linker: skip default palette + rendering enable for non-visual ROMs

Add an `__oam_used` marker dropped by IrOp::DrawSprite codegen, and compute a `has_visual_output` flag in the linker from the marker plus the presence of any user palette / sprite / background. When that flag is false — i.e. a purely audio- or compute-only program — the linker skips both the reset-time default palette load and the `gen_enable_rendering` PPU_MASK write. `gen_init` already leaves rendering disabled, so the PPU stays silent and palette RAM stays in its power-on state. ~72 bytes reclaimed for non-visual programs. Caveat: audio-only ROMs now display an undefined backdrop colour instead of the default-palette black. jsnes renders that as a mid-grey; Mesen/real hardware may vary. Programs that want a specific backdrop should declare their own palette. The golden png for `examples/sfx_pitch_envelope` (the one audio-only example in the set) flips from all-black to all-grey to document this. `__oam_used` is also consumed by the next two commits (default smiley CHR gate, OAM DMA gate), so introducing it here keeps the marker table coherent in one place. Emitting it inline in the DrawSprite codegen path does shift a handful of peephole-block boundaries for programs that draw — pixel goldens flip for `examples/comparisons` by 56 out of 61440 pixels (a one-pixel sprite-position drift caused by accumulated branch-page-crossing cycle drift), a cousin of the audio-hash drift already documented in the prior two commits. https://claude.ai/code/session_016kM6P7PukktBDqTZexrrAN
2026-07-08 08:55:38 +00:00 · 2026-04-16 13:21:56 +00:00 · 2026-04-16 13:21:56 +00:00 · 7533ac281e
commit 7533ac281e
parent 37974611ae
42 changed files with 111 additions and 34 deletions
--- a/examples/audio_demo.nes
+++ b/examples/audio_demo.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/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/pong.nes
+++ b/examples/pong.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/two_player.nes
+++ b/examples/two_player.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