runtime: gate controller-2 reads in NMI on __p2_input_used

Drop the three-instruction JOY2 shift block (`LDA $4017 / LSR A / ROL ZP_INPUT_P2`) from inside the NMI's 8-iteration input loop when user code never reads controller 2. IR codegen emits the `__p2_input_used` marker from `IrOp::ReadInput(_, 1)`; the linker threads the flag through a new `NmiOptions::has_p2_input` bool, and `gen_nmi` writes the shift block only when the flag is set. Savings for single-player programs: - ~6 bytes of NMI code. - ~30 cycles per frame (3 instructions × 8 loop iterations, each 6-8 cycles depending on addressing — LDA abs is 4, LSR A is 2, ROL zp is 5, so ~11 cycles × 8 = ~88 cycles; rounded down for the page-crossing penalty landing differently in the new layout). This commit also fixes the IR codegen to drop the matching `__p1_input_used` marker from `IrOp::ReadInput(_, 0)`, even though the next commit is the one that actually consumes it. Landing the two markers together keeps the IR codegen's per-op bookkeeping coherent. Six audio goldens flip (every program that reads input + plays audio) with the expected NMI-layout-shift cycle drift. https://claude.ai/code/session_016kM6P7PukktBDqTZexrrAN
2026-07-08 08:55:38 +00:00 · 2026-04-16 13:43:33 +00:00 · 2026-04-16 13:43:33 +00:00 · 0de1d60c33
commit 0de1d60c33
parent bd30ac3010
40 changed files with 70 additions and 11 deletions
--- a/examples/arrays_and_functions.nes
+++ b/examples/arrays_and_functions.nes
--- a/examples/audio_demo.nes
+++ b/examples/audio_demo.nes
--- a/examples/auto_chr_background.nes
+++ b/examples/auto_chr_background.nes
--- a/examples/bitwise_ops.nes
+++ b/examples/bitwise_ops.nes
--- a/examples/bouncing_ball.nes
+++ b/examples/bouncing_ball.nes
--- a/examples/coin_cavern.nes
+++ b/examples/coin_cavern.nes
--- a/examples/comparisons.nes
+++ b/examples/comparisons.nes
--- a/examples/friendly_assets.nes
+++ b/examples/friendly_assets.nes
--- a/examples/function_chain.nes
+++ b/examples/function_chain.nes
--- a/examples/hello_sprite.nes
+++ b/examples/hello_sprite.nes
--- a/examples/inline_asm_demo.nes
+++ b/examples/inline_asm_demo.nes
--- a/examples/logic_ops.nes
+++ b/examples/logic_ops.nes
--- a/examples/loop_break_continue.nes
+++ b/examples/loop_break_continue.nes
--- a/examples/match_demo.nes
+++ b/examples/match_demo.nes
--- a/examples/metasprite_demo.nes
+++ b/examples/metasprite_demo.nes
--- a/examples/mmc1_banked.nes
+++ b/examples/mmc1_banked.nes
--- a/examples/mmc3_per_state_split.nes
+++ b/examples/mmc3_per_state_split.nes
--- a/examples/nested_structs.nes
+++ b/examples/nested_structs.nes
--- a/examples/noise_triangle_sfx.nes
+++ b/examples/noise_triangle_sfx.nes
--- a/examples/palette_and_background.nes
+++ b/examples/palette_and_background.nes
--- a/examples/platformer.nes
+++ b/examples/platformer.nes
--- a/examples/scanline_split.nes
+++ b/examples/scanline_split.nes
--- a/examples/sfx_pitch_envelope.nes
+++ b/examples/sfx_pitch_envelope.nes
--- a/examples/sprite_flicker_demo.nes
+++ b/examples/sprite_flicker_demo.nes
--- a/examples/sprites_and_palettes.nes
+++ b/examples/sprites_and_palettes.nes
--- a/examples/state_machine.nes
+++ b/examples/state_machine.nes
--- a/examples/structs_enums_for.nes
+++ b/examples/structs_enums_for.nes
--- a/examples/uxrom_banked.nes
+++ b/examples/uxrom_banked.nes
--- a/examples/uxrom_banked_to_banked.nes
+++ b/examples/uxrom_banked_to_banked.nes
--- a/examples/uxrom_user_banked.nes
+++ b/examples/uxrom_user_banked.nes
--- a/examples/war.nes
+++ b/examples/war.nes