[IRBuilder] A method for creating a vector from scalar values

[chfast]

Summary

IRBuilder::CreateVectorPack method takes an array of values of the same scalar type and packs them into a vector with series of instertelement instructions.

[sanjoy]

LGTM with one minor comment inline.

include/llvm/IR/IRBuilder.h

1617

Mild preference: assert(!Elts.empty() ....

[chfast]

Thanks for the review.
Is the name "VectorPack" ok?

[sanjoy]

In D9372#196655, @chfast wrote:

Thanks for the review.
Is the name "VectorPack" ok?

I was initially going to suggest CreateVectorLiteral but what you're creating need not be a literal so that is misleading. So I'm fine with CreateVectorPack, but I suppose you could wait a little bit to see if someone else has a better idea.

include/llvm/IR/IRBuilder.h

Value *CreateVectorSplat(unsigned NumElts, Value *V, const Twine &Name = "") {
     V = CreateInsertElement(Undef, V, ConstantInt::get(I32Ty, 0),
                             Name + ".splatinsert");
 
     // Shuffle the value across the desired number of elements.
     Value *Zeros = ConstantAggregateZero::get(VectorType::get(I32Ty, NumElts));
     return CreateShuffleVector(V, Undef, Zeros, Name + ".splat");
   }
 
+  /// \brief Create a vector from scalar values.
+  ///
+  /// Returns a vector value with elements \p Elts inserted into it.
+  /// All elements values must have the same scalar type.
+  Value *CreateVectorPack(ArrayRef<Value *> Elts, const Twine &Name = "") {
+    assert(Elts.size() > 0 && "Cannot pack an empty vector");
+    auto *VectorTy = VectorType::get(Elts.front()->getType(), Elts.size());
+    Value *Vec = UndefValue::get(VectorTy);
+    for (size_t i = 0; i < Elts.size(); ++i)
+      Vec = CreateInsertElement(Vec, Elts[i], i, Name + ".pack");
+    return Vec;
+  }
+
   /// \brief Return a value that has been extracted from a larger integer type.
   Value *CreateExtractInteger(const DataLayout &DL, Value *From,
                               IntegerType *ExtractedTy, uint64_t Offset,
                               const Twine &Name) {
     IntegerType *IntTy = cast<IntegerType>(From->getType());
     assert(DL.getTypeStoreSize(ExtractedTy) + Offset <=
                DL.getTypeStoreSize(IntTy) &&
            "Element extends past full value");

unittests/IR/IRBuilderTest.cpp

TEST_F(IRBuilderTest, InsertExtractElement) {
   Vec = Builder.CreateInsertElement(Vec, Elt1, Builder.getInt8(1));
   Vec = Builder.CreateInsertElement(Vec, Elt2, 2);
   auto X1 = Builder.CreateExtractElement(Vec, 1);
   auto X2 = Builder.CreateExtractElement(Vec, Builder.getInt32(2));
   EXPECT_EQ(Elt1, X1);
   EXPECT_EQ(Elt2, X2);
 }
 
+TEST_F(IRBuilderTest, VectorPack) {
+  IRBuilder<> Builder(BB);
+
+  Value *Elts[] = {Builder.getInt16(-1),
+                   Builder.getInt16(-2),
+                   Builder.getInt16(-3)};
+  auto *Vec = Builder.CreateVectorPack(Elts, "v");
+  EXPECT_EQ(VectorType::get(Builder.getInt16Ty(), 3), Vec->getType());
+  auto *Elt2 = Builder.CreateExtractElement(Vec, 2);
+  EXPECT_EQ(Builder.getInt16(-3), Elt2);
+}
+
 
 }