[IR] Add the constructor of ShuffleVector for one-input-vector.

[hyeongyukim]

Summary

One of the two inputs of the Shufflevector is often a placeholder.
Previously, there were cases where the placeholder was undef, and there were cases where it was poison.
I added these constructors to create a placeholder consistently.

Changing to use the newly added constructor will be written in a separate patch.

[spatel]

LGTM - thanks!

llvm/include/llvm/IR/Instructions.h

2021

Cutting the "e" off of "Before" might have been a hack to make this fit in 80-columns for the original code, but it would be nice to spell it correctly now in all of these declarations. :)

llvm/lib/IR/Instructions.cpp

1910

We call this a "unary shuffle" in the IRBuilder code comments, so "createOperandForUnaryShuffle" might make it clearer that this is the same functionality for the raw constructors.

[hyeongyukim]

rebase and change function name.

llvm/include/llvm/IR/Instructions.h

 
 protected:
   // Note: Instruction needs to be a friend here to call cloneImpl.
   friend class Instruction;
 
   ShuffleVectorInst *cloneImpl() const;
 
 public:
+  ShuffleVectorInst(Value *V1, Value *Mask, const Twine &NameStr = "",
+                    Instruction *InsertBefor = nullptr);
+  ShuffleVectorInst(Value *V1, Value *Mask, const Twine &NameStr,
+                    BasicBlock *InsertAtEnd);
+  ShuffleVectorInst(Value *V1, ArrayRef<int> Mask, const Twine &NameStr = "",
+                    Instruction *InsertBefor = nullptr);
+  ShuffleVectorInst(Value *V1, ArrayRef<int> Mask, const Twine &NameStr,
+                    BasicBlock *InsertAtEnd);
   ShuffleVectorInst(Value *V1, Value *V2, Value *Mask,
                     const Twine &NameStr = "",
                     Instruction *InsertBefor = nullptr);
   ShuffleVectorInst(Value *V1, Value *V2, Value *Mask,
                     const Twine &NameStr, BasicBlock *InsertAtEnd);
   ShuffleVectorInst(Value *V1, Value *V2, ArrayRef<int> Mask,
                     const Twine &NameStr = "",
                     Instruction *InsertBefor = nullptr);

llvm/lib/IR/Instructions.cpp

if (!Index->getType()->isIntegerTy())
     return false;  // Third operand of insertelement must be i32.
   return true;
 }
 
 //===----------------------------------------------------------------------===//
 //                      ShuffleVectorInst Implementation
 //===----------------------------------------------------------------------===//
 
+static Value *createPlaceholderOfShuffleVector(Value *V) {
+  assert(V && "Cannot create placeholder of nullptr V");
+  return PoisonValue::get(V->getType());
+}
+
+ShuffleVectorInst::ShuffleVectorInst(Value *V1, Value *Mask, const Twine &Name,
+                                     Instruction *InsertBefore)
+    : ShuffleVectorInst(V1, createPlaceholderOfShuffleVector(V1), Mask, Name,
+                        InsertBefore) {}
+
+ShuffleVectorInst::ShuffleVectorInst(Value *V1, Value *Mask, const Twine &Name,
+                                     BasicBlock *InsertAtEnd)
+    : ShuffleVectorInst(V1, createPlaceholderOfShuffleVector(V1), Mask, Name,
+                        InsertAtEnd) {}
+
+ShuffleVectorInst::ShuffleVectorInst(Value *V1, ArrayRef<int> Mask,
+                                     const Twine &Name,
+                                     Instruction *InsertBefore)
+    : ShuffleVectorInst(V1, createPlaceholderOfShuffleVector(V1), Mask, Name,
+                        InsertBefore) {}
+
+ShuffleVectorInst::ShuffleVectorInst(Value *V1, ArrayRef<int> Mask,
+                                     const Twine &Name, BasicBlock *InsertAtEnd)
+    : ShuffleVectorInst(V1, createPlaceholderOfShuffleVector(V1), Mask, Name,
+                        InsertAtEnd) {}
+
 ShuffleVectorInst::ShuffleVectorInst(Value *V1, Value *V2, Value *Mask,
                                      const Twine &Name,
                                      Instruction *InsertBefore)
     : Instruction(
           VectorType::get(cast<VectorType>(V1->getType())->getElementType(),
                           cast<VectorType>(Mask->getType())->getElementCount()),
           ShuffleVector, OperandTraits<ShuffleVectorInst>::op_begin(this),
           OperandTraits<ShuffleVectorInst>::operands(this), InsertBefore) {