mirror of
https://github.com/imjasonh/nescript
synced 2026-07-08 17:06:04 +00:00
df71c2bf50
The IR codegen lowers `i -= 1` (and friends) into a `LoadImm temp,
1; Sub d, i, temp; StoreVar i, d` triple, and the optimizer
strength-reduces the Sub+StoreVar pair into `DEC i`. The
constant-load-into-A that used to feed the Sub stays around as a
dead `LDA #1`:
LDA #1
DEC ZeroPage(rem)
JMP Label("__ir_blk_while_cond_…")
`remove_dead_loads` was set up to drop exactly this pattern but
gave up at the trailing `JMP` because it couldn't reason about
flow. Extend it to follow one unconditional `JMP <label>` to its
target and resume the dead-store scan from the next instruction.
The first instruction past the loop-condition label is reliably an
`LDA loop_var`, which overwrites A without reading it — so the
`LDA #1` is correctly identified as dead.
Conditional branches still end the scan (their not-taken path is
unconstrained) and only one JMP is followed (to keep the analysis
local). For SHA-256 specifically this drops two `LDA #1`s per
iteration of the rotate/shift bit-loops — about 1K cycles per
block. The same pattern fires across most examples' loop tails.
Verified: cargo test/clippy/fmt clean on rustc 1.95.0; emulator
harness 34/34; reproducibility diff clean; SHA-256 of "NES" still
computes to AE9145DB…4E0D. The cycle drift refreshes the four
audio hashes / golden frames timing-sensitive examples already
tracked.
https://claude.ai/code/session_01FRmSBruVWCufm3LsUVMs8v
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|---|---|---|
| .. | ||
| arrays_and_functions.audio.hash | ||
| arrays_and_functions.png | ||
| audio_demo.audio.hash | ||
| audio_demo.png | ||
| auto_chr_background.audio.hash | ||
| auto_chr_background.png | ||
| bitwise_ops.audio.hash | ||
| bitwise_ops.png | ||
| bouncing_ball.audio.hash | ||
| bouncing_ball.png | ||
| coin_cavern.audio.hash | ||
| coin_cavern.png | ||
| comparisons.audio.hash | ||
| comparisons.png | ||
| friendly_assets.audio.hash | ||
| friendly_assets.png | ||
| function_chain.audio.hash | ||
| function_chain.png | ||
| hello_sprite.audio.hash | ||
| hello_sprite.png | ||
| inline_asm_demo.audio.hash | ||
| inline_asm_demo.png | ||
| logic_ops.audio.hash | ||
| logic_ops.png | ||
| loop_break_continue.audio.hash | ||
| loop_break_continue.png | ||
| match_demo.audio.hash | ||
| match_demo.png | ||
| metasprite_demo.audio.hash | ||
| metasprite_demo.png | ||
| mmc1_banked.audio.hash | ||
| mmc1_banked.png | ||
| mmc3_per_state_split.audio.hash | ||
| mmc3_per_state_split.png | ||
| nested_structs.audio.hash | ||
| nested_structs.png | ||
| noise_triangle_sfx.audio.hash | ||
| noise_triangle_sfx.png | ||
| palette_and_background.audio.hash | ||
| palette_and_background.png | ||
| platformer.audio.hash | ||
| platformer.png | ||
| pong.audio.hash | ||
| pong.png | ||
| scanline_split.audio.hash | ||
| scanline_split.png | ||
| sfx_pitch_envelope.audio.hash | ||
| sfx_pitch_envelope.png | ||
| sha256.audio.hash | ||
| sha256.png | ||
| sprite_flicker_demo.audio.hash | ||
| sprite_flicker_demo.png | ||
| sprites_and_palettes.audio.hash | ||
| sprites_and_palettes.png | ||
| state_machine.audio.hash | ||
| state_machine.png | ||
| structs_enums_for.audio.hash | ||
| structs_enums_for.png | ||
| two_player.audio.hash | ||
| two_player.png | ||
| uxrom_banked.audio.hash | ||
| uxrom_banked.png | ||
| uxrom_banked_to_banked.audio.hash | ||
| uxrom_banked_to_banked.png | ||
| uxrom_user_banked.audio.hash | ||
| uxrom_user_banked.png | ||
| war.audio.hash | ||
| war.png | ||
