Remove deadcode, null checks, use llvm:cast

Addresses issues found by Coverity.

Author: fda0

IGC/Compiler/CISACodeGen/CodeSinking.hpp

@@ -157,6 +157,8 @@ namespace IGC {
             Candidate(const Candidate& Other)
                 : Instructions(Other.Instructions), TgtBB(Other.TgtBB), Worthiness(Other.Worthiness), UndoPos(Other.UndoPos) {}
 
+            Candidate& operator=(const Candidate&) = delete;
+
             InstrVec Instructions;
 
             BasicBlock *TgtBB;

IGC/Compiler/CISACodeGen/IGCVectorizer.h

@@ -76,6 +76,8 @@ class IGCVectorizer : public llvm::FunctionPass {
     public:
     llvm::StringRef getPassName() const override { return "IGCVectorizer"; }
     virtual ~IGCVectorizer() { ScalarToVector.clear(); }
+    IGCVectorizer(const IGCVectorizer&) = delete;
+    IGCVectorizer& operator=(const IGCVectorizer&) = delete;
     virtual bool runOnFunction(llvm::Function &F) override;
     virtual void getAnalysisUsage(llvm::AnalysisUsage &AU) const override {
         AU.addRequired<CodeGenContextWrapper>();

IGC/Compiler/CISACodeGen/LoopCountAnalysis.cpp

@@ -499,21 +499,15 @@ void LoopCountAnalysis::processLoop(Loop* L) {
         }
 
         if (IGC_IS_FLAG_ENABLED(EnableKernelCostDebug)) {
-            if (I0) {
-                dbgs() << " init value: ";
-                I0->print(output);
-                dbgs() << "\n";
-            }
-            if (In) {
-                dbgs() << " end value: ";
-                In->print(output);
-                dbgs() << "\n";
-            }
-            if (step) {
-                dbgs() << " step value: ";
-                step->print(output);
-                dbgs() << "\n";
-            }
+            dbgs() << " init value: ";
+            I0->print(output);
+            dbgs() << "\n";
+            dbgs() << " end value: ";
+            In->print(output);
+            dbgs() << "\n";
+            dbgs() << " step value: ";
+            step->print(output);
+            dbgs() << "\n";
         }
 
         ConstantInt* addValue = nullptr;

IGC/Compiler/Optimizer/OpenCLPasses/SubGroupReductionPattern/SubGroupReductionPattern.cpp

@@ -394,7 +394,7 @@ void SubGroupReductionPattern::matchVectorShufflePattern(GenIntrinsicInst &Shuff
 
     for (auto *User : InputValue->users())
     {
-        Instruction *Op = dyn_cast<Instruction>(User);
+        Instruction *Op = cast<Instruction>(User);
 
         if (match(Op, m_c_BinOp(m_Specific(InputValue), Pattern1)) || match(Op, m_c_BinOp(m_Specific(InputValue), Pattern2)))
         {