hill-Daniel via Phabricator via llvm-commits]

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Hashing large constant blobs results in long compile times - hash only up to 1024 bytes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D137601

Files:
  llvm/lib/Support/StringMap.cpp


Index: llvm/lib/Support/StringMap.cpp
===================================================================
--- llvm/lib/Support/StringMap.cpp
+++ llvm/lib/Support/StringMap.cpp
@@ -84,7 +84,7 @@
   // Hash table unallocated so far?
   if (NumBuckets == 0)
     init(16);
-  unsigned FullHashValue = djbHash(Name, 0);
+  unsigned FullHashValue = djbHash(Name.take_front(1024), 0);
   unsigned BucketNo = FullHashValue & (NumBuckets - 1);
   unsigned *HashTable = getHashTable(TheTable, NumBuckets);
 
@@ -139,7 +139,8 @@
 int StringMapImpl::FindKey(StringRef Key) const {
   if (NumBuckets == 0)
     return -1; // Really empty table?
-  unsigned FullHashValue = djbHash(Key, 0);
+
+  unsigned FullHashValue = djbHash(Key.take_front(1024), 0);
   unsigned BucketNo = FullHashValue & (NumBuckets - 1);
   unsigned *HashTable = getHashTable(TheTable, NumBuckets);
 


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