Fix validation of typed select with empty result types (#2708)

include/wabt/ir.h

@@ -701,7 +701,13 @@ class SelectExpr : public ExprMixin<ExprType::Select> {
  public:
   SelectExpr(const Location& loc = Location())
       : ExprMixin<ExprType::Select>(loc) {}
-  TypeVector result_type;
+  // Untyped select is represented by {Type::Void}. An empty result_type
+  // represents an explicit typed select with zero result types and is invalid.
+  TypeVector result_type{Type::Void};
+
+  bool IsUntyped() const {
+    return result_type.size() == 1 && result_type[0] == Type::Void;
+  }
 };
 
 class TableInitExpr : public ExprMixin<ExprType::TableInit> {

src/binary-reader-ir.cc

@@ -1212,7 +1212,11 @@ Result BinaryReaderIR::OnReturnExpr() {
 
 Result BinaryReaderIR::OnSelectExpr(Index result_count, Type* result_types) {
   auto expr_ptr = std::make_unique<SelectExpr>();
-  expr_ptr->result_type.assign(result_types, result_types + result_count);
+  if (result_count == 0) {
+    expr_ptr->result_type = {Type::Void};
+  } else {
+    expr_ptr->result_type.assign(result_types, result_types + result_count);
+  }
   return AppendExpr(std::move(expr_ptr));
 }
 

src/binary-reader.cc

@@ -813,6 +813,7 @@ Result BinaryReader::ReadInstructions(Offset end_offset, const char* context) {
       case Opcode::SelectT: {
         Index num_results;
         CHECK_RESULT(ReadCount(&num_results, "num result types"));
+        ERROR_IF(num_results == 0, "invalid arity in select instruction: 0.");
 
         result_types_.resize(num_results);
         for (Index i = 0; i < num_results; ++i) {
@@ -825,13 +826,8 @@ Result BinaryReader::ReadInstructions(Offset end_offset, const char* context) {
           result_types_[i] = result_type;
         }
 
-        if (num_results) {
-          CALLBACK(OnSelectExpr, num_results, result_types_.data());
-          CALLBACK(OnOpcodeType, result_types_[0]);
-        } else {
-          CALLBACK(OnSelectExpr, 0, NULL);
-          CALLBACK0(OnOpcodeBare);
-        }
+        CALLBACK(OnSelectExpr, num_results, result_types_.data());
+        CALLBACK(OnOpcodeType, result_types_[0]);
         break;
       }
 

src/binary-writer.cc

@@ -1081,7 +1081,7 @@ void BinaryWriter::WriteExpr(const Func* func, const Expr* expr) {
       break;
     case ExprType::Select: {
       auto* select_expr = cast<SelectExpr>(expr);
-      if (select_expr->result_type.empty()) {
+      if (select_expr->IsUntyped()) {
         WriteOpcode(stream_, Opcode::Select);
       } else {
         WriteOpcode(stream_, Opcode::SelectT);

src/validator.cc

@@ -589,8 +589,21 @@ Result Validator::OnReturnCallRefExpr(ReturnCallRefExpr* expr) {
 }
 
 Result Validator::OnSelectExpr(SelectExpr* expr) {
-  result_ |= validator_.OnSelect(expr->loc, expr->result_type.size(),
-                                 expr->result_type.data());
+  Index result_count;
+  Type* result_types = nullptr;
+
+  if (expr->result_type.empty()) {
+    validator_.PrintError(expr->loc, "invalid arity in select instruction: 0.");
+    result_ |= Result::Error;
+    result_count = 0;
+  } else if (expr->IsUntyped()) {
+    result_count = 0;
+  } else {
+    result_count = expr->result_type.size();
+    result_types = expr->result_type.data();
+  }
+
+  result_ |= validator_.OnSelect(expr->loc, result_count, result_types);
   return Result::Ok;
 }
 

src/wast-parser.cc

@@ -2538,6 +2538,7 @@ Result WastParser::ParsePlainInstr(std::unique_ptr<Expr>* out_expr) {
       ResolveTypeVector result_type(&expr->result_type);
       if (options_->features.reference_types_enabled() &&
           PeekMatchLpar(TokenType::Result)) {
+        expr->result_type.clear();
         CHECK_RESULT(ParseResultList(&expr->result_type, &result_type.vars));
       }
       *out_expr = std::move(expr);

