spirv-reader: treat function parameters as const declarations

Change-Id: I5e5f35be15737c6dc46bb2e9dc1319f7c403eab8
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/30921
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Commit-Queue: David Neto <dneto@google.com>

src/reader/spirv/function.cc

@@ -614,8 +614,11 @@ bool FunctionEmitter::EmitFunctionDeclaration() {
       [this, &ast_params](const spvtools::opt::Instruction* param) {
         auto* ast_type = parser_impl_.ConvertType(param->type_id());
         if (ast_type != nullptr) {
-          ast_params.emplace_back(parser_impl_.MakeVariable(
-              param->result_id(), ast::StorageClass::kNone, ast_type));
+          auto ast_param = parser_impl_.MakeVariable(
+              param->result_id(), ast::StorageClass::kNone, ast_type);
+          // Parameters are treated as const declarations.
+          ast_param->set_is_const(true);
+          ast_params.emplace_back(std::move(ast_param));
           // The value is accessible by name.
           identifier_values_.insert(param->result_id());
         } else {

src/reader/spirv/function_call_test.cc

@@ -219,12 +219,12 @@ TEST_F(SpvParserTest, EmitStatement_CallWithParams) {
   EXPECT_THAT(module_ast_str, HasSubstr(R"(Module{
   Function x_50 -> __u32
   (
-    Variable{
+    VariableConst{
       x_51
       none
       __u32
     }
-    Variable{
+    VariableConst{
       x_52
       none
       __u32

src/reader/spirv/function_decl_test.cc

@@ -104,17 +104,17 @@ TEST_F(SpvParserTest, EmitFunctionDeclaration_MixedParamTypes) {
   EXPECT_THAT(p->module().to_str(), HasSubstr(R"(
   Function x_100 -> __void
   (
-    Variable{
+    VariableConst{
       a
       none
       __u32
     }
-    Variable{
+    VariableConst{
       b
       none
       __f32
     }
-    Variable{
+    VariableConst{
       c
       none
       __i32
@@ -143,17 +143,17 @@ TEST_F(SpvParserTest, EmitFunctionDeclaration_GenerateParamNames) {
   EXPECT_THAT(p->module().to_str(), HasSubstr(R"(
   Function x_100 -> __void
   (
-    Variable{
+    VariableConst{
       x_14
       none
       __u32
     }
-    Variable{
+    VariableConst{
       x_15
       none
       __f32
     }
-    Variable{
+    VariableConst{
       x_16
       none
       __i32

src/reader/spirv/parser_impl_function_decl_test.cc

@@ -293,17 +293,17 @@ TEST_F(SpvParserTest, EmitFunctions_MixedParamTypes) {
   EXPECT_THAT(module_ast, HasSubstr(R"(
   Function mixed_params -> __void
   (
-    Variable{
+    VariableConst{
       a
       none
       __u32
     }
-    Variable{
+    VariableConst{
       b
       none
       __f32
     }
-    Variable{
+    VariableConst{
       c
       none
       __i32
@@ -332,17 +332,17 @@ TEST_F(SpvParserTest, EmitFunctions_GenerateParamNames) {
   EXPECT_THAT(module_ast, HasSubstr(R"(
   Function mixed_params -> __void
   (
-    Variable{
+    VariableConst{
       x_14
       none
       __u32
     }
-    Variable{
+    VariableConst{
       x_15
       none
       __f32
     }
-    Variable{
+    VariableConst{
       x_16
       none
       __i32