Use a separate valueenumerator for alias cache and memory behavior cache

If we use a shared valueenumerator, imagine the case when one of the AAcache or MBcache
is cleared and we clear the valueenumerator.

This could give rise to collisions (false positives) in the not-yet-cleared cache!

Author: trentxintong

include/swift/SILOptimizer/Analysis/AliasAnalysis.h

@@ -112,12 +112,19 @@ class AliasAnalysis : public SILAnalysis {
   /// The computeMemoryBehavior() method uses this map to cache queries.
   llvm::DenseMap<MemBehaviorKeyTy, MemoryBehavior> MemoryBehaviorCache;
 
-  /// The AliasAnalysis/MemoryBehavior cache can't directly map a pair of
-  /// ValueBase pointers to alias/memorybehavior results because we'd like to
-  /// be able to remove deleted pointers without having to scan the whole map.
-  /// So, instead of storing pointers we map pointers to indices and store the
-  /// indices.
-  ValueEnumerator<ValueBase*> ValueBaseToIndex;
+  /// The AliasAnalysis cache can't directly map a pair of ValueBase pointers
+  /// to alias results because we'd like to be able to remove deleted pointers
+  /// without having to scan the whole map. So, instead of storing pointers we
+  /// map pointers to indices and store the indices.
+  ValueEnumerator<ValueBase*> AliasValueBaseToIndex;
+  
+  /// Same as AliasValueBaseToIndex, map a pointer to the indices for
+  /// MemoryBehaviorCache.
+  ///
+  /// NOTE: we do not use the same ValueEnumerator for the alias cache, 
+  /// as when either cache is cleared, we can not clear the ValueEnumerator
+  /// because doing so could give rise to collisions in the other cache.
+  ValueEnumerator<ValueBase*> MemoryBehaviorValueBaseToIndex;
 
   AliasResult aliasAddressProjection(SILValue V1, SILValue V2,
                                      SILValue O1, SILValue O2);
@@ -134,7 +141,8 @@ class AliasAnalysis : public SILAnalysis {
     // The pointer I is going away.  We can't scan the whole cache and remove
     // all of the occurrences of the pointer. Instead we remove the pointer
     // from the cache the translates pointers to indices.
-    ValueBaseToIndex.invalidateValue(I);
+    AliasValueBaseToIndex.invalidateValue(I);
+    MemoryBehaviorValueBaseToIndex.invalidateValue(I);
   }
 
   virtual bool needsNotifications() override { return true; }

lib/SILOptimizer/Analysis/AliasAnalysis.cpp

@@ -539,7 +539,7 @@ AliasResult AliasAnalysis::alias(SILValue V1, SILValue V2,
   // Flush the cache if the size of the cache is too large.
   if (AliasCache.size() > AliasAnalysisMaxCacheSize) {
     AliasCache.clear();
-    ValueBaseToIndex.clear();
+    AliasValueBaseToIndex.clear();
   }
 
   // Calculate the aliasing result and store it in the cache.
@@ -710,8 +710,8 @@ SILAnalysis *swift::createAliasAnalysis(SILModule *M) {
 
 AliasKeyTy AliasAnalysis::toAliasKey(SILValue V1, SILValue V2,
                                      SILType Type1, SILType Type2) {
-  size_t idx1 = ValueBaseToIndex.getIndex(V1.getDef());
-  size_t idx2 = ValueBaseToIndex.getIndex(V2.getDef());
+  size_t idx1 = AliasValueBaseToIndex.getIndex(V1.getDef());
+  size_t idx2 = AliasValueBaseToIndex.getIndex(V2.getDef());
   unsigned R1 = V1.getResultNumber();
   unsigned R2 = V2.getResultNumber();
   void *t1 = Type1.getOpaqueValue();

lib/SILOptimizer/Analysis/MemoryBehavior.cpp

@@ -313,7 +313,7 @@ AliasAnalysis::computeMemoryBehavior(SILInstruction *Inst, SILValue V,
   // Flush the cache if the size of the cache is too large.
   if (MemoryBehaviorCache.size() > MemoryBehaviorAnalysisMaxCacheSize) {
     MemoryBehaviorCache.clear();
-    ValueBaseToIndex.clear();
+    MemoryBehaviorValueBaseToIndex.clear();
   }
 
   // Calculate the aliasing result and store it in the cache.
@@ -333,8 +333,8 @@ AliasAnalysis::computeMemoryBehaviorInner(SILInstruction *Inst, SILValue V,
 
 MemBehaviorKeyTy AliasAnalysis::toMemoryBehaviorKey(SILValue V1, SILValue V2,
                                                     RetainObserveKind M) {
-  size_t idx1 = ValueBaseToIndex.getIndex(V1.getDef());
-  size_t idx2 = ValueBaseToIndex.getIndex(V2.getDef());
+  size_t idx1 = MemoryBehaviorValueBaseToIndex.getIndex(V1.getDef());
+  size_t idx2 = MemoryBehaviorValueBaseToIndex.getIndex(V2.getDef());
   unsigned R2 = V2.getResultNumber();
   return {idx1, idx2, R2, M};
 }