SILOptimizer: fix non-deterministic behavior in RedundantLoadElimination and DeadStoreElimination.

Replace some DenseSets, which are used for iteration, with vectors.

SR-8844
rdar://problem/44762620

include/swift/SILOptimizer/Utils/LoadStoreOptUtils.h

@@ -289,7 +289,6 @@ static inline llvm::hash_code hash_value(const LSValue &V) {
 //===----------------------------------------------------------------------===//
 //                            Load Store Location
 //===----------------------------------------------------------------------===//
-using LSLocationSet = llvm::DenseSet<LSLocation>;
 using LSLocationList = llvm::SmallVector<LSLocation, 8>;
 using LSLocationIndexMap = llvm::SmallDenseMap<LSLocation, unsigned, 32>;
 using LSLocationBaseMap = llvm::DenseMap<SILValue, LSLocation>;
@@ -357,7 +356,7 @@ public:
 
   /// Given a set of locations derived from the same base, try to merge/reduce
   /// them into smallest number of LSLocations possible.
-  static bool reduce(LSLocation Base, SILModule *Mod, LSLocationSet &Locs);
+  static void reduce(LSLocation Base, SILModule *Mod, LSLocationList &Locs);
 
   /// Enumerate the given Mem LSLocation.
   static void enumerateLSLocation(SILModule *M, SILValue Mem,

lib/SILOptimizer/Transforms/DeadStoreElimination.cpp

@@ -251,7 +251,7 @@ public:
   SmallBitVector BBDeallocateLocation;
 
   /// The dead stores in the current basic block.
-  llvm::DenseSet<SILInstruction *> DeadStores;
+  llvm::SmallVector<SILInstruction *, 2> DeadStores;
 
   /// Keeps track of what stores to generate after the data flow stabilizes.
   /// these stores come from partial dead stores.
@@ -946,7 +946,7 @@ void DSEContext::processWrite(SILInstruction *I, SILValue Val, SILValue Mem,
   // instruction is dead.
   if (Dead) {
     LLVM_DEBUG(llvm::dbgs() << "Instruction Dead: " << *I << "\n");
-    S->DeadStores.insert(I);
+    S->DeadStores.push_back(I);
     ++NumDeadStores;
     return;
   }
@@ -954,14 +954,14 @@ void DSEContext::processWrite(SILInstruction *I, SILValue Val, SILValue Mem,
   // Partial dead store - stores to some locations are dead, but not all. This
   // is a partially dead store. Also at this point we know what locations are
   // dead.
-  llvm::DenseSet<LSLocation> Alives;
+  LSLocationList Alives;
   if (V.any()) {
     // Take out locations that are dead.
     for (unsigned i = 0; i < V.size(); ++i) {
       if (V.test(i))
         continue;
       // This location is alive.
-      Alives.insert(Locs[i]);
+      Alives.push_back(Locs[i]);
     }
 
     // Try to create as few aggregated stores as possible out of the locations.
@@ -994,7 +994,7 @@ void DSEContext::processWrite(SILInstruction *I, SILValue Val, SILValue Mem,
 
     // Lastly, mark the old store as dead.
     LLVM_DEBUG(llvm::dbgs() << "Instruction Partially Dead: " << *I << "\n");
-    S->DeadStores.insert(I);
+    S->DeadStores.push_back(I);
     ++NumPartialDeadStores;
   }
 }

lib/SILOptimizer/Transforms/RedundantLoadElimination.cpp

@@ -416,8 +416,6 @@ public:
 
 namespace {
 
-using BBValueMap = llvm::DenseMap<SILBasicBlock *, SILValue>;
-
 /// This class stores global state that we use when computing redundant load and
 /// their replacement in each basic block.
 class RLEContext {
@@ -1248,7 +1246,7 @@ BlockState::ValueState BlockState::getValueStateAtEndOfBlock(RLEContext &Ctx,
 
 SILValue RLEContext::computePredecessorLocationValue(SILBasicBlock *BB,
                                                      LSLocation &L) {
-  BBValueMap Values;
+  llvm::SmallVector<std::pair<SILBasicBlock *, SILValue>, 8> Values;
   llvm::DenseSet<SILBasicBlock *> HandledBBs;
   llvm::SmallVector<SILBasicBlock *, 8> WorkList;
 
@@ -1277,7 +1275,7 @@ SILValue RLEContext::computePredecessorLocationValue(SILBasicBlock *BB,
     // locations, collect and reduce them into a single value in the current
     // basic block.
     if (Forwarder.isConcreteValues(*this, L)) {
-      Values[CurBB] = Forwarder.reduceValuesAtEndOfBlock(*this, L);
+      Values.push_back({CurBB, Forwarder.reduceValuesAtEndOfBlock(*this, L)});
       continue;
     }
 
@@ -1301,7 +1299,7 @@ SILValue RLEContext::computePredecessorLocationValue(SILBasicBlock *BB,
 
     // Reduce the available values into a single SILValue we can use to forward
     SILInstruction *IPt = CurBB->getTerminator();
-    Values[CurBB] = LSValue::reduce(L, &BB->getModule(), LSValues, IPt);
+    Values.push_back({CurBB, LSValue::reduce(L, &BB->getModule(), LSValues, IPt)});
   }
 
   // Finally, collect all the values for the SILArgument, materialize it using
@@ -1317,7 +1315,7 @@ SILValue RLEContext::computePredecessorLocationValue(SILBasicBlock *BB,
 bool RLEContext::collectLocationValues(SILBasicBlock *BB, LSLocation &L,
                                        LSLocationValueMap &Values,
                                        ValueTableMap &VM) {
-  LSLocationSet CSLocs;
+  LSLocationList CSLocs;
   LSLocationList Locs;
   LSLocation::expand(L, &BB->getModule(), Locs, TE);
 
