ps6: task 1

ps6/src/emit.h

@@ -65,6 +65,7 @@
   EMIT("movzbq %s, %s", (byte_reg), (full_reg)) // full_reg <- byte_reg
 
 #define JNE(label) EMIT("jne %s", (label)) // Conditional jump (not equal)
+#define JE(label) EMIT("je %s", (label)) // Conditional jump (equal)
 #define JMP(label) EMIT("jmp %s", (label)) // Unconditional jump
 
 // Bitwise and

ps6/src/generator.c

@@ -445,6 +445,8 @@ static void generate_return_statement(node_t* statement)
   EMIT("jmp .%s.epilogue", current_function->name);
 }
 
+int if_counter = 0;
+
 static void generate_if_statement(node_t* statement)
 {
   // TODO (Task 1):
@@ -453,6 +455,32 @@ static void generate_if_statement(node_t* statement)
 
   // You will need to define your own unique labels for this if statement,
   // so consider using a global variable as a counter to give each label a suffix unique to this if.
+  int arity = statement->n_children;
+  assert(arity == 2 || arity == 3);
+  bool do_else = arity == 3;
+
+  node_t *condition = statement->children[0];
+  node_t *then_body = statement->children[1];
+
+  char endif_label[8];
+  snprintf(endif_label, 8, "ENDIF%d", if_counter);
+  char else_label[8];
+  snprintf(else_label, 8, "ELSE%d", if_counter);
+
+  if_counter++;
+
+  generate_expression(condition);
+  CMPQ("$0", RAX);
+  JE(else_label);
+  generate_statement(then_body);
+  JMP(endif_label);
+  
+  LABEL("%s", else_label);
+  if (do_else) {
+    node_t *else_body = statement->children[2];
+    generate_statement(else_body);
+  }
+  LABEL("%s", endif_label);
 }
 
 static void generate_while_statement(node_t* statement)