src/wat-writer.cc

@@ -977,7 +977,12 @@ Result WatWriter::ExprVisitorDelegate::OnReturnCallRefExpr(
 
 Result WatWriter::ExprVisitorDelegate::OnSelectExpr(SelectExpr* expr) {
   writer_->WritePutsSpace(Opcode::Select_Opcode.GetName());
-  if (!expr->result_type.empty()) {
+  if (expr->IsUntyped()) {
+    // no result annotation
+  } else if (expr->result_type.empty()) {
+    writer_->WriteOpenSpace("result");
+    writer_->WriteCloseSpace();
+  } else {
     writer_->WriteTypes(expr->result_type, "result");
   }
   writer_->WriteNewline(NO_FORCE_NEWLINE);

test/binary/bad-select-empty-result.txt

@@ -0,0 +1,26 @@
+;;; TOOL: run-gen-wasm-bad
+;;; ERROR: 1
+;;; RUN: %(wasm-interp)s --enable-all %(temp_file)s.wasm --run-export=run
+;;; ERROR3: 1
+magic
+version
+section(TYPE) { count[1] function params[0] results[1] i32 }
+section(FUNCTION) { count[1] type[0] }
+section(EXPORT) { count[1] str("run") func_kind 0 }
+section(CODE) {
+  count[1]
+  func {
+    locals[0]
+    i32.const 42
+    i32.const 100
+    i32.const 1
+    select_t[0x1c]
+    result_count[0x00]
+    end
+  }
+}
+(;; STDERR ;;;
+0000029: error: invalid arity in select instruction: 0.
+0000029: error: invalid arity in select instruction: 0.
+0000029: error: invalid arity in select instruction: 0.
+;;; STDERR ;;)

test/parse/expr/bad-select-empty-result.txt

@@ -0,0 +1,14 @@
+;;; TOOL: wat2wasm
+;;; ERROR: 1
+(module
+  (func
+    i32.const 42
+    i32.const 100
+    i32.const 1
+    select (result)
+    drop))
+(;; STDERR ;;;
+out/test/parse/expr/bad-select-empty-result.txt:8:5: error: invalid arity in select instruction: 0.
+    select (result)
+    ^^^^^^
+;;; STDERR ;;)

test/spec/function-references/select.txt

@@ -12,8 +12,7 @@ out/test/spec/function-references/select.wast:364: assert_invalid passed:
   out/test/spec/function-references/select/select.1.wasm:000001c: error: type mismatch in select, expected [any, any, i32] but got [i32]
   000001c: error: OnSelectExpr callback failed
 out/test/spec/function-references/select.wast:368: assert_invalid passed:
-  out/test/spec/function-references/select/select.2.wasm:000001c: error: type mismatch in select, expected [any, any, i32] but got [i32]
-  000001c: error: OnSelectExpr callback failed
+  000001d: error: invalid arity in select instruction: 0.
 out/test/spec/function-references/select.wast:372: assert_invalid passed:
   out/test/spec/function-references/select/select.3.wasm:0000027: error: invalid arity in select instruction: 2.
   0000027: error: OnSelectExpr callback failed

test/spec/select.txt

@@ -7,8 +7,7 @@ out/test/spec/select.wast:320: assert_invalid passed:
   out/test/spec/select/select.1.wasm:000001c: error: type mismatch in select, expected [any, any, i32] but got [i32]
   000001c: error: OnSelectExpr callback failed
 out/test/spec/select.wast:324: assert_invalid passed:
-  out/test/spec/select/select.2.wasm:000001c: error: type mismatch in select, expected [any, any, i32] but got [i32]
-  000001c: error: OnSelectExpr callback failed
+  000001d: error: invalid arity in select instruction: 0.
 out/test/spec/select.wast:328: assert_invalid passed:
   out/test/spec/select/select.3.wasm:0000027: error: invalid arity in select instruction: 2.
   0000027: error: OnSelectExpr callback failed