feat!: Grain implementation of memory allocator #530

ospencer · 2021-02-13T17:48:22Z

Grain Implementation of `malloc`/`free`

This is a breaking change, as some runtime libraries were moved around.

This PR re-implements the Grain memory allocator in Grain. The allocator itself is nearly identical to the old version, so the interesting bits are the changes to how the Grain runtime works, and that effect on the new runtime libraries.

Compilation Modes

The Grain compiler sports two new compilation modes—Runtime and MemoryAllocation. The "normal" compilation mode is called Normal. Runtime mode and MemoryAllocation mode can be enabled for a module by adding the /* compilation-mode: runtime */ or /* compilation-mode: malloc */ block comments at the start of the file.

`Runtime` Mode

The essence behind Runtime mode is that garbage collection/memory allocation isn't set up yet (and that's probably what's currently being compiled!). As such, modules in Runtime mode do not implicitly depend on Pervasives or have garbage collection enabled. For any allocations that need to be done (just closures), that data exists in the runtime heap—Grain now reserves 4096 bytes of memory for the runtime. After some testing, the runtime currently uses 392 bytes of memory, so this amount should give us some breathing room.

`MemoryAllocation` Mode

This mode is the same as Runtime mode, with the addition that the pointer to the runtime heap exists in this module. (As such, Runtime mode imports that pointer from here.)

`Normal` Mode

This is the mode that we already know and love, but as a quick refresher—modules compiled in this mode implicitly depend on Pervasives and have their memory managed via the GC.

Runtime Libraries

There's a new runtime folder in stdlib where the runtime things will live, i.e. print, toString, numbers, etc.
The WasmI32/WasmI64/WasmF32/WasmF64 libraries have been moved from the unsafe stdlib directory to runtime/unsafe. Because malloc.gr needs to depend on wasmi32.gr and it depended on Pervasives for print, the conversion and print functionalities have been moved to runtime/unsafe/conv.gr and runtime/unsafe/utils.gr, which is the breaking change.
Additionally, there's now also runtime/debug.gr, where runtime debugging utilities will live (and I even got to use it to debug malloc!).

JS Runtime

The JS runtime got to be cleaned up a bit with no more need to manually load the memory allocator since the allocator is now just a regular Grain module that is depended on in the normal way.

ospencer · 2021-02-13T17:49:32Z

compiler/src/parsing/lexer.mll

@@ -58,7 +58,7 @@
  let consume_comments () =
    let out_comments = !comments in
    comments := [];
-    out_comments
+    List.rev(out_comments)


Turns out all of our comments were in reverse order.

phated

Things I saw or was confused by!

compiler/src/codegen/compcore.re

stdlib/runtime/debug.gr

stdlib/runtime/malloc.gr

stdlib/runtime/unsafe/utils.gr

phated

Looking great! Thanks for entertaining my questions! 🙇

peblair

This is awesome! Please review my comments before merging, but this looks great! 🚀

peblair · 2021-03-07T11:44:00Z

compiler/src/codegen/compcore.re


-let round_allocation_size = (num_words: int): int => round_up(num_words, 4);
+let heap_allocate = (wasm_mod, env, num_words: int) =>


I kind of wish we used an ADT here which was something like this:

type allocation_size = | AllocWords(int) | AllocBytes(int)

Even if we only have AllocWords as the only variant, I feel like it'd be more expressive/readable/"safe":tm:, since it will be clear at the use sites that the number we're passing into heap_allocate represents words rather than bytes.

Could be a good future change, yeah.

peblair · 2021-03-07T11:47:16Z

compiler/src/codegen/mashtree.re

@@ -429,7 +429,7 @@ and block = list(instr);
 [@deriving sexp]
 type import_type =
  | MFuncImport(list(asmtype), list(asmtype))
-  | MGlobalImport(asmtype);
+  | MGlobalImport(asmtype, bool);


We should consider documenting these fields. Perhaps we should try to add documentation to an ADT definition whenever we update it?

In general, I suppose so, yeah. This one sorta makes sense because globals went from always being immutable to optionally being mutable. I think in general we could prefer the record-type variants since those are self-documenting.

peblair · 2021-03-07T11:50:10Z

compiler/src/parsing/lexer.mll

@@ -58,7 +58,7 @@
  let consume_comments () =
    let out_comments = !comments in
    comments := [];
-    out_comments
+    List.rev(out_comments)


peblair · 2021-03-07T11:57:02Z

compiler/src/typed/env.re


-let set_unit = ((name, source)) => current_unit := (name, source);
+let current_unit = ref(("", "", Normal));


This has inspired me to open #547 .

peblair · 2021-03-07T11:59:26Z

runtime/src/core/memory.js

+      "GRAIN$EXPORT$malloc"
+    ).value;
+    return this._runtime.memoryManager.requiredExport("malloc")(
+      closure,


@ospencer To make sure I understand, this is needed because we now need to follow the Grain calling convention, yes?

ospencer requested a review from a team February 13, 2021 17:48

ospencer self-assigned this Feb 13, 2021

ospencer commented Feb 13, 2021

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ospencer changed the title ~~chore!: Grain implementation of memory allocator~~ feat!: Grain implementation of memory allocator Feb 15, 2021

ospencer force-pushed the grain-runtime branch from 571567c to 28d6e93 Compare February 15, 2021 17:58

feat!: Grain implementation of memory allocator

375b283

ospencer force-pushed the grain-runtime branch from 28d6e93 to 375b283 Compare February 15, 2021 17:59

phated reviewed Feb 22, 2021

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PR feedback

42fed17

peblair self-requested a review February 25, 2021 17:16

rename utils.gr -> printWasm.gr

ad3c6bb

phated approved these changes Mar 6, 2021

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peblair approved these changes Mar 7, 2021

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ospencer merged commit fd8faaa into main Mar 7, 2021

ospencer deleted the grain-runtime branch March 7, 2021 14:36

phated mentioned this pull request Apr 19, 2021

chore: release testing-release #595

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github-actions bot mentioned this pull request Apr 20, 2021

chore: release main #607

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github-actions bot mentioned this pull request May 31, 2022

chore: release main #1292

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github-actions bot mentioned this pull request Jul 25, 2022

chore: release main spotandjake/grain#1

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feat!: Grain implementation of memory allocator #530

feat!: Grain implementation of memory allocator #530

ospencer commented Feb 13, 2021

ospencer Feb 13, 2021

phated Feb 22, 2021

peblair Mar 7, 2021

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ospencer Mar 7, 2021


		let round_allocation_size = (num_words: int): int => round_up(num_words, 4);
		let heap_allocate = (wasm_mod, env, num_words: int) =>


		let set_unit = ((name, source)) => current_unit := (name, source);
		let current_unit = ref(("", "", Normal));

feat!: Grain implementation of memory allocator #530

feat!: Grain implementation of memory allocator #530

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ospencer commented Feb 13, 2021

Grain Implementation of malloc/free

Compilation Modes

Runtime Mode

MemoryAllocation Mode

Normal Mode

Runtime Libraries

JS Runtime

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Grain Implementation of `malloc`/`free`

`Runtime` Mode

`MemoryAllocation` Mode

`Normal` Mode