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LowLevelRegisters tuple order and drop unused register helpers #21605

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2718522
Fix LowLevelRegisters tuple order and drop unused register helpers
NullVoxPopuli Sep 9, 2026
7186100
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NullVoxPopuli Sep 21, 2026
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18 changes: 1 addition & 17 deletions packages/@glimmer/runtime/lib/vm/low-level.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -23,23 +23,7 @@ import type { VM } from './append';
import '../bootstrap';
import { APPEND_OPCODES } from '../opcodes';

export type LowLevelRegisters = [$pc: number, $ra: number, $sp: number, $fp: number];

export function initializeRegisters(): LowLevelRegisters {
return [0, -1, 0, 0];
}

export function restoreRegisters(pc: number, sp: number): LowLevelRegisters {
return [pc, -1, sp, 0];
}

export function initializeRegistersWithSP(sp: number): LowLevelRegisters {
return [0, -1, sp, 0];
}

export function initializeRegistersWithPC(pc: number): LowLevelRegisters {
return [pc, -1, 0, 0];
}
export type LowLevelRegisters = [$pc: number, $ra: number, $fp: number, $sp: number];

@NullVoxPopuli NullVoxPopuli Sep 21, 2026

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labels on an array type don't materr all that much, but they didn't originally agree with the index-order in lib/vm/stack (even though the original type matched what the removed (unused) helpers were doin'

the source of truth for what these labeled indicies are: vm/lib/register.ts (also imported in lib/vm/stack)

pc = 0
ra = 1
fp = 2
sp = 3

(so the code on the left was always wrong) 🙈


export interface VmStack {
readonly registers: LowLevelRegisters;
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21 changes: 3 additions & 18 deletions packages/@glimmer/runtime/lib/vm/stack.ts
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Original file line number Diff line number Diff line change
@@ -1,11 +1,9 @@
import assert from '@glimmer/debug-util/lib/assert';
import { LOCAL_DEBUG } from '@glimmer/local-debug-flags';
import { $fp, $pc, $sp } from '@glimmer/vm/lib/registers';
import { $fp, $sp } from '@glimmer/vm/lib/registers';

import type { LowLevelRegisters } from './low-level';

import { initializeRegistersWithSP } from './low-level';

export interface EvaluationStack {
readonly registers: LowLevelRegisters;

Expand All @@ -25,15 +23,10 @@ export interface EvaluationStack {

export default class EvaluationStackImpl implements EvaluationStack {
static restore(snapshot: unknown[], pc: number): EvaluationStackImpl {
const stack = new this(snapshot.slice(), initializeRegistersWithSP(snapshot.length - 1));

assert(typeof pc === 'number', 'pc is a number');

stack.registers[$pc] = pc;
stack.registers[$sp] = snapshot.length - 1;
stack.registers[$fp] = -1;

return stack;
// [$pc, $ra, $fp, $sp]
return new this(snapshot.slice(), [pc, -1, -1, snapshot.length - 1]);
}

readonly registers: LowLevelRegisters;
Expand Down Expand Up @@ -100,12 +93,4 @@ export default class EvaluationStackImpl implements EvaluationStack {
}

declare snapshot?: (this: EvaluationStackImpl) => unknown[];

static {
if (LOCAL_DEBUG) {
EvaluationStackImpl.prototype.snapshot = function () {
return this.stack.slice(this.registers[$fp], this.registers[$sp] + 1);
};
}
}
}
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