Update the code based on comments

Author: cxy-1993

llvm/include/llvm/ADT/EquivalenceClasses.h

@@ -17,6 +17,7 @@
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/Allocator.h"
 #include <cassert>
@@ -220,13 +221,18 @@ template <class ElemTy> class EquivalenceClasses {
     return *ECV;
   }
 
-  /// erase - Erase a value from the union/find set, return if erase succeed.
+  /// erase - Erase a value from the union/find set, return "true" if erase
+  /// succeeded.
   bool erase(const ElemTy &V) {
     if (!TheMapping.contains(V))
       return false;
     const ECValue *Cur = TheMapping[V];
     const ECValue *Next = Cur->getNext();
     if (Cur->isLeader()) {
+      // If the current element is the leader and has a successor element,
+      // update the successor element's 'Leader' field to be the last element,
+      // set the successor element's stolen bit, and set the 'Leader' field of
+      // all other elements in same class to be the successor element.
       if (Next) {
         Next->Leader = Cur->Leader;
         Next->Next = (const ECValue *)((intptr_t)Next->Next | (intptr_t)1);
@@ -242,21 +248,26 @@ template <class ElemTy> class EquivalenceClasses {
         Pre = Pre->getNext();
       }
       if (!Next) {
+        // If the current element is the last element(not leader), set the
+        // successor of the current element's predecessor to null, and set
+        // the 'Leader' field of the class leader to the predecessor element.
         Pre->Next = nullptr;
         Leader->Leader = Pre;
       } else {
+        // If the current element is in the middle of class, then simply
+        // connect the predecessor element and the successor element.
         Pre->Next =
             (const ECValue *)((intptr_t)Next | (intptr_t)Pre->isLeader());
         Next->Leader = Pre;
       }
     }
+
+    // Update 'TheMapping' and 'Members'.
+    assert(TheMapping.contains(V) && "Can't find input in TheMapping!");
     TheMapping.erase(V);
-    for (auto I = Members.begin(); I != Members.end(); I++) {
-      if (*I == Cur) {
-        Members.erase(I);
-        break;
-      }
-    }
+    auto I = llvm::find(Members, Cur);
+    assert(I != Members.end() && "Can't find input in members!");
+    Members.erase(I);
     return true;
   }