[mlir][spirv] Simplify CompositeType::getNumElements. NFC. (#160202)

Use a type switch to simplify the implementation.

Author: kuhar

mlir/lib/Dialect/SPIRV/IR/SPIRVTypes.cpp

@@ -203,25 +203,13 @@ Type CompositeType::getElementType(unsigned index) const {
 }
 
 unsigned CompositeType::getNumElements() const {
-  if (auto arrayType = llvm::dyn_cast<ArrayType>(*this))
-    return arrayType.getNumElements();
-  if (auto matrixType = llvm::dyn_cast<MatrixType>(*this))
-    return matrixType.getNumColumns();
-  if (auto structType = llvm::dyn_cast<StructType>(*this))
-    return structType.getNumElements();
-  if (auto vectorType = llvm::dyn_cast<VectorType>(*this))
-    return vectorType.getNumElements();
-  if (auto tensorArmType = dyn_cast<TensorArmType>(*this))
-    return tensorArmType.getNumElements();
-  if (llvm::isa<CooperativeMatrixType>(*this)) {
-    llvm_unreachable(
-        "invalid to query number of elements of spirv Cooperative Matrix type");
-  }
-  if (llvm::isa<RuntimeArrayType>(*this)) {
-    llvm_unreachable(
-        "invalid to query number of elements of spirv::RuntimeArray type");
-  }
-  llvm_unreachable("invalid composite type");
+  return TypeSwitch<SPIRVType, unsigned>(*this)
+      .Case<ArrayType, StructType, TensorArmType, VectorType>(
+          [](auto type) { return type.getNumElements(); })
+      .Case<MatrixType>([](MatrixType type) { return type.getNumColumns(); })
+      .Default([](SPIRVType) -> unsigned {
+        llvm_unreachable("Invalid type for number of elements query");
+      });
 }
 
 bool CompositeType::hasCompileTimeKnownNumElements() const {