[IR] Change the default value of InstertElement to poison (1/4)

This patch is for fixing potential insertElement-related bugs like D93818.
```
V = UndefValue::get(VecTy);
for(...)
  V = Builder.CreateInsertElementy(V, Elt, Idx);
=>
V = PoisonValue::get(VecTy);
for(...)
  V = Builder.CreateInsertElementy(V, Elt, Idx);
```
Like above, this patch changes the placeholder V to poison.
The patch will be separated into several commits.

Reviewed By: aqjune

Differential Revision: https://reviews.llvm.org/D110311

Author: hyeongyukim

llvm/include/llvm/IR/IRBuilder.h

@@ -2452,6 +2452,16 @@ class IRBuilderBase {
     return CreateExtractElement(Vec, getInt64(Idx), Name);
   }
 
+  Value *CreateInsertElement(Type *VecTy, Value *NewElt, Value *Idx,
+                             const Twine &Name = "") {
+    return CreateInsertElement(PoisonValue::get(VecTy), NewElt, Idx, Name);
+  }
+
+  Value *CreateInsertElement(Type *VecTy, Value *NewElt, uint64_t Idx,
+                             const Twine &Name = "") {
+    return CreateInsertElement(PoisonValue::get(VecTy), NewElt, Idx, Name);
+  }
+
   Value *CreateInsertElement(Value *Vec, Value *NewElt, Value *Idx,
                              const Twine &Name = "") {
     if (auto *VC = dyn_cast<Constant>(Vec))

llvm/lib/IR/AutoUpgrade.cpp

@@ -2417,7 +2417,7 @@ void llvm::UpgradeIntrinsicCall(CallInst *CI, Function *NewFn) {
                                           EltTy->getPointerTo());
       Value *Load = Builder.CreateLoad(EltTy, Cast);
       Type *I32Ty = Type::getInt32Ty(C);
-      Rep = UndefValue::get(VecTy);
+      Rep = PoisonValue::get(VecTy);
       for (unsigned I = 0; I < EltNum; ++I)
         Rep = Builder.CreateInsertElement(Rep, Load,
                                           ConstantInt::get(I32Ty, I));

llvm/lib/Target/NVPTX/NVPTXGenericToNVVM.cpp

@@ -212,7 +212,7 @@ Value *GenericToNVVM::remapConstantVectorOrConstantAggregate(
   // If any of the elements has been  modified, construct the equivalent
   // vector or aggregate value with a set instructions and the converted
   // elements.
-  Value *NewValue = UndefValue::get(C->getType());
+  Value *NewValue = PoisonValue::get(C->getType());
   if (isa<ConstantVector>(C)) {
     for (unsigned i = 0; i < NumOperands; ++i) {
       Value *Idx = ConstantInt::get(Type::getInt32Ty(M->getContext()), i);

llvm/unittests/IR/IRBuilderTest.cpp

@@ -878,8 +878,7 @@ TEST_F(IRBuilderTest, InsertExtractElement) {
   auto VecTy = FixedVectorType::get(Builder.getInt64Ty(), 4);
   auto Elt1 = Builder.getInt64(-1);
   auto Elt2 = Builder.getInt64(-2);
-  Value *Vec = UndefValue::get(VecTy);
-  Vec = Builder.CreateInsertElement(Vec, Elt1, Builder.getInt8(1));
+  Value *Vec = Builder.CreateInsertElement(VecTy, Elt1, Builder.getInt8(1));
   Vec = Builder.CreateInsertElement(Vec, Elt2, 2);
   auto X1 = Builder.CreateExtractElement(Vec, 1);
   auto X2 = Builder.CreateExtractElement(Vec, Builder.getInt32(2));

llvm/unittests/IR/PatternMatch.cpp

@@ -940,8 +940,7 @@ TEST_F(PatternMatchTest, VectorOps) {
   VecElemIdxs.push_back(ConstantInt::get(i32, 2));
   auto *IdxVec = ConstantVector::get(VecElemIdxs);
 
-  Value *UndefVec = UndefValue::get(VecTy);
-  Value *VI1 = IRB.CreateInsertElement(UndefVec, IRB.getInt8(1), (uint64_t)0);
+  Value *VI1 = IRB.CreateInsertElement(VecTy, IRB.getInt8(1), (uint64_t)0);
   Value *VI2 = IRB.CreateInsertElement(VI1, Val2, Val);
   Value *VI3 = IRB.CreateInsertElement(VI1, Val2, (uint64_t)1);
   Value *VI4 = IRB.CreateInsertElement(VI1, IRB.getInt8(2), Val);