compiler working for some mathematical expressions, function calls and

simple conditionals

c_compiler/src/registers.rs

@@ -81,7 +81,17 @@ impl RegisterAllocator {
     }
 
     /// Free a temporary register after use
+    /// NOTE: This will NOT free registers that contain variables!
+    /// Variables persist throughout their scope and must not be freed
     pub fn free_temp(&mut self, reg: &str) {
+        // Check if this register contains a variable
+        if self.register_contents.contains_key(reg) {
+            // This register holds a variable - don't free it!
+            // Variables are only freed when they go out of scope via free_var()
+            return;
+        }
+
+        // This is a true temporary - safe to free
         self.in_use.insert(reg.to_string(), false);
     }
 
@@ -243,6 +253,16 @@ impl RegisterAllocator {
         self.variable_locations.remove(var_name);
     }
 
+    /// Get list of registers that contain variables and are in use
+    /// These need to be saved before function calls
+    pub fn get_caller_saved_registers(&self) -> Vec<String> {
+        self.register_contents
+            .iter()
+            .filter(|(reg, _)| *self.in_use.get(*reg).unwrap_or(&false))
+            .map(|(reg, _)| reg.clone())
+            .collect()
+    }
+
     /// Save caller-saved registers before a function call
     /// Returns assembly code to save them
     pub fn save_caller_saved(&mut self) -> Vec<String> {