Update comments and small fixes

src/llvm_ir_generator.cpp

@@ -199,7 +199,7 @@ void LLVMIRGenerator::Visit(const ArrDeclNode& arr_decl) {
   }
 
   auto arr_decl_type = dynamic_cast<ArrType*>(arr_decl.type.get());
-  // This vector stores the initialize values for an array.
+  // This vector stores the initialize values for a global array.
   std::vector<llvm::Constant*> arr_elems{};
   for (auto i = std::size_t{0}, e = arr_decl_type->len(),
             init_len = arr_decl.init_list.size();
@@ -220,13 +220,12 @@ void LLVMIRGenerator::Visit(const ArrDeclNode& arr_decl) {
         builder_.CreateStore(init_val, res_addr);
       }
     } else {
-      // set remaining elements as 0
       auto zero = llvm::ConstantInt::get(builder_.getInt32Ty(), 0, true);
+      // A global array is always initialized to 0,
+      // but a local array remains uninitialized if no values are provided.
       if (arr_decl.is_global) {
         arr_elems.push_back(zero);
-      } else if (!arr_decl.is_global && 0 < init_len) {
-        // If array is in local scope and its initialized values is not
-        // declared, then compiler will not set element values to 0.
+      } else if (!arr_decl.is_global && init_len != 0) {
         auto res_addr = builder_.CreateConstInBoundsGEP2_32(
             type, id_to_val.at(arr_decl.id), 0, i);
         builder_.CreateStore(zero, res_addr);

src/qbe_ir_generator.cpp

@@ -231,10 +231,8 @@ void QbeIrGenerator::Visit(const ArrDeclNode& arr_decl) {
     global_var_init_vals.clear();
     auto arr_size = arr_type->len();
     auto init_len = arr_decl.init_list.size();
-    // The predicate of this loop guarantees that it doesn't go out of bound if
-    // the number of initialized elements is less than the array declaration
-    // size.
-    for (auto i = std::size_t{0}; i < arr_size && i < init_len; ++i) {
+    assert(init_len <= arr_size);
+    for (auto i = std::size_t{0}; i < init_len; ++i) {
       auto& arr_init = arr_decl.init_list.at(i);
       arr_init->Accept(*this);
       Write_("{}", GenerateQBEInit(global_var_init_vals.at(i)));
@@ -263,7 +261,7 @@ void QbeIrGenerator::Visit(const ArrDeclNode& arr_decl) {
     // explicitly, its value is indeterminate.
     for (auto i = std::size_t{0}, e = arr_type->len(),
               init_len = arr_decl.init_list.size();
-         i < e && 0 < init_len; ++i) {
+         i < e && init_len != 0; ++i) {
       if (i < init_len) {
         auto& arr_init = arr_decl.init_list.at(i);
         arr_init->Accept(*this);

test/codegen/array.c

@@ -22,6 +22,7 @@ int main() {
   __builtin_print(e[1]);
   __builtin_print(e[2]);
 
+  // NOTE: Local scope array should not be 0-initialized, and the generated IR has to be checked manually.
   int f[2];
   return 0;
 }