diff --git a/src/ast/function.cc b/src/ast/function.cc
index 8f8ab730cd..d921e893e5 100644
--- a/src/ast/function.cc
+++ b/src/ast/function.cc
@@ -38,7 +38,7 @@ Function::Function(const Source& source,
       decorations_(std::move(decorations)),
       return_type_decorations_(std::move(return_type_decorations)) {
   for (auto* param : params_) {
-    TINT_ASSERT(param);
+    TINT_ASSERT(param && param->is_const());
   }
   TINT_ASSERT(symbol_.IsValid());
   TINT_ASSERT(return_type_);
diff --git a/src/ast/function_test.cc b/src/ast/function_test.cc
index ccb9071fd9..a9bdf0e74b 100644
--- a/src/ast/function_test.cc
+++ b/src/ast/function_test.cc
@@ -26,7 +26,7 @@ using FunctionTest = TestHelper;
 
 TEST_F(FunctionTest, Creation) {
   VariableList params;
-  params.push_back(Var("var", ty.i32(), StorageClass::kNone));
+  params.push_back(Param("var", ty.i32()));
   auto* var = params[0];
 
   auto* f = Func("func", params, ty.void_(), StatementList{}, DecorationList{});
@@ -38,7 +38,7 @@ TEST_F(FunctionTest, Creation) {
 
 TEST_F(FunctionTest, Creation_WithSource) {
   VariableList params;
-  params.push_back(Var("var", ty.i32(), StorageClass::kNone));
+  params.push_back(Param("var", ty.i32()));
 
   auto* f = Func(Source{Source::Location{20, 2}}, "func", params, ty.void_(),
                  StatementList{}, DecorationList{});
@@ -71,7 +71,7 @@ TEST_F(FunctionTest, Assert_NullParam) {
       {
         ProgramBuilder b;
         VariableList params;
-        params.push_back(b.Var("var", b.ty.i32(), StorageClass::kNone));
+        params.push_back(b.Param("var", b.ty.i32()));
         params.push_back(nullptr);
 
         b.Func("f", params, b.ty.void_(), StatementList{}, DecorationList{});
@@ -79,6 +79,18 @@ TEST_F(FunctionTest, Assert_NullParam) {
       "internal compiler error");
 }
 
+TEST_F(FunctionTest, Assert_NonConstParam) {
+  EXPECT_FATAL_FAILURE(
+      {
+        ProgramBuilder b;
+        VariableList params;
+        params.push_back(b.Var("var", b.ty.i32(), ast::StorageClass::kNone));
+
+        b.Func("f", params, b.ty.void_(), StatementList{}, DecorationList{});
+      },
+      "internal compiler error");
+}
+
 TEST_F(FunctionTest, ToStr) {
   auto* f = Func("func", VariableList{}, ty.void_(),
                  StatementList{
@@ -112,7 +124,7 @@ WorkgroupDecoration{2 4 6}
 
 TEST_F(FunctionTest, ToStr_WithParams) {
   VariableList params;
-  params.push_back(Var("var", ty.i32(), StorageClass::kNone));
+  params.push_back(Param("var", ty.i32()));
 
   auto* f = Func("func", params, ty.void_(),
                  StatementList{
@@ -122,7 +134,7 @@ TEST_F(FunctionTest, ToStr_WithParams) {
 
   EXPECT_EQ(str(f), R"(Function func -> __void
 (
-  Variable{
+  VariableConst{
     var
     none
     __i32
@@ -142,8 +154,8 @@ TEST_F(FunctionTest, TypeName) {
 
 TEST_F(FunctionTest, TypeName_WithParams) {
   VariableList params;
-  params.push_back(Var("var1", ty.i32(), StorageClass::kNone));
-  params.push_back(Var("var2", ty.f32(), StorageClass::kNone));
+  params.push_back(Param("var1", ty.i32()));
+  params.push_back(Param("var2", ty.f32()));
 
   auto* f = Func("func", params, ty.void_(), StatementList{}, DecorationList{});
   EXPECT_EQ(f->type_name(), "__func__void__i32__f32");
diff --git a/src/program_builder.h b/src/program_builder.h
index ae197ccac4..6c728cc4b5 100644
--- a/src/program_builder.h
+++ b/src/program_builder.h
@@ -815,7 +815,7 @@ class ProgramBuilder {
   /// @param type the variable type
   /// @param constructor optional constructor expression
   /// @param decorations optional variable decorations
-  /// @returns a constant `ast::Variable` with the given name, storage and type
+  /// @returns a constant `ast::Variable` with the given name and type
   template <typename NAME>
   ast::Variable* Const(NAME&& name,
                        type::Type* type,
@@ -831,7 +831,7 @@ class ProgramBuilder {
   /// @param type the variable type
   /// @param constructor optional constructor expression
   /// @param decorations optional variable decorations
-  /// @returns a constant `ast::Variable` with the given name, storage and type
+  /// @returns a constant `ast::Variable` with the given name and type
   template <typename NAME>
   ast::Variable* Const(const Source& source,
                        NAME&& name,
@@ -843,6 +843,34 @@ class ProgramBuilder {
                                  constructor, decorations);
   }
 
