[IR] Add IRBuilderBase::CreateVectorSplat(ElementCount EC) variant

As discussed on D81500, this adds a more general ElementCount variant of the build helper and converts the (non-scalable) unsigned NumElts variant to use it internally.

llvm/include/llvm/IR/IRBuilder.h

@@ -2484,6 +2484,10 @@ public:
   /// NumElts elements.
   Value *CreateVectorSplat(unsigned NumElts, Value *V, const Twine &Name = "");
 
+  /// Return a vector value that contains \arg V broadcasted to \p
+  /// EC elements.
+  Value *CreateVectorSplat(ElementCount EC, Value *V, const Twine &Name = "");
+
   /// Return a value that has been extracted from a larger integer type.
   Value *CreateExtractInteger(const DataLayout &DL, Value *From,
                               IntegerType *ExtractedTy, uint64_t Offset,

llvm/lib/IR/IRBuilder.cpp

@@ -996,17 +996,22 @@ Value *IRBuilderBase::CreateStripInvariantGroup(Value *Ptr) {
 
 Value *IRBuilderBase::CreateVectorSplat(unsigned NumElts, Value *V,
                                         const Twine &Name) {
-  assert(NumElts > 0 && "Cannot splat to an empty vector!");
+  ElementCount EC(NumElts, false);
+  return CreateVectorSplat(EC, V, Name);
+}
+
+Value *IRBuilderBase::CreateVectorSplat(ElementCount EC, Value *V,
+                                        const Twine &Name) {
+  assert(EC.Min > 0 && "Cannot splat to an empty vector!");
 
   // First insert it into an undef vector so we can shuffle it.
   Type *I32Ty = getInt32Ty();
-  Value *Undef = UndefValue::get(FixedVectorType::get(V->getType(), NumElts));
+  Value *Undef = UndefValue::get(VectorType::get(V->getType(), EC));
   V = CreateInsertElement(Undef, V, ConstantInt::get(I32Ty, 0),
                           Name + ".splatinsert");
 
   // Shuffle the value across the desired number of elements.
-  Value *Zeros =
-      ConstantAggregateZero::get(FixedVectorType::get(I32Ty, NumElts));
+  Value *Zeros = ConstantAggregateZero::get(VectorType::get(I32Ty, EC));
   return CreateShuffleVector(V, Undef, Zeros, Name + ".splat");
 }
 

llvm/unittests/Analysis/VectorUtilsTest.cpp

@@ -93,6 +93,9 @@ TEST_F(BasicTest, isSplat) {
   Value *SplatC = IRB.CreateVectorSplat(5, ScalarC);
   EXPECT_TRUE(isSplatValue(SplatC));
 
+  Value *SplatC_SVE = IRB.CreateVectorSplat(ElementCount(5, true), ScalarC);
+  EXPECT_TRUE(isSplatValue(SplatC_SVE));
+
   // FIXME: Constant splat analysis does not allow undef elements.
   Constant *SplatWithUndefC = ConstantVector::get({ScalarC, UndefScalar});
   EXPECT_FALSE(isSplatValue(SplatWithUndefC));