IntEqClasses: Let join() return the new leader

The new leader is known anyway so we can return it for some micro
optimization in code where it is easy to pass along the result to the
next join().

llvm-svn: 257130

2 files changed, 7 insertions, 5 deletions

diff --git a/llvm/include/llvm/ADT/IntEqClasses.h b/llvm/include/llvm/ADT/IntEqClasses.h
index 8e75c48e376..0baee2f11a7 100644
--- a/llvm/include/llvm/ADT/IntEqClasses.h
+++ b/llvm/include/llvm/ADT/IntEqClasses.h
@@ -53,10 +53,10 @@ public:
     NumClasses = 0;
   }
 
-  /// join - Join the equivalence classes of a and b. After joining classes,
-  /// findLeader(a) == findLeader(b).
-  /// This requires an uncompressed map.
-  void join(unsigned a, unsigned b);
+  /// Join the equivalence classes of a and b. After joining classes,
+  /// findLeader(a) == findLeader(b). This requires an uncompressed map.
+  /// Returns the new leader.
+  unsigned join(unsigned a, unsigned b);
 
   /// findLeader - Compute the leader of a's equivalence class. This is the
   /// smallest member of the class.
diff --git a/llvm/lib/Support/IntEqClasses.cpp b/llvm/lib/Support/IntEqClasses.cpp
index 11344956e4c..ff213570807 100644
--- a/llvm/lib/Support/IntEqClasses.cpp
+++ b/llvm/lib/Support/IntEqClasses.cpp
@@ -29,7 +29,7 @@ void IntEqClasses::grow(unsigned N) {
     EC.push_back(EC.size());
 }
 
-void IntEqClasses::join(unsigned a, unsigned b) {
+unsigned IntEqClasses::join(unsigned a, unsigned b) {
   assert(NumClasses == 0 && "join() called after compress().");
   unsigned eca = EC[a];
   unsigned ecb = EC[b];
@@ -41,6 +41,8 @@ void IntEqClasses::join(unsigned a, unsigned b) {
       EC[b] = eca, b = ecb, ecb = EC[b];
     else
       EC[a] = ecb, a = eca, eca = EC[a];
+
+  return eca;
 }
 
 unsigned IntEqClasses::findLeader(unsigned a) const {