diff --git a/mlir/lib/IR/AttributeDetail.h b/mlir/lib/IR/AttributeDetail.h
--- a/mlir/lib/IR/AttributeDetail.h
+++ b/mlir/lib/IR/AttributeDetail.h
@@ -193,8 +193,11 @@
   ArrayRef<char> data;
 
   /// The values used to denote a boolean splat value.
-  static constexpr char kSplatTrue = ~0;
-  static constexpr char kSplatFalse = 0;
+  // This is not using constexpr declaration due to compilation failure
+  // encountered with MSVC where it would inline these values, which makes it
+  // unsafe to refer by reference in KeyTy.
+  static const char kSplatTrue;
+  static const char kSplatFalse;
 };
 
 /// An attribute representing a reference to a dense vector or tensor object
diff --git a/mlir/lib/IR/BuiltinAttributes.cpp b/mlir/lib/IR/BuiltinAttributes.cpp
--- a/mlir/lib/IR/BuiltinAttributes.cpp
+++ b/mlir/lib/IR/BuiltinAttributes.cpp
@@ -438,6 +438,9 @@
 // DenseElementsAttr Utilities
 //===----------------------------------------------------------------------===//
 
+const char DenseIntOrFPElementsAttrStorage::kSplatTrue = ~0;
+const char DenseIntOrFPElementsAttrStorage::kSplatFalse = 0;
+
 /// Get the bitwidth of a dense element type within the buffer.
 /// DenseElementsAttr requires bitwidths greater than 1 to be aligned by 8.
 static size_t getDenseElementStorageWidth(size_t origWidth) {
diff --git a/mlir/unittests/IR/AttributeTest.cpp b/mlir/unittests/IR/AttributeTest.cpp
--- a/mlir/unittests/IR/AttributeTest.cpp
+++ b/mlir/unittests/IR/AttributeTest.cpp
@@ -74,6 +74,20 @@
   EXPECT_EQ(trueSplat, trueSplatFromRaw);
 }
 
+TEST(DenseSplatTest, BoolSplatSmall) {
+  MLIRContext context;
+  Builder builder(&context);
+
+  // Check that splats that don't fill entire byte are handled properly.
+  auto tensorType = RankedTensorType::get({4}, builder.getI1Type());
+  std::vector<char> data{0b00001111};
+  auto trueSplatFromRaw =
+      DenseIntOrFPElementsAttr::getFromRawBuffer(tensorType, data);
+  EXPECT_TRUE(trueSplatFromRaw.isSplat());
+  DenseElementsAttr trueSplat = DenseElementsAttr::get(tensorType, true);
+  EXPECT_EQ(trueSplat, trueSplatFromRaw);
+}
+
 TEST(DenseSplatTest, LargeBoolSplat) {
   constexpr int64_t boolCount = 56;