1 files changed, 22 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index 7582dd8a067..fe8697e31eb 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -51,6 +51,9 @@ STATISTIC(NumCacheCompleteNonLocalPtr,
 // Limit for the number of instructions to scan in a block.
 static const int BlockScanLimit = 100;
 
+// Limit on the number of memdep results to process.
+static const int NumResultsLimit = 100;
+
 char MemoryDependenceAnalysis::ID = 0;
 
 // Register this pass...
@@ -1133,6 +1136,25 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
   while (!Worklist.empty()) {
     BasicBlock *BB = Worklist.pop_back_val();
 
+    // If we do process a large number of blocks it becomes very expensive and
+    // likely it isn't worth worrying about
+    if (Result.size() > NumResultsLimit) {
+      Worklist.clear();
+      // Sort it now (if needed) so that recursive invocations of
+      // getNonLocalPointerDepFromBB and other routines that could reuse the
+      // cache value will only see properly sorted cache arrays.
+      if (Cache && NumSortedEntries != Cache->size()) {
+        SortNonLocalDepInfoCache(*Cache, NumSortedEntries);
+        NumSortedEntries = Cache->size();
+      }
+      // Since we bail out, the "Cache" set won't contain all of the
+      // results for the query.  This is ok (we can still use it to accelerate
+      // specific block queries) but we can't do the fastpath "return all
+      // results from the set".  Clear out the indicator for this.
+      CacheInfo->Pair = BBSkipFirstBlockPair();
+      return true;
+    }
+
     // Skip the first block if we have it.
     if (!SkipFirstBlock) {
       // Analyze the dependency of *Pointer in FromBB.  See if we already have