[EVM] Add merge identical bb pass to opt pipeline

Author: akiramenai

llvm/lib/Target/EVM/EVMTargetMachine.cpp

@@ -26,6 +26,7 @@
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Passes/PassBuilder.h"
 #include "llvm/Transforms/IPO/GlobalDCE.h"
+#include "llvm/Transforms/Scalar/MergeIdenticalBB.h"
 #include "llvm/Transforms/Utils.h"
 
 using namespace llvm;
@@ -115,6 +116,11 @@ void EVMTargetMachine::registerPassBuilderCallbacks(PassBuilder &PB) {
         PM.addPass(GlobalDCEPass());
         PM.addPass(createModuleToFunctionPassAdaptor(EVMAllocaHoistingPass()));
       });
+  PB.registerScalarOptimizerLateEPCallback(
+      [](FunctionPassManager &PM, OptimizationLevel Level) {
+        if (Level.getSizeLevel() || Level.getSpeedupLevel() > 1)
+          PM.addPass(MergeIdenticalBBPass());
+      });
 }
 
 namespace {