+  /// @param name the parameter name
+  /// @param type the parameter type
+  /// @param decorations optional parameter decorations
+  /// @returns a constant `ast::Variable` with the given name and type
+  template <typename NAME>
+  ast::Variable* Param(NAME&& name,
+                       type::Type* type,
+                       ast::DecorationList decorations = {}) {
+    return create<ast::Variable>(Sym(std::forward<NAME>(name)),
+                                 ast::StorageClass::kNone, type, true, nullptr,
+                                 decorations);
+  }
+
+  /// @param source the parameter source
+  /// @param name the parameter name
+  /// @param type the parameter type
+  /// @param decorations optional parameter decorations
+  /// @returns a constant `ast::Variable` with the given name and type
+  template <typename NAME>
+  ast::Variable* Param(const Source& source,
+                       NAME&& name,
+                       type::Type* type,
+                       ast::DecorationList decorations = {}) {
+    return create<ast::Variable>(source, Sym(std::forward<NAME>(name)),
+                                 ast::StorageClass::kNone, type, true, nullptr,
+                                 decorations);
+  }
+
   /// @param args the arguments to pass to Var()
   /// @returns a `ast::Variable` constructed by calling Var() with the arguments
   /// of `args`, which is automatically registered as a global variable with the
diff --git a/src/resolver/entry_point_validation_test.cc b/src/resolver/entry_point_validation_test.cc
index 067186b51f..4b31d1a314 100644
--- a/src/resolver/entry_point_validation_test.cc
+++ b/src/resolver/entry_point_validation_test.cc
@@ -253,7 +253,7 @@ TEST_F(ResolverEntryPointValidationTest, ReturnType_Struct_DuplicateLocation) {
 TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Location) {
   // [[stage(fragment)]]
   // fn main([[location(0)]] param : f32) {}
-  auto* param = Const("param", ty.f32(), nullptr, {Location(0)});
+  auto* param = Param("param", ty.f32(), {Location(0)});
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -263,8 +263,8 @@ TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Location) {
 TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Builtin) {
   // [[stage(fragment)]]
   // fn main([[builtin(frag_depth)]] param : f32) {}
-  auto* param = Const("param", ty.vec4<f32>(), nullptr,
-                      {Builtin(ast::Builtin::kFragDepth)});
+  auto* param =
+      Param("param", ty.vec4<f32>(), {Builtin(ast::Builtin::kFragDepth)});
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -274,7 +274,7 @@ TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Builtin) {
 TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Missing) {
   // [[stage(fragment)]]
   // fn main(param : f32) {}
-  auto* param = Const(Source{{13, 43}}, "param", ty.vec4<f32>(), nullptr);
+  auto* param = Param(Source{{13, 43}}, "param", ty.vec4<f32>());
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -286,7 +286,7 @@ TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Missing) {
 TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Multiple) {
   // [[stage(fragment)]]
   // fn main([[location(0)]] [[builtin(vertex_index)]] param : u32) {}
-  auto* param = Const("param", ty.u32(), nullptr,
+  auto* param = Param("param", ty.u32(),
                       {Location(Source{{13, 43}}, 0),
                        Builtin(Source{{14, 52}}, ast::Builtin::kVertexIndex)});
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
@@ -303,7 +303,7 @@ TEST_F(ResolverEntryPointValidationTest, ParameterAttribute_Struct) {
   // [[stage(fragment)]]
   // fn main([[location(0)]] param : Input) {}
   auto* input = Structure("Input", {});
-  auto* param = Const("param", input, nullptr, {Location(Source{{13, 43}}, 0)});
+  auto* param = Param("param", input, {Location(Source{{13, 43}}, 0)});
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -324,7 +324,7 @@ TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_Valid) {
   auto* input = Structure(
       "Input", {Member("a", ty.f32(), {Location(0)}),
                 Member("b", ty.u32(), {Builtin(ast::Builtin::kSampleIndex)})});
-  auto* param = Const("param", input);
+  auto* param = Param("param", input);
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -343,7 +343,7 @@ TEST_F(ResolverEntryPointValidationTest,
       {Member("a", ty.f32(),
               {Location(Source{{13, 43}}, 0),
                Builtin(Source{{14, 52}}, ast::Builtin::kSampleIndex)})});
-  auto* param = Const("param", input);
+  auto* param = Param("param", input);
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -364,7 +364,7 @@ TEST_F(ResolverEntryPointValidationTest,
   auto* input = Structure(
       "Input", {Member(Source{{13, 43}}, "a", ty.f32(), {Location(0)}),
                 Member(Source{{14, 52}}, "b", ty.f32(), {})});
-  auto* param = Const("param", input);
+  auto* param = Param("param", input);
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -386,7 +386,7 @@ TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_NestedStruct) {
       "Inner", {Member(Source{{13, 43}}, "a", ty.f32(), {Location(0)})});
   auto* input =
       Structure("Input", {Member(Source{{14, 52}}, "a", inner, {Location(0)})});
-  auto* param = Const("param", input);
+  auto* param = Param("param", input);
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -408,7 +408,7 @@ TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_RuntimeArray) {
       "Input",
       {Member(Source{{13, 43}}, "a", ty.array<float>(), {Location(0)})},
       {create<ast::StructBlockDecoration>()});
-  auto* param = Const("param", input);
+  auto* param = Param("param", input);
   Func(Source{{12, 34}}, "main", {param}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -423,10 +423,10 @@ TEST_F(ResolverEntryPointValidationTest, Parameter_DuplicateBuiltins) {
   // [[stage(fragment)]]
   // fn main([[builtin(sample_index)]] param_a : u32,
   //         [[builtin(sample_index)]] param_b : u32) {}
-  auto* param_a = Const("param_a", ty.u32(), nullptr,
-                        {Builtin(ast::Builtin::kSampleIndex)});
-  auto* param_b = Const("param_b", ty.u32(), nullptr,
-                        {Builtin(ast::Builtin::kSampleIndex)});
+  auto* param_a =
+      Param("param_a", ty.u32(), {Builtin(ast::Builtin::kSampleIndex)});
+  auto* param_b =
+      Param("param_b", ty.u32(), {Builtin(ast::Builtin::kSampleIndex)});
   Func(Source{{12, 34}}, "main", {param_a, param_b}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -450,8 +450,8 @@ TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_DuplicateBuiltins) {
       "InputA", {Member("a", ty.u32(), {Builtin(ast::Builtin::kSampleIndex)})});
   auto* input_b = Structure(
       "InputB", {Member("a", ty.u32(), {Builtin(ast::Builtin::kSampleIndex)})});
-  auto* param_a = Const("param_a", input_a);
-  auto* param_b = Const("param_b", input_b);
+  auto* param_a = Param("param_a", input_a);
+  auto* param_b = Param("param_b", input_b);
   Func(Source{{12, 34}}, "main", {param_a, param_b}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -466,8 +466,8 @@ TEST_F(ResolverEntryPointValidationTest, Parameter_DuplicateLocation) {
   // [[stage(fragment)]]
   // fn main([[location(1)]] param_a : f32,
   //         [[location(1)]] param_b : f32) {}
-  auto* param_a = Const("param_a", ty.u32(), nullptr, {Location(1)});
-  auto* param_b = Const("param_b", ty.u32(), nullptr, {Location(1)});
+  auto* param_a = Param("param_a", ty.u32(), {Location(1)});
+  auto* param_b = Param("param_b", ty.u32(), {Location(1)});
   Func(Source{{12, 34}}, "main", {param_a, param_b}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
@@ -488,8 +488,8 @@ TEST_F(ResolverEntryPointValidationTest, Parameter_Struct_DuplicateLocation) {
   // fn main(param_a : InputA, param_b : InputB) {}
   auto* input_a = Structure("InputA", {Member("a", ty.f32(), {Location(1)})});
   auto* input_b = Structure("InputB", {Member("a", ty.f32(), {Location(1)})});
-  auto* param_a = Const("param_a", input_a);
-  auto* param_b = Const("param_b", input_b);
+  auto* param_a = Param("param_a", input_a);
+  auto* param_b = Param("param_b", input_b);
   Func(Source{{12, 34}}, "main", {param_a, param_b}, ty.void_(), {},
        {Stage(ast::PipelineStage::kFragment)});
 
