parser: Implement variable assignment

This commit introduces variable assignment making it possible to
change a variable value. Example:

  myvar: i32 = 1;
  myvar = 2;

Signed-off-by: Johnny Richard <johnny@johnnyrichard.com>
Co-authored-by: Carlos Maniero <carlos@maniero.me>

1 files changed, 51 insertions, 7 deletions

diff --git a/src/gas_assembly_generator.c b/src/gas_assembly_generator.c
index dd5d240..fca02ed 100644
--- a/src/gas_assembly_generator.c
+++ b/src/gas_assembly_generator.c
@@ -37,6 +37,9 @@ gas_assembly_generator_compile_return_stmt(gas_assembly_generator_t *gen, ast_re
 static void
 gas_assembly_generator_compile_variable_declaration(gas_assembly_generator_t *gen,
                                                     ast_variable_declaration_t *variable_declaration);
+static void
+gas_assembly_generator_compile_variable_assignment(gas_assembly_generator_t *gen,
+                                                   ast_variable_assignment_t *variable_assignment);
 
 static void
 gas_assembly_generator_compile_variable(gas_assembly_generator_t *gen, ast_variable_t *variable);
@@ -81,6 +84,18 @@ ref_entry_new(void)
   return entry;
 }
 
+static ref_entry_t *
+find_ref_entry(vector_t *refs, ast_identifier_t *identifier)
+{
+  for (int i = refs->size - 1; i >= 0; --i) {
+    ref_entry_t *entry = (ref_entry_t *)vector_at(refs, i);
+    if (entry->id == identifier) {
+      return entry;
+    }
+  }
+  return NULL;
+}
+
 void
 gas_assembly_generator_init(gas_assembly_generator_t *gen, FILE *stream)
 {
@@ -114,6 +129,9 @@ gas_assembly_generator_compile(gas_assembly_generator_t *gen, ast_node_t *ast)
     case AST_VARIABLE_DECLARATION:
       gas_assembly_generator_compile_variable_declaration(gen, &ast->data.variable_declaration);
       break;
+    case AST_VARIABLE_ASSIGNMENT:
+      gas_assembly_generator_compile_variable_assignment(gen, &ast->data.variable_assignment);
+      break;
     case AST_VARIABLE:
       gas_assembly_generator_compile_variable(gen, &ast->data.variable);
       break;
@@ -190,16 +208,42 @@ gas_assembly_generator_compile_variable_declaration(gas_assembly_generator_t *ge
 }
 
 static void
-gas_assembly_generator_compile_variable(gas_assembly_generator_t *gen, ast_variable_t *variable)
+gas_assembly_generator_compile_variable_assignment(gas_assembly_generator_t *gen,
+                                                   ast_variable_assignment_t *variable_assignment)
 {
-  ref_entry_t *entry = NULL;
-  for (int i = gen->refs->size - 1; i >= 0; --i) {
-    ref_entry_t *entry_tmp = (ref_entry_t *)vector_at(gen->refs, i);
-    if (entry_tmp->id == variable->identifier) {
-      entry = entry_tmp;
+  ref_entry_t *entry = find_ref_entry(gen->refs, variable_assignment->identifier);
+  assert(entry && "reference not found");
+
+  gas_assembly_generator_compile(gen, variable_assignment->expression);
+
+  switch (gen->latest_evaluation.kind) {
+    case EVALUATION_RESULT_AS_LITERAL_INTEGER:
+      fprintf(gen->stream, "  movq $%ld, %d(%%rbp)\n", gen->latest_evaluation.data.literal_int, entry->stack_offset);
       break;
-    }
+    case EVALUATION_RESULT_ON_RAX:
+      fprintf(gen->stream, "  mov %%rax, %d(%%rbp)\n", entry->stack_offset);
+      break;
+    case EVALUATION_RESULT_ON_STACK:
+      fprintf(gen->stream, "  movq %d(%%rbp), %%rax\n", gen->latest_evaluation.data.stack_offset);
+      fprintf(gen->stream, "  movq %%rax, %d(%%rbp)\n", entry->stack_offset);
+      break;
+    case EVALUATION_RESULT_VOID:
+      assert(false && "Unexpected void result for variable declaration");
+      // FIXME: store the latest node at latest evaluation and print_ast
   }
+  // Today we dont't support chain-assignment like this:
+  //
+  //   a = b = 1;
+  //
+  // If we start supporting it, we need to change the latest evaluation kind to
+  // stack.
+  gen->latest_evaluation.kind = EVALUATION_RESULT_VOID;
+}
+
+static void
+gas_assembly_generator_compile_variable(gas_assembly_generator_t *gen, ast_variable_t *variable)
+{
+  ref_entry_t *entry = find_ref_entry(gen->refs, variable->identifier);
   assert(entry && "reference not found");
   gas_assembly_generator_set_latest_evaluation_on_stack(gen, entry->stack_offset);
 }