Various improvements suggested by river NFC.

[lattner]

This should be part of https://reviews.llvm.org/D125447, weird.

mlir/include/mlir/IR/BuiltinAttributes.td

def Builtin_DenseIntOrFPElementsAttr : Builtin_Attr<
   protected:
     friend DenseElementsAttr;
 
     /// Constructs a dense elements attribute from an array of raw APFloat
     /// values. Each APFloat value is expected to have the same bitwidth as the
     /// element type of 'type'. 'type' must be a vector or tensor with static
     /// shape.
     ///
-    /// If the `values` array only has a single element, then this  constructs
+    /// If the `values` array only has a single element, then this constructs
     /// splat of that value.
     static DenseElementsAttr getRaw(ShapedType type, size_t storageWidth,
                                     ArrayRef<APFloat> values);
 
     /// Constructs a dense elements attribute from an array of raw APInt values.
     /// Each APInt value is expected to have the same bitwidth as the element
     /// type of 'type'. 'type' must be a vector or tensor with static shape.
     ///
-    /// If the `values` array only has a single element, then this  constructs
+    /// If the `values` array only has a single element, then this constructs
     /// splat of that value.
     static DenseElementsAttr getRaw(ShapedType type, size_t storageWidth,
                                     ArrayRef<APInt> values);
 
     /// Get or create a new dense elements attribute instance with the given raw
     /// data buffer. 'type' must be a vector or tensor with static shape.
     ///
-    /// If the `values` array only has a single element, then this  constructs
+    /// If the `values` array only has a single element, then this constructs
     /// splat of that value.
     static DenseElementsAttr getRaw(ShapedType type, ArrayRef<char> data);
 
     /// Overload of the raw 'get' method that asserts that the given type is of
     /// complex type. This method is used to verify type invariants that the
     /// templatized 'get' method cannot.
     static DenseElementsAttr getRawComplex(ShapedType type, ArrayRef<char> data,
                                            int64_t dataEltSize, bool isInt,
let description = [{
     dense<["example1", "example2"]> : tensor<2x!foo.string>
     ```
   }];
   let parameters = (ins AttributeSelfTypeParameter<"", "ShapedType">:$type,
                         "ArrayRef<StringRef>":$value);
   let builders = [
     AttrBuilderWithInferredContext<(ins "ShapedType":$type,
                                         "ArrayRef<StringRef>":$values), [{
-      return $_get(type.getContext(), type, values, 
+      return $_get(type.getContext(), type, values,
                    /* isSplat */(values.size() == 1));
     }]>,
   ];
   let extraClassDeclaration = [{
     using DenseElementsAttr::empty;
     using DenseElementsAttr::getNumElements;
     using DenseElementsAttr::getElementType;
     using DenseElementsAttr::getValues;

mlir/lib/IR/BuiltinAttributes.cpp

DenseElementsAttr DenseElementsAttr::get(ShapedType type,
   if (!values.empty()) {
     bool isSplat = true;
     bool firstValue = values[0];
     for (int i = 0, e = values.size(); i != e; ++i) {
       isSplat &= values[i] == firstValue;
       setBit(buff.data(), i, values[i]);
     }
 
-    if (isSplat) { // special encoding for splat.
+    // Splat of bool is encoded as a byte with all-ones in it.
+    if (isSplat) {
       buff.resize(1);
       buff[0] = values[0] ? -1 : 0;
     }
   }
 
   return DenseIntOrFPElementsAttr::getRaw(type, buff);
 }