@@ -1328,7 +1326,7 @@ bool RLEContext::collectLocationValues(SILBasicBlock *BB, LSLocation &L,
     Values[X] = getValue(VM[getLocationBit(X)]);
     if (!Values[X].isCoveringValue())
       continue;
-    CSLocs.insert(X);
+    CSLocs.push_back(X);
   }
 
   // For locations which we do not have concrete values for in this basic
@@ -1563,7 +1561,7 @@ bool RLEContext::run() {
   processBasicBlocksForRLE(Optimistic);
 
   // Finally, perform the redundant load replacements.
-  llvm::DenseSet<SILInstruction *> InstsToDelete;
+  llvm::SmallVector<SILInstruction *, 16> InstsToDelete;
   bool SILChanged = false;
   for (auto &B : *Fn) {
     auto &State = BBToLocState[&B];
@@ -1587,7 +1585,7 @@ bool RLEContext::run() {
                               << "With " << Iter->second);
       SILChanged = true;
       Iter->first->replaceAllUsesWith(Iter->second);
-      InstsToDelete.insert(Iter->first);
+      InstsToDelete.push_back(Iter->first);
       ++NumForwardedLoads;
     }
   }

lib/SILOptimizer/UtilityPasses/LSLocationPrinter.cpp

@@ -181,7 +181,7 @@ public:
   void printMemReduction(SILFunction &Fn) {
     LSLocation L;
     LSLocationList Locs;
-    llvm::DenseSet<LSLocation> SLocs;
+    LSLocationList SLocs;
     unsigned Counter = 0;
     for (auto &BB : Fn) {
       for (auto &II : BB) {
@@ -212,7 +212,7 @@ public:
         // Reduction should not care about the order of the memory locations in
         // the set.
         for (auto I = Locs.begin(); I != Locs.end(); ++I) {
-          SLocs.insert(*I);
+          SLocs.push_back(*I);
         }
 
         // This should get the original (unexpanded) location back.

lib/SILOptimizer/Utils/LoadStoreOptUtils.cpp

@@ -185,36 +185,62 @@ LSLocation::expand(LSLocation Base, SILModule *M, LSLocationList &Locs,
   }
 }
 
-bool
-LSLocation::reduce(LSLocation Base, SILModule *M, LSLocationSet &Locs) {
+/// Gets the sub-locations of \p Base in \p SubLocations.
+/// Returns false if this is not possible or too complex.
+static bool
+getSubLocations(LSLocationList &SubLocations, LSLocation Base, SILModule *M,
+             const LSLocationList &Locs) {
   // If this is a class reference type, we have reached end of the type tree.
   if (Base.getType(M).getClassOrBoundGenericClass())
-    return Locs.find(Base) != Locs.end();
+    return false;
 
-  // This a don't expand node.
-  if (!shouldExpand(*M, Base.getType(M))) {
-    return Locs.find(Base) != Locs.end();
+  // Don't expand if it would be too complex. As Locs is a list (and not a set)
+  // we want to avoid quadratic complexity in replaceInner().
+  // Usually Locs is small anyway, because we limit expansion to 6 members.
+  // But with deeply nested types we could run in a corner case where Locs is
+  // large.
+  if (!shouldExpand(*M, Base.getType(M)) || Locs.size() >= 8) {
+    return false;
   }
 
   // This is a leaf node.
-  LSLocationList NextLevel;
-  Base.getNextLevelLSLocations(NextLevel, M);
-  if (NextLevel.empty())
-    return Locs.find(Base) != Locs.end();
+  Base.getNextLevelLSLocations(SubLocations, M);
+  return !SubLocations.empty();
+}
 
-  // This is not a leaf node, try to find whether all its children are alive.
+/// Replaces \p SubLocations with \p Base in \p Locs if all sub-locations are
+/// alive, i.e. present in \p Locs.
+static bool
+replaceSubLocations(LSLocation Base, SILModule *M, LSLocationList &Locs,
+                    const LSLocationList &SubLocations) {
+  // Find whether all its children of Base are alive.
   bool Alive = true;
-  for (auto &X : NextLevel) {
-    Alive &= LSLocation::reduce(X, M, Locs);
+  for (auto &X : SubLocations) {
+    // Recurse into the next level.
+    LSLocationList NextInnerLevel;
+    if (getSubLocations(NextInnerLevel, X, M, Locs)) {
+      Alive &= replaceSubLocations(X, M, Locs, NextInnerLevel);
+    } else {
+      Alive &= is_contained(Locs, X);
+    }
   }
 
   // All next level locations are alive, create the new aggregated location.
-  if (Alive) {
-    for (auto &X : NextLevel)
-      Locs.erase(X);
-    Locs.insert(Base);
-  }
-  return Alive;
+  if (!Alive)
+    return false;
+
+  auto newEnd = std::remove_if(Locs.begin(), Locs.end(), [&](const LSLocation &L) {
+    return is_contained(SubLocations, L);
+  });
+  Locs.erase(newEnd, Locs.end());
+  Locs.push_back(Base);
+  return true;
+}
+
+void LSLocation::reduce(LSLocation Base, SILModule *M, LSLocationList &Locs) {
+  LSLocationList SubLocations;
+  if (getSubLocations(SubLocations, Base, M, Locs))
+    replaceSubLocations(Base, M, Locs, SubLocations);
 }
 
 void