[Autobackout][FuncReg]Revert of change: ad59a84

 Add return instruction to functions without it

LLVM does not legally require a return instruction in a function.
However, return is needed by IGC BE to properly generate return code for control flow.
This change will add a return (if it does not exist) as the last instruction of the function.

Author: dlei6g

IGC/AdaptorCommon/LegalizeFunctionSignatures.cpp

@@ -80,8 +80,6 @@ bool LegalizeFunctionSignatures::runOnModule(Module& M)
 {
     auto pMdUtils = getAnalysis<MetaDataUtilsWrapper>().getMetaDataUtils();
 
-    // Add an unreachable return for functions without the return instruction
-    FixNoReturn(M);
     // Creates a new function declaration with modified signature
     FixFunctionSignatures(M);
     // Transforms all callers of the old function to the new function
@@ -667,34 +665,3 @@ void LegalizeFunctionSignatures::FixCallInstruction(Module& M, CallInst* callIns
         callInst->eraseFromParent();
     }
 }
-
-void LegalizeFunctionSignatures::FixNoReturn(Module& M)
-{
-    for (auto& FI : M)
-    {
-        if (!FI.empty())
-        {
-            // Search each BB for the ReturnInst
-            BasicBlock* lastBB = nullptr;
-            bool hasRetInst = false;
-            for (auto& BB : FI)
-            {
-                if (isa<ReturnInst>(BB.getTerminator()))
-                {
-                    hasRetInst = true;
-                    break;
-                }
-                lastBB = &BB;
-            }
-            // Insert an unreachable ReturnInst in the last BB
-            if (!hasRetInst)
-            {
-                IGCLLVM::IRBuilder<> builder(lastBB);
-                ReturnInst* dummyRet = FI.getReturnType()->isVoidTy() ?
-                    builder.CreateRetVoid() :
-                    builder.CreateRet(UndefValue::get(FI.getReturnType()));
-                dummyRet->moveAfter(lastBB->getTerminator());
-            }
-        }
-    }
-}

IGC/AdaptorCommon/LegalizeFunctionSignatures.h

@@ -40,7 +40,6 @@ class LegalizeFunctionSignatures : public llvm::ModulePass
     void FixFunctionBody(llvm::Module& M);
     void FixFunctionUsers(llvm::Module& M);
     void FixCallInstruction(llvm::Module& M, llvm::CallInst* callInst);
-    void FixNoReturn(llvm::Module& M);
 
     virtual llvm::StringRef getPassName() const
     {