[SLP][NFC]Improve aliasing support in SLP, NFC.

No need to store optional boolean in the map, enough to store boolean
directly. Also, we can do preliminary check for instruction and if they
are not simple, mark as aliased without storing this result in the map.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -2982,25 +2982,25 @@ class BoUpSLP {
   /// is invariant in the calling loop.
   bool isAliased(const MemoryLocation &Loc1, Instruction *Inst1,
                  Instruction *Inst2) {
+    if (!Loc1.Ptr || !isSimple(Inst1) || !isSimple(Inst2))
+      return true;
     // First check if the result is already in the cache.
-    AliasCacheKey key = std::make_pair(Inst1, Inst2);
-    std::optional<bool> &result = AliasCache[key];
-    if (result) {
-      return *result;
-    }
-    bool aliased = true;
-    if (Loc1.Ptr && isSimple(Inst1))
-      aliased = isModOrRefSet(BatchAA.getModRefInfo(Inst2, Loc1));
+    AliasCacheKey Key = std::make_pair(Inst1, Inst2);
+    auto It = AliasCache.find(Key);
+    if (It != AliasCache.end())
+      return It->second;
+    bool Aliased = isModOrRefSet(BatchAA.getModRefInfo(Inst2, Loc1));
     // Store the result in the cache.
-    result = aliased;
-    return aliased;
+    AliasCache.try_emplace(Key, Aliased);
+    AliasCache.try_emplace(std::make_pair(Inst2, Inst1), Aliased);
+    return Aliased;
   }
 
   using AliasCacheKey = std::pair<Instruction *, Instruction *>;
 
   /// Cache for alias results.
   /// TODO: consider moving this to the AliasAnalysis itself.
-  DenseMap<AliasCacheKey, std::optional<bool>> AliasCache;
+  DenseMap<AliasCacheKey, bool> AliasCache;
 
   // Cache for pointerMayBeCaptured calls inside AA.  This is preserved
   // globally through SLP because we don't perform any action which