fixes

examples/issue-0013.sx

@@ -0,0 +1,36 @@
+// issue-0013: += on global variables reads initial value instead of current value
+//
+// `g_counter += 1` compiles as `store(initial_value + 1)` instead of
+// `store(load(g_counter) + 1)`. So it always produces the same result.
+//
+// Workaround: use `g_counter = g_counter + 1` instead of `g_counter += 1`
+
+#import "modules/std.sx";
+
+g_counter : s64 = 0;
+
+tick :: () {
+    g_counter += 1;
+    print("counter={}\n", g_counter);
+}
+
+main :: () -> void {
+    // Test 1: += always produces 1 (BUG)
+    out("--- Test 1: += (broken) ---\n");
+    out("Expected: 1, 2, 3\n");
+    i : s64 = 0;
+    while i < 3 {
+        tick();
+        i += 1;
+    }
+
+    // Test 2: manual read-modify-write works correctly
+    out("--- Test 2: = x + 1 (works) ---\n");
+    out("Expected: 2, 3, 4\n");
+    g_counter = g_counter + 1;
+    print("counter={}\n", g_counter);
+    g_counter = g_counter + 1;
+    print("counter={}\n", g_counter);
+    g_counter = g_counter + 1;
+    print("counter={}\n", g_counter);
+}