diff --git a/src/resolver/function_validation_test.cc b/src/resolver/function_validation_test.cc
index 76ae8f54e1..daf14ad66b 100644
--- a/src/resolver/function_validation_test.cc
+++ b/src/resolver/function_validation_test.cc
@@ -248,7 +248,7 @@ TEST_F(ResolverFunctionValidationTest, FunctionVarInitWithParam) {
   //   var baz : f32 = bar;
   // }
 
-  auto* bar = Var("bar", ty.f32(), ast::StorageClass::kFunction);
+  auto* bar = Param("bar", ty.f32());
   auto* baz = Var("baz", ty.f32(), ast::StorageClass::kFunction, Expr("bar"));
 
   Func("foo", ast::VariableList{bar}, ty.void_(), ast::StatementList{Decl(baz)},
@@ -262,7 +262,7 @@ TEST_F(ResolverFunctionValidationTest, FunctionConstInitWithParam) {
   //   let baz : f32 = bar;
   // }
 
-  auto* bar = Var("bar", ty.f32(), ast::StorageClass::kFunction);
+  auto* bar = Param("bar", ty.f32());
   auto* baz = Const("baz", ty.f32(), Expr("bar"));
 
   Func("foo", ast::VariableList{bar}, ty.void_(), ast::StatementList{Decl(baz)},
diff --git a/src/resolver/struct_pipeline_stage_use_test.cc b/src/resolver/struct_pipeline_stage_use_test.cc
index 6804e47589..d4c615399f 100644
--- a/src/resolver/struct_pipeline_stage_use_test.cc
+++ b/src/resolver/struct_pipeline_stage_use_test.cc
@@ -42,7 +42,7 @@ TEST_F(ResolverPipelineStageUseTest, StructUsedAsNonEntryPointParam) {
   auto* s = Structure(
       "S", {Member("a", ty.f32(), {create<ast::LocationDecoration>(0)})});
 
-  Func("foo", {Const("param", s)}, ty.void_(), {}, {});
+  Func("foo", {Param("param", s)}, ty.void_(), {}, {});
 
   ASSERT_TRUE(r()->Resolve()) << r()->error();
 
@@ -68,7 +68,7 @@ TEST_F(ResolverPipelineStageUseTest, StructUsedAsVertexShaderParam) {
   auto* s = Structure(
       "S", {Member("a", ty.f32(), {create<ast::LocationDecoration>(0)})});
 
-  Func("main", {Const("param", s)}, ty.void_(), {},
+  Func("main", {Param("param", s)}, ty.void_(), {},
        {create<ast::StageDecoration>(ast::PipelineStage::kVertex)});
 
   ASSERT_TRUE(r()->Resolve()) << r()->error();
@@ -99,7 +99,7 @@ TEST_F(ResolverPipelineStageUseTest, StructUsedAsFragmentShaderParam) {
   auto* s = Structure(
       "S", {Member("a", ty.f32(), {create<ast::LocationDecoration>(0)})});
 
-  Func("main", {Const("param", s)}, ty.void_(), {},
+  Func("main", {Param("param", s)}, ty.void_(), {},
        {create<ast::StageDecoration>(ast::PipelineStage::kFragment)});
 
   ASSERT_TRUE(r()->Resolve()) << r()->error();
@@ -132,7 +132,7 @@ TEST_F(ResolverPipelineStageUseTest, StructUsedAsComputeShaderParam) {
                                    {create<ast::BuiltinDecoration>(
                                        ast::Builtin::kLocalInvocationIndex)})});
 
