IR codegen: Player 2 controller support

ReadInput now takes an explicit player index (0 = P1, 1 = P2). The IR
lowering for ButtonRead threads the player through, and the IR codegen
selects the correct zero-page input byte ($01 for P1, $08 for P2).

https://claude.ai/code/session_01W6eQFStA66EuMKHUFo2rx3

src/codegen/ir_codegen.rs

@@ -407,8 +407,10 @@ impl<'a> IrCodeGen<'a> {
                 self.load_temp(*x);
                 self.emit(STA, AM::Absolute(base + 3));
             }
-            IrOp::ReadInput(dest) => {
-                self.emit(LDA, AM::ZeroPage(0x01)); // ZP_INPUT_P1
+            IrOp::ReadInput(dest, player) => {
+                // $01 = P1 input byte, $08 = P2 input byte
+                let addr = if *player == 1 { 0x08 } else { 0x01 };
+                self.emit(LDA, AM::ZeroPage(addr));
                 self.store_temp(*dest);
             }
             IrOp::WaitFrame => {

src/ir/lowering.rs

@@ -544,11 +544,15 @@ impl LoweringContext {
                 self.emit(IrOp::Call(Some(t), name.clone(), arg_temps));
                 t
             }
-            Expr::ButtonRead(_, button, _) => {
+            Expr::ButtonRead(player, button, _) => {
                 // Button reads: read the input byte, mask with the button bit.
-                // (Player selection is ignored here; IR codegen handles it.)
+                // Player 1 reads from $01, player 2 reads from $08.
+                let player_index = match player {
+                    Some(Player::P2) => 1u8,
+                    _ => 0u8,
+                };
                 let input = self.fresh_temp();
-                self.emit(IrOp::ReadInput(input));
+                self.emit(IrOp::ReadInput(input, player_index));
                 let mask = button_mask(button);
                 let mask_temp = self.fresh_temp();
                 self.emit(IrOp::LoadImm(mask_temp, mask));

src/ir/mod.rs

@@ -124,8 +124,9 @@ pub enum IrOp {
         y: IrTemp,
         frame: Option<IrTemp>,
     },
-    /// Read the current player 1 input byte into a temp.
-    ReadInput(IrTemp),
+    /// Read a controller input byte into a temp.
+    /// Second arg: 0 for player 1, 1 for player 2.
+    ReadInput(IrTemp, u8),
     WaitFrame,
     Transition(String),
 

src/ir/tests.rs

@@ -152,7 +152,7 @@ fn lower_button_read() {
         .blocks
         .iter()
         .flat_map(|b| &b.ops)
-        .any(|op| matches!(op, IrOp::ReadInput(_)));
+        .any(|op| matches!(op, IrOp::ReadInput(_, _)));
     assert!(has_input, "button read should emit ReadInput op");
 }
 

src/optimizer/mod.rs

@@ -379,7 +379,7 @@ fn collect_source_temps(op: &IrOp, used: &mut HashSet<IrTemp>) {
                 used.insert(*f);
             }
         }
-        IrOp::ReadInput(_) | IrOp::WaitFrame | IrOp::Transition(_) | IrOp::SourceLoc(_) => {}
+        IrOp::ReadInput(_, _) | IrOp::WaitFrame | IrOp::Transition(_) | IrOp::SourceLoc(_) => {}
     }
 }
 
@@ -406,7 +406,7 @@ fn op_dest(op: &IrOp) -> Option<IrTemp> {
         | IrOp::CmpGtEq(d, _, _)
         | IrOp::ArrayLoad(d, _, _) => Some(*d),
         IrOp::Call(dest, _, _) => *dest,
-        IrOp::ReadInput(d) => Some(*d),
+        IrOp::ReadInput(d, _) => Some(*d),
         IrOp::StoreVar(_, _)
         | IrOp::ArrayStore(_, _, _)
         | IrOp::DrawSprite { .. }