[spirv-reader] Support Location on module vars

Bug: tint:3
Change-Id: If7fc85251cbffab477b0b4f86c204de6c6a853f6
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/25103
Reviewed-by: dan sinclair <dsinclair@chromium.org>

src/reader/spirv/parser_impl.cc

@@ -942,6 +942,15 @@ std::unique_ptr<ast::Variable> ParserImpl::MakeVariable(uint32_t id,
       ast_decorations.emplace_back(
           std::make_unique<ast::BuiltinDecoration>(ast_builtin));
     }
+    if (deco[0] == SpvDecorationLocation) {
+      if (deco.size() != 2) {
+        Fail() << "malformed Location decoration on ID " << id
+               << ": requires one literal operand";
+        return nullptr;
+      }
+      ast_decorations.emplace_back(
+          std::make_unique<ast::LocationDecoration>(deco[1]));
+    }
   }
   if (!ast_decorations.empty()) {
     auto decorated_var =

src/reader/spirv/parser_impl_module_var_test.cc

@@ -1117,6 +1117,57 @@ TEST_F(SpvParserTest, ModuleScopeVar_StructUndefInitializer) {
       << module_str;
 }
 
+TEST_F(SpvParserTest, ModuleScopeVar_LocationDecoration_Valid) {
+  auto* p = parser(test::Assemble(R"(
+     OpName %myvar "myvar"
+     OpDecorate %myvar Location 3
+)" + CommonTypes() + R"(
+     %ptr = OpTypePointer Input %uint
+     %myvar = OpVariable %ptr Input
+  )"));
+  ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << p->error();
+  EXPECT_TRUE(p->error().empty());
+  const auto module_str = p->module().to_str();
+  EXPECT_THAT(module_str, HasSubstr(R"(
+  DecoratedVariable{
+    Decorations{
+      LocationDecoration{3}
+    }
+    myvar
+    in
+    __u32
+  })"))
+      << module_str;
+}
+
+TEST_F(SpvParserTest,
+       ModuleScopeVar_LocationDecoration_MissingOperandWontAssemble) {
+  const auto assembly = R"(
+     OpName %myvar "myvar"
+     OpDecorate %myvar Location
+)" + CommonTypes() + R"(
+     %ptr = OpTypePointer Input %uint
+     %myvar = OpVariable %ptr Input
+  )";
+  EXPECT_THAT(test::AssembleFailure(assembly),
+              Eq("4:4: Expected operand, found next instruction instead."));
+}
+
+TEST_F(SpvParserTest,
+       ModuleScopeVar_LocationDecoration_TwoOperandsWontAssemble) {
+  const auto assembly = R"(
+     OpName %myvar "myvar"
+     OpDecorate %myvar Location 3 4
+)" + CommonTypes() + R"(
+     %ptr = OpTypePointer Input %uint
+     %myvar = OpVariable %ptr Input
+  )";
+  EXPECT_THAT(
+      test::AssembleFailure(assembly),
+      Eq("2:34: Expected <opcode> or <result-id> at the beginning of an "
+         "instruction, found '4'."));
+}
+
 }  // namespace
 }  // namespace spirv
 }  // namespace reader