-  Func("main", {Const("param", s)}, ty.void_(), {},
+  Func("main", {Param("param", s)}, ty.void_(), {},
        {create<ast::StageDecoration>(ast::PipelineStage::kCompute)});
 
   ASSERT_TRUE(r()->Resolve()) << r()->error();
@@ -148,10 +148,10 @@ TEST_F(ResolverPipelineStageUseTest, StructUsedMultipleStages) {
   auto* s = Structure(
       "S", {Member("a", ty.f32(), {create<ast::LocationDecoration>(0)})});
 
-  Func("vert_main", {Const("param", s)}, s, {Return(Construct(s, Expr(0.f)))},
+  Func("vert_main", {Param("param", s)}, s, {Return(Construct(s, Expr(0.f)))},
        {create<ast::StageDecoration>(ast::PipelineStage::kVertex)});
 
-  Func("frag_main", {Const("param", s)}, ty.void_(), {},
+  Func("frag_main", {Param("param", s)}, ty.void_(), {},
        {create<ast::StageDecoration>(ast::PipelineStage::kFragment)});
 
   ASSERT_TRUE(r()->Resolve()) << r()->error();
@@ -170,7 +170,7 @@ TEST_F(ResolverPipelineStageUseTest, StructUsedAsShaderParamViaAlias) {
       "S", {Member("a", ty.f32(), {create<ast::LocationDecoration>(0)})});
   auto* s_alias = ty.alias("S_alias", s);
 
-  Func("main", {Const("param", s_alias)}, ty.void_(), {},
+  Func("main", {Param("param", s_alias)}, ty.void_(), {},
        {create<ast::StageDecoration>(ast::PipelineStage::kFragment)});
 
   ASSERT_TRUE(r()->Resolve()) << r()->error();
diff --git a/src/resolver/struct_storage_class_use_test.cc b/src/resolver/struct_storage_class_use_test.cc
index 8213758100..ac1b8f5927 100644
--- a/src/resolver/struct_storage_class_use_test.cc
+++ b/src/resolver/struct_storage_class_use_test.cc
@@ -39,7 +39,7 @@ TEST_F(ResolverStorageClassUseTest, UnreachableStruct) {
 TEST_F(ResolverStorageClassUseTest, StructReachableFromParameter) {
   auto* s = Structure("S", {Member("a", ty.f32())});
 
-  Func("f", {Var("param", s, ast::StorageClass::kNone)}, ty.void_(), {}, {});
+  Func("f", {Param("param", s)}, ty.void_(), {}, {});
 
   ASSERT_TRUE(r()->Resolve()) << r()->error();
 
diff --git a/src/resolver/type_validation_test.cc b/src/resolver/type_validation_test.cc
index a5dd6bbb1a..ec2113c033 100644
--- a/src/resolver/type_validation_test.cc
+++ b/src/resolver/type_validation_test.cc
@@ -388,8 +388,7 @@ TEST_F(ResolverTypeValidationTest, RuntimeArrayAsParameter_Fail) {
   // fn func(a : array<u32>) {}
   // [[stage(vertex)]] fn main() {}
 
-  auto* param =
-      Var(Source{{12, 34}}, "a", ty.array<i32>(), ast::StorageClass::kNone);
+  auto* param = Param(Source{{12, 34}}, "a", ty.array<i32>());
 
   Func("func", ast::VariableList{param}, ty.void_(),
        ast::StatementList{
diff --git a/src/transform/canonicalize_entry_point_io.cc b/src/transform/canonicalize_entry_point_io.cc
index b263767d09..db1b5a7dfe 100644
--- a/src/transform/canonicalize_entry_point_io.cc
+++ b/src/transform/canonicalize_entry_point_io.cc
@@ -137,8 +137,7 @@ Transform::Output CanonicalizeEntryPointIO::Run(const Program* in,
       ctx.InsertBefore(ctx.src->AST().GlobalDeclarations(), func, in_struct);
 
       // Create a new function parameter using this struct type.
-      auto* struct_param = ctx.dst->Var(new_struct_param_symbol, in_struct,
-                                        ast::StorageClass::kNone);
+      auto* struct_param = ctx.dst->Param(new_struct_param_symbol, in_struct);
       new_parameters.push_back(struct_param);
     }
 
diff --git a/src/transform/spirv.cc b/src/transform/spirv.cc
index bb4f7ae865..6945cbfd19 100644
--- a/src/transform/spirv.cc
+++ b/src/transform/spirv.cc
@@ -159,7 +159,7 @@ void Spirv::HandleEntryPointIOTypes(CloneContext& ctx) const {
 
       // Create a function that writes a return value to all output variables.
       auto* store_value =
-          ctx.dst->Const(store_value_symbol, ctx.Clone(func->return_type()));
+          ctx.dst->Param(store_value_symbol, ctx.Clone(func->return_type()));
       auto return_func_symbol = ctx.dst->Symbols().New();
       auto* return_func = ctx.dst->create<ast::Function>(
           return_func_symbol, ast::VariableList{store_value},
diff --git a/src/writer/hlsl/generator_impl_function_test.cc b/src/writer/hlsl/generator_impl_function_test.cc
index bfd7f8c474..fcf000adf1 100644
--- a/src/writer/hlsl/generator_impl_function_test.cc
+++ b/src/writer/hlsl/generator_impl_function_test.cc
@@ -68,9 +68,7 @@ TEST_F(HlslGeneratorImplTest_Function, Emit_Function_Name_Collision) {
 }
 
