Improve and simplify removal of unreachable code

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index c058b0df44a44d3cbdf465f76752e4b76f53b7fb..c1f3d7566704f4ed19d1c89cc8dbca8551a5701a 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -997,10 +997,8 @@ LInstruction* LChunkBuilder::DoBranch(HBranch* instr) {
   if (value->EmitAtUses()) {
     ASSERT(value->IsConstant());
     ASSERT(!value->representation().IsDouble());
-    HBasicBlock* successor = HConstant::cast(value)->BooleanValue()
-        ? instr->FirstSuccessor()
-        : instr->SecondSuccessor();
-    return new(zone()) LGoto(successor->block_id());
+    return ElideControlInstruction(instr,
+                                   HConstant::cast(value)->BooleanValue());
   }
 
   LBranch* result = new(zone()) LBranch(UseRegister(value));
@@ -1637,6 +1635,13 @@ LInstruction* LChunkBuilder::DoCompareNumericAndBranch(
 
 LInstruction* LChunkBuilder::DoCompareObjectEqAndBranch(
     HCompareObjectEqAndBranch* instr) {
+  if (instr->left()->IsConstant() && instr->right()->IsConstant()) {
+    bool comparison_result =
+        HConstant::cast(instr->left())->SameConstantObject(
+            HConstant::cast(instr->right()));
+    return ElideControlInstruction(instr, comparison_result);
+  }
+
   LOperand* left = UseRegisterAtStart(instr->left());
   LOperand* right = UseRegisterOrConstantAtStart(instr->right());
   return new(zone()) LCmpObjectEqAndBranch(left, right);