[EarlyCSE] Cleanup deadcode. [NFCI]

[asbirlea]

Summary

Cleanup nop assignments.

[davide]

LGTM

llvm/trunk/lib/Transforms/Scalar/EarlyCSE.cpp

bool EarlyCSE::run() {
   bool Changed = false;
 
   // Process the root node.
   nodesToProcess.push_back(new StackNode(
       AvailableValues, AvailableLoads, AvailableInvariants, AvailableCalls,
       CurrentGeneration, DT.getRootNode(),
       DT.getRootNode()->begin(), DT.getRootNode()->end()));
 
-  // Save the current generation.
-  unsigned LiveOutGeneration = CurrentGeneration;
+  assert(!CurrentGeneration && "Create a new EarlyCSE instance to rerun it.");
 
   // Process the stack.
   while (!nodesToProcess.empty()) {
     // Grab the first item off the stack. Set the current generation, remove
     // the node from the stack, and process it.
     StackNode *NodeToProcess = nodesToProcess.back();
 
     // Initialize class members.
while (!nodesToProcess.empty()) {
     } else {
       // It has been processed, and there are no more children to process,
       // so delete it and pop it off the stack.
       delete NodeToProcess;
       nodesToProcess.pop_back();
     }
   } // while (!nodes...)
 
-  // Reset the current generation.
-  CurrentGeneration = LiveOutGeneration;
-
   return Changed;
 }
 
 PreservedAnalyses EarlyCSEPass::run(Function &F,
                                     FunctionAnalysisManager &AM) {
   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
   auto &TTI = AM.getResult<TargetIRAnalysis>(F);
   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);