 TEST_F(HlslGeneratorImplTest_Function, Emit_Function_WithParams) {
-  Func("my_func",
-       ast::VariableList{Var("a", ty.f32(), ast::StorageClass::kNone),
-                         Var("b", ty.i32(), ast::StorageClass::kNone)},
+  Func("my_func", ast::VariableList{Param("a", ty.f32()), Param("b", ty.i32())},
        ty.void_(),
        ast::StatementList{
            create<ast::ReturnStatement>(),
@@ -114,8 +112,7 @@ TEST_F(HlslGeneratorImplTest_Function,
   // fn frag_main([[location(0)]] foo : f32) -> [[location(1)]] f32 {
   //   return foo;
   // }
-  auto* foo_in =
-      Const("foo", ty.f32(), nullptr, {create<ast::LocationDecoration>(0)});
+  auto* foo_in = Param("foo", ty.f32(), {create<ast::LocationDecoration>(0)});
   Func("frag_main", ast::VariableList{foo_in}, ty.f32(),
        {create<ast::ReturnStatement>(Expr("foo"))},
        {create<ast::StageDecoration>(ast::PipelineStage::kFragment)},
@@ -148,7 +145,7 @@ TEST_F(HlslGeneratorImplTest_Function,
   //   return coord.x;
   // }
   auto* coord_in =
-      Const("coord", ty.vec4<f32>(), nullptr,
+      Param("coord", ty.vec4<f32>(),
             {create<ast::BuiltinDecoration>(ast::Builtin::kFragCoord)});
   Func("frag_main", ast::VariableList{coord_in}, ty.f32(),
        {create<ast::ReturnStatement>(MemberAccessor("coord", "x"))},
@@ -199,7 +196,7 @@ TEST_F(HlslGeneratorImplTest_Function,
            Construct(interface_struct, Expr(0.5f), Expr(0.25f)))},
        {create<ast::StageDecoration>(ast::PipelineStage::kVertex)});
 
-  Func("frag_main", {Const("colors", interface_struct)}, ty.void_(),
+  Func("frag_main", {Param("colors", interface_struct)}, ty.void_(),
        {
            WrapInStatement(
                Const("r", ty.f32(), MemberAccessor(Expr("colors"), "col1"))),
@@ -261,7 +258,7 @@ TEST_F(HlslGeneratorImplTest_Function,
       {Member("pos", ty.vec4<f32>(),
               {create<ast::BuiltinDecoration>(ast::Builtin::kPosition)})});
 
-  Func("foo", {Const("x", ty.f32())}, vertex_output_struct,
+  Func("foo", {Param("x", ty.f32())}, vertex_output_struct,
        {create<ast::ReturnStatement>(Construct(
            vertex_output_struct, Construct(ty.vec4<f32>(), Expr("x"), Expr("x"),
                                            Expr("x"), Expr(1.f))))},
@@ -570,9 +567,7 @@ TEST_F(
              create<ast::LocationDecoration>(0),
          });
 
-  Func("sub_func",
-       ast::VariableList{Var("param", ty.f32(), ast::StorageClass::kNone)},
-       ty.f32(),
+  Func("sub_func", ast::VariableList{Param("param", ty.f32())}, ty.f32(),
        ast::StatementList{
            create<ast::AssignmentStatement>(Expr("bar"), Expr("foo")),
            create<ast::AssignmentStatement>(Expr("val"), Expr("param")),
@@ -626,9 +621,7 @@ TEST_F(HlslGeneratorImplTest_Function,
              create<ast::BuiltinDecoration>(ast::Builtin::kFragDepth),
          });
 
-  Func("sub_func",
-       ast::VariableList{Var("param", ty.f32(), ast::StorageClass::kFunction)},
-       ty.f32(),
+  Func("sub_func", ast::VariableList{Param("param", ty.f32())}, ty.f32(),
        ast::StatementList{
            create<ast::ReturnStatement>(Expr("param")),
        },
@@ -680,9 +673,7 @@ TEST_F(
              create<ast::BuiltinDecoration>(ast::Builtin::kFragDepth),
          });
 
-  Func("sub_func",
-       ast::VariableList{Var("param", ty.f32(), ast::StorageClass::kNone)},
-       ty.f32(),
+  Func("sub_func", ast::VariableList{Param("param", ty.f32())}, ty.f32(),
        ast::StatementList{
            create<ast::AssignmentStatement>(Expr("depth"),
                                             MemberAccessor("coord", "x")),
@@ -735,9 +726,7 @@ TEST_F(HlslGeneratorImplTest_Function,
              create<ast::GroupDecoration>(1),
          });
 
-  Func("sub_func",
-       ast::VariableList{Var("param", ty.f32(), ast::StorageClass::kFunction)},
-       ty.f32(),
+  Func("sub_func", ast::VariableList{Param("param", ty.f32())}, ty.f32(),
        ast::StatementList{
            create<ast::ReturnStatement>(MemberAccessor("coord", "x")),
        },
@@ -785,9 +774,7 @@ TEST_F(HlslGeneratorImplTest_Function,
              create<ast::GroupDecoration>(1),
          });
 
-  Func("sub_func",
-       ast::VariableList{Var("param", ty.f32(), ast::StorageClass::kFunction)},
-       ty.f32(),
+  Func("sub_func", ast::VariableList{Param("param", ty.f32())}, ty.f32(),
        ast::StatementList{
            create<ast::ReturnStatement>(MemberAccessor("coord", "x")),
        },
@@ -932,13 +919,10 @@ void main() {
 }
 
 TEST_F(HlslGeneratorImplTest_Function, Emit_Function_WithArrayParams) {
-  Func(
-      "my_func",
-      ast::VariableList{Var("a", ty.array<f32, 5>(), ast::StorageClass::kNone)},
-      ty.void_(),
-      ast::StatementList{
-          create<ast::ReturnStatement>(),
-      });
+  Func("my_func", ast::VariableList{Param("a", ty.array<f32, 5>())}, ty.void_(),
+       ast::StatementList{
+           create<ast::ReturnStatement>(),
+       });
 
