1	# performance/drop_in_bang: a `!` call of a definition that returns Unit: Base's Image.drop, Image.free
2	# or Image.sink, or a definition of the program declared `-> Unit`. A pure definition that returns Unit
3	# does nothing but free what it receives, and a GPU frees slower than its CPU.
4	# Heuristics: measured on a discrete GPU (CUDA), 30 frames that each dropped a 1M-leaf image with
5	# `Image.drop!` took 1.55 s, against 0.10 s with `Image.drop` (0.104 s against 0.094 s with `--gpu off`).
6	# "bend guide shaders" measured freeing Bend's slash boss scene in a bang at 12.9 ms a frame, against 8.0
7	# ms, on an Apple M-series GPU, whose memory is unified: the GPU loses on both kinds of memory. The JS
8	# lane has no GPU. A return type written another way (an alias of Unit) is not known.
9	import Base
10	import bend-lint-api@0.2.0.0/linter/lint.bend as Lint
11	import bend-lint-api@0.2.0.0/shared/names.bend as Names
12	import ./gpu_fit.bend as GpuFit
13	
14	# Types
15	# =====
16	
17	# What judging a file's calls reads: the program's definitions, by the name the check gives them, and where the file
18	# writes `!(`.
19	type Program is Data:
20	  Program{defs: Map<&2, Maybe<&2, Lint.Def>>, bangs: List<&2, U32>}
21	
22	# Functions
23	# =========
24	def message(callee: String) -> String:
25	  callee
26	    ++ "! only frees what it receives, as it returns Unit, and a GPU frees slower than its CPU. GPU: measured 15x slower than without the `!` on a discrete GPU (CUDA), dropping a 1M-leaf image; with unified memory (Apple M-series), freeing a scene in a bang made a frame 12.9 ms, against 8.0 ms (\"bend guide shaders\"). CPU (`--gpu off`): 10% slower. JS: no GPU, so no change. Confidence: high, as a GPU does not speed up freeing. Remove the `!`; to drop the last frame, let the next frame's fork tree drop it, a quadrant per tile (\"bend guide shaders\"). If a timing shows the `!` faster here, expect this finding."
27	
28	# The finding about an application below `path`, if it is a `!` call that only frees.
29	def visit(
30	  +program: Program,
31	  +path: List<&2, Lint.Above>,
32	  +node: Lint.Node
33	) -> List<&2, Lint.Finding>:
34	  match program node:
35	    case Program{
36	      defs,
37	      bangs
38	    } Lint.Node{
39	      Lint.Application{},
40	      n,
41	      span,
42	      Con{Lint.Node{Lint.Reference{+t}, callee, Some{Lint.Span{p, beg, end}}, k, f}, args},
43	      facts
44	    }:
45	      Lint.finding(
46	        Lint.Warning{},
47	        List.contains(
48	          ~U32,
49	          ~U32.is_eq,
50	          bangs,
51	          end
52	        )
53	          && GpuFit.is_drop(Names.find(Lint.Def, defs, t), t),
54	        span,
55	        message(callee)
56	      )
57	    case _ _:
58	      []
59	
60	def run(+here: Lint.Here) -> Lint.Ask(List<&2, Lint.Finding>):
61	  Lint.done(
62	    Lint.visit(
63	      ~Program,
64	      ~Lint.Finding,
65	      ~visit,
66	      Program{
67	        Lint.Program.defs(Lint.Here.sources(here), Map.new(&2, Maybe<&2, Lint.Def>)),
68	        GpuFit.bangs(Lint.Here.text(here), 0, [])
69	      },
70	      Lint.Here.nodes(here)
71	    )
72	  )
73	
74	def rule() -> Lint.Rule:
75	  Lint.Rule{Lint.Needs{False{}, False{}}, [], Lint.OnFile{run}}