[SLP][NFC]Improve compile time by storing all nodes for the given

scalar.

No need to scan the whole graph when trying to find matching node for
the scalar, vectorized in several nodes, better to store corresponding
nodes along and scan just this small list.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -2918,7 +2918,7 @@ class BoUpSLP {
                "Scalar already in tree!");
         if (TE) {
           if (TE != Last)
-            MultiNodeScalars.insert(V);
+            MultiNodeScalars.try_emplace(V).first->getSecond().push_back(Last);
           continue;
         }
         ScalarToTreeEntry[V] = Last;
@@ -2979,8 +2979,9 @@ class BoUpSLP {
   /// Maps a specific scalar to its tree entry.
   SmallDenseMap<Value *, TreeEntry *> ScalarToTreeEntry;
 
-  /// List of scalars, used in several vectorize nodes.
-  SmallDenseSet<Value *> MultiNodeScalars;
+  /// List of scalars, used in several vectorize nodes, and the list of the
+  /// nodes.
+  SmallDenseMap<Value *, SmallVector<TreeEntry *>> MultiNodeScalars;
 
   /// Maps a value to the proposed vectorizable size.
   SmallDenseMap<Value *, unsigned> InstrElementSize;
@@ -9866,15 +9867,16 @@ Value *BoUpSLP::vectorizeOperand(TreeEntry *E, unsigned NodeIdx) {
     };
     TreeEntry *VE = getTreeEntry(S.OpValue);
     bool IsSameVE = VE && CheckSameVE(VE);
-    if (!IsSameVE && MultiNodeScalars.contains(S.OpValue)) {
-      auto *I =
-          find_if(VectorizableTree, [&](const std::unique_ptr<TreeEntry> &TE) {
-            return TE->State != TreeEntry::NeedToGather && TE.get() != VE &&
-                   CheckSameVE(TE.get());
-          });
-      if (I != VectorizableTree.end()) {
-        VE = I->get();
-        IsSameVE = true;
+    if (!IsSameVE) {
+      auto It = MultiNodeScalars.find(S.OpValue);
+      if (It != MultiNodeScalars.end()) {
+        auto *I = find_if(It->getSecond(), [&](const TreeEntry *TE) {
+          return TE != VE && CheckSameVE(TE);
+        });
+        if (I != It->getSecond().end()) {
+          VE = *I;
+          IsSameVE = true;
+        }
       }
     }
     if (IsSameVE) {