   GeneratorImpl& gen = Build();
 
diff --git a/src/writer/msl/generator_impl_function_test.cc b/src/writer/msl/generator_impl_function_test.cc
index c29db72745..a7660616fa 100644
--- a/src/writer/msl/generator_impl_function_test.cc
+++ b/src/writer/msl/generator_impl_function_test.cc
@@ -49,8 +49,8 @@ using namespace metal;
 
 TEST_F(MslGeneratorImplTest, Emit_Function_WithParams) {
   ast::VariableList params;
-  params.push_back(Var("a", ty.f32(), ast::StorageClass::kNone));
-  params.push_back(Var("b", ty.i32(), ast::StorageClass::kNone));
+  params.push_back(Param("a", ty.f32()));
+  params.push_back(Param("b", ty.i32()));
 
   Func("my_func", params, ty.void_(),
        ast::StatementList{
@@ -96,8 +96,7 @@ TEST_F(MslGeneratorImplTest, Emit_Decoration_EntryPoint_WithInOutVars) {
   // fn frag_main([[location(0)]] foo : f32) -> [[location(1)]] f32 {
   //   return foo;
   // }
-  auto* foo_in =
-      Const("foo", ty.f32(), nullptr, {create<ast::LocationDecoration>(0)});
+  auto* foo_in = Param("foo", ty.f32(), {create<ast::LocationDecoration>(0)});
   Func("frag_main", ast::VariableList{foo_in}, ty.f32(),
        {create<ast::ReturnStatement>(Expr("foo"))},
        {create<ast::StageDecoration>(ast::PipelineStage::kFragment)},
@@ -129,7 +128,7 @@ TEST_F(MslGeneratorImplTest, Emit_Decoration_EntryPoint_WithInOut_Builtins) {
   //   return coord.x;
   // }
   auto* coord_in =
-      Const("coord", ty.vec4<f32>(), nullptr,
+      Param("coord", ty.vec4<f32>(),
             {create<ast::BuiltinDecoration>(ast::Builtin::kFragCoord)});
   Func("frag_main", ast::VariableList{coord_in}, ty.f32(),
        {create<ast::ReturnStatement>(MemberAccessor("coord", "x"))},
@@ -180,7 +179,7 @@ TEST_F(MslGeneratorImplTest,
            Construct(interface_struct, Expr(0.5f), Expr(0.25f)))},
        {create<ast::StageDecoration>(ast::PipelineStage::kVertex)});
 
-  Func("frag_main", {Const("colors", interface_struct)}, ty.void_(),
+  Func("frag_main", {Param("colors", interface_struct)}, ty.void_(),
        {
            WrapInStatement(
                Const("r", ty.f32(), MemberAccessor(Expr("colors"), "col1"))),
@@ -242,7 +241,7 @@ TEST_F(MslGeneratorImplTest,
       {Member("pos", ty.vec4<f32>(),
               {create<ast::BuiltinDecoration>(ast::Builtin::kPosition)})});
 
-  Func("foo", {Const("x", ty.f32())}, vertex_output_struct,
+  Func("foo", {Param("x", ty.f32())}, vertex_output_struct,
        {create<ast::ReturnStatement>(Construct(
            vertex_output_struct, Construct(ty.vec4<f32>(), Expr("x"), Expr("x"),
                                            Expr("x"), Expr(1.f))))},
@@ -393,7 +392,7 @@ TEST_F(
          ast::DecorationList{create<ast::LocationDecoration>(0)});
 
   ast::VariableList params;
-  params.push_back(Var("param", ty.f32(), ast::StorageClass::kNone));
+  params.push_back(Param("param", ty.f32()));
 
   auto body = ast::StatementList{
       create<ast::AssignmentStatement>(Expr("bar"), Expr("foo")),
@@ -450,7 +449,7 @@ TEST_F(MslGeneratorImplTest,
              create<ast::BuiltinDecoration>(ast::Builtin::kFragDepth)});
 
   ast::VariableList params;
-  params.push_back(Var("param", ty.f32(), ast::StorageClass::kFunction));
+  params.push_back(Param("param", ty.f32()));
 
   Func("sub_func", params, ty.f32(),
        ast::StatementList{
@@ -504,7 +503,7 @@ TEST_F(
              create<ast::BuiltinDecoration>(ast::Builtin::kFragDepth)});
 
   ast::VariableList params;
-  params.push_back(Var("param", ty.f32(), ast::StorageClass::kNone));
+  params.push_back(Param("param", ty.f32()));
 
   auto body = ast::StatementList{
       create<ast::AssignmentStatement>(Expr("depth"),
@@ -555,7 +554,7 @@ TEST_F(MslGeneratorImplTest,
                              create<ast::GroupDecoration>(1)});
 
   ast::VariableList params;
-  params.push_back(Var("param", ty.f32(), ast::StorageClass::kFunction));
+  params.push_back(Param("param", ty.f32()));
 
   auto body = ast::StatementList{
       create<ast::ReturnStatement>(MemberAccessor("coord", "x")),
@@ -610,7 +609,7 @@ TEST_F(MslGeneratorImplTest,
                              create<ast::GroupDecoration>(1)});
 
   ast::VariableList params;
-  params.push_back(Var("param", ty.f32(), ast::StorageClass::kFunction));
+  params.push_back(Param("param", ty.f32()));
 
   auto body = ast::StatementList{
       create<ast::ReturnStatement>(MemberAccessor("coord", "b"))};
@@ -666,7 +665,7 @@ TEST_F(MslGeneratorImplTest,
                              create<ast::GroupDecoration>(1)});
 
   ast::VariableList params;
-  params.push_back(Var("param", ty.f32(), ast::StorageClass::kFunction));
+  params.push_back(Param("param", ty.f32()));
 
   auto body = ast::StatementList{
       create<ast::ReturnStatement>(MemberAccessor("coord", "b"))};
@@ -758,7 +757,7 @@ fragment ep_1_out ep_1() {
 
 TEST_F(MslGeneratorImplTest, Emit_Function_WithArrayParams) {
   ast::VariableList params;
-  params.push_back(Var("a", ty.array<f32, 5>(), ast::StorageClass::kNone));
+  params.push_back(Param("a", ty.array<f32, 5>()));
 
   Func("my_func", params, ty.void_(),
        ast::StatementList{
diff --git a/src/writer/spirv/builder_call_test.cc b/src/writer/spirv/builder_call_test.cc
index 3f5311003e..253eef90e4 100644
--- a/src/writer/spirv/builder_call_test.cc
+++ b/src/writer/spirv/builder_call_test.cc
@@ -26,8 +26,8 @@ using BuilderTest = TestHelper;
 
 TEST_F(BuilderTest, Expression_Call) {
   ast::VariableList func_params;
-  func_params.push_back(Var("a", ty.f32(), ast::StorageClass::kFunction));
-  func_params.push_back(Var("b", ty.f32(), ast::StorageClass::kFunction));
+  func_params.push_back(Param("a", ty.f32()));
+  func_params.push_back(Param("b", ty.f32()));
 
   auto* a_func =
       Func("a_func", func_params, ty.f32(),
@@ -46,28 +46,26 @@ TEST_F(BuilderTest, Expression_Call) {
   ASSERT_TRUE(b.GenerateFunction(a_func)) << b.error();
   ASSERT_TRUE(b.GenerateFunction(func)) << b.error();
 
-  EXPECT_EQ(b.GenerateCallExpression(expr), 14u) << b.error();
+  EXPECT_EQ(b.GenerateCallExpression(expr), 12u) << b.error();
   EXPECT_EQ(DumpBuilder(b), R"(OpName %3 "a_func"
 OpName %4 "a"
 OpName %5 "b"
-OpName %12 "main"
+OpName %10 "main"
 %2 = OpTypeFloat 32
 %1 = OpTypeFunction %2 %2 %2
-%11 = OpTypeVoid
-%10 = OpTypeFunction %11
-%15 = OpConstant %2 1
+%9 = OpTypeVoid
+%8 = OpTypeFunction %9
+%13 = OpConstant %2 1
 %3 = OpFunction %2 None %1
 %4 = OpFunctionParameter %2
 %5 = OpFunctionParameter %2
 %6 = OpLabel
-%7 = OpLoad %2 %4
-%8 = OpLoad %2 %5
-%9 = OpFAdd %2 %7 %8
-OpReturnValue %9
+%7 = OpFAdd %2 %4 %5
+OpReturnValue %7
 OpFunctionEnd
-%12 = OpFunction %11 None %10
-%13 = OpLabel
-%14 = OpFunctionCall %2 %3 %15 %15
+%10 = OpFunction %9 None %8
+%11 = OpLabel
+%12 = OpFunctionCall %2 %3 %13 %13
 OpReturn
 OpFunctionEnd
 )");
@@ -75,8 +73,8 @@ OpFunctionEnd
 
 TEST_F(BuilderTest, Statement_Call) {
   ast::VariableList func_params;
-  func_params.push_back(Var("a", ty.f32(), ast::StorageClass::kFunction));
-  func_params.push_back(Var("b", ty.f32(), ast::StorageClass::kFunction));
+  func_params.push_back(Param("a", ty.f32()));
+  func_params.push_back(Param("b", ty.f32()));
 
   auto* a_func =
       Func("a_func", func_params, ty.f32(),
@@ -99,24 +97,22 @@ TEST_F(BuilderTest, Statement_Call) {
   EXPECT_EQ(DumpBuilder(b), R"(OpName %3 "a_func"
 OpName %4 "a"
 OpName %5 "b"
-OpName %12 "main"
+OpName %10 "main"
 %2 = OpTypeFloat 32
 %1 = OpTypeFunction %2 %2 %2
-%11 = OpTypeVoid
-%10 = OpTypeFunction %11
-%15 = OpConstant %2 1
+%9 = OpTypeVoid
+%8 = OpTypeFunction %9
+%13 = OpConstant %2 1
 %3 = OpFunction %2 None %1
 %4 = OpFunctionParameter %2
 %5 = OpFunctionParameter %2
 %6 = OpLabel
-%7 = OpLoad %2 %4
-%8 = OpLoad %2 %5
-%9 = OpFAdd %2 %7 %8
-OpReturnValue %9
+%7 = OpFAdd %2 %4 %5
+OpReturnValue %7
 OpFunctionEnd
-%12 = OpFunction %11 None %10
-%13 = OpLabel
-%14 = OpFunctionCall %2 %3 %15 %15
+%10 = OpFunction %9 None %8
+%11 = OpLabel
+%12 = OpFunctionCall %2 %3 %13 %13
 OpReturn
 OpFunctionEnd
 )");
diff --git a/src/writer/spirv/builder_entry_point_test.cc b/src/writer/spirv/builder_entry_point_test.cc
index a4792e7b68..ea7bad6f4b 100644
--- a/src/writer/spirv/builder_entry_point_test.cc
+++ b/src/writer/spirv/builder_entry_point_test.cc
@@ -44,10 +44,10 @@ TEST_F(BuilderTest, EntryPoint_Parameters) {
   // }
   auto* f32 = ty.f32();
   auto* vec4 = ty.vec4<float>();
-  auto* coord = Var("coord", vec4, ast::StorageClass::kInput, nullptr,
-                    {create<ast::BuiltinDecoration>(ast::Builtin::kFragCoord)});
-  auto* loc1 = Var("loc1", f32, ast::StorageClass::kInput, nullptr,
-                   {create<ast::LocationDecoration>(1u)});
+  auto* coord =
+      Param("coord", vec4,
+            {create<ast::BuiltinDecoration>(ast::Builtin::kFragCoord)});
+  auto* loc1 = Param("loc1", f32, {create<ast::LocationDecoration>(1u)});
   auto* mul = Mul(Expr(MemberAccessor("coord", "x")), Expr("loc1"));
   auto* col = Var("col", f32, ast::StorageClass::kFunction, mul, {});
   Func("frag_main", ast::VariableList{coord, loc1}, ty.void_(),
@@ -109,8 +109,7 @@ TEST_F(BuilderTest, EntryPoint_ReturnValue) {
   // }
   auto* f32 = ty.f32();
   auto* u32 = ty.u32();
-  auto* loc_in = Var("loc_in", u32, ast::StorageClass::kFunction, nullptr,
-                     {create<ast::LocationDecoration>(0)});
+  auto* loc_in = Param("loc_in", u32, {create<ast::LocationDecoration>(0)});
   auto* cond = create<ast::BinaryExpression>(ast::BinaryOp::kGreaterThan,
                                              Expr("loc_in"), Expr(10u));
   Func("frag_main", ast::VariableList{loc_in}, f32,
@@ -203,8 +202,7 @@ TEST_F(BuilderTest, EntryPoint_SharedStruct) {
        {create<ast::ReturnStatement>(vert_retval)},
        {create<ast::StageDecoration>(ast::PipelineStage::kVertex)});
 
-  auto* frag_inputs =
-      Var("inputs", interface, ast::StorageClass::kFunction, nullptr);
+  auto* frag_inputs = Param("inputs", interface);
   Func("frag_main", ast::VariableList{frag_inputs}, ty.f32(),
        {create<ast::ReturnStatement>(MemberAccessor(Expr("inputs"), "value"))},
        {create<ast::StageDecoration>(ast::PipelineStage::kFragment)},
diff --git a/src/writer/spirv/builder_function_test.cc b/src/writer/spirv/builder_function_test.cc
index 66d93dcd8b..be78a581e6 100644
--- a/src/writer/spirv/builder_function_test.cc
+++ b/src/writer/spirv/builder_function_test.cc
@@ -113,8 +113,7 @@ OpFunctionEnd
 }
 
 TEST_F(BuilderTest, Function_WithParams) {
-  ast::VariableList params = {Var("a", ty.f32(), ast::StorageClass::kFunction),
-                              Var("b", ty.i32(), ast::StorageClass::kFunction)};
+  ast::VariableList params = {Param("a", ty.f32()), Param("b", ty.i32())};
 
   Func("a_func", params, ty.f32(),
        ast::StatementList{create<ast::ReturnStatement>(Expr("a"))},
@@ -134,8 +133,7 @@ OpName %6 "b"
 %5 = OpFunctionParameter %2
 %6 = OpFunctionParameter %3
 %7 = OpLabel
-%8 = OpLoad %2 %5
-OpReturnValue %8
+OpReturnValue %5
 OpFunctionEnd
 )") << DumpBuilder(b);
 }
diff --git a/src/writer/wgsl/generator_impl_function_test.cc b/src/writer/wgsl/generator_impl_function_test.cc
index f7f6d6a790..98f3a8da21 100644
--- a/src/writer/wgsl/generator_impl_function_test.cc
+++ b/src/writer/wgsl/generator_impl_function_test.cc
@@ -47,16 +47,14 @@ TEST_F(WgslGeneratorImplTest, Emit_Function) {
 }
 
 TEST_F(WgslGeneratorImplTest, Emit_Function_WithParams) {
-  auto* func =
-      Func("my_func",
-           ast::VariableList{Var("a", ty.f32(), ast::StorageClass::kNone),
-                             Var("b", ty.i32(), ast::StorageClass::kNone)},
-           ty.void_(),
-           ast::StatementList{
-               create<ast::DiscardStatement>(),
-               create<ast::ReturnStatement>(),
-           },
-           ast::DecorationList{});
+  auto* func = Func(
+      "my_func", ast::VariableList{Param("a", ty.f32()), Param("b", ty.i32())},
+      ty.void_(),
+      ast::StatementList{
+          create<ast::DiscardStatement>(),
+          create<ast::ReturnStatement>(),
+      },
+      ast::DecorationList{});
 
   GeneratorImpl& gen = Build();
 
@@ -145,10 +143,10 @@ TEST_F(WgslGeneratorImplTest, Emit_Function_WithDecoration_Multiple) {
 
 TEST_F(WgslGeneratorImplTest, Emit_Function_EntryPoint_Parameters) {
   auto* vec4 = ty.vec4<f32>();
-  auto* coord = Var("coord", vec4, ast::StorageClass::kInput, nullptr,
-                    {create<ast::BuiltinDecoration>(ast::Builtin::kFragCoord)});
-  auto* loc1 = Var("loc1", ty.f32(), ast::StorageClass::kInput, nullptr,
-                   {create<ast::LocationDecoration>(1u)});
+  auto* coord =
+      Param("coord", vec4,
+            {create<ast::BuiltinDecoration>(ast::Builtin::kFragCoord)});
+  auto* loc1 = Param("loc1", ty.f32(), {create<ast::LocationDecoration>(1u)});
   auto* func =
       Func("frag_main", ast::VariableList{coord, loc1}, ty.void_(),
            ast::StatementList{},