From 9ab731bf668005f196fe5d0020cedd08629e686d Mon Sep 17 00:00:00 2001
From: Chris Tate <chris@ctate.dev>
Date: Fri, 23 Oct 2026 19:42:52 -0500
Subject: [PATCH] Version while loops only for accesses at their counters

A while loop over typed arrays also versioned when its only checks were
thread-owned receivers or static indices. A worker's job loop such as
`while ((job = Atomics.load(next, 0)) < count) { ...; run(job) }` then
got a second copy whose guard fails whenever the array is shared, and
the doubled call kept the job function from being inlined. A while loop
now versions only when it has an access at one of its counters. Other
while loops compile as they did before they could version.
---
 .../src/backend/llvm/bytes-loop-versions.test.ts     | 12 ++++++++++--
 .../compiler/src/backend/llvm/bytes-loop-versions.ts |  5 +++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/packages/compiler/src/backend/llvm/bytes-loop-versions.test.ts b/packages/compiler/src/backend/llvm/bytes-loop-versions.test.ts
index de71a6ef0..aef39ef75 100644
--- a/packages/compiler/src/backend/llvm/bytes-loop-versions.test.ts
+++ b/packages/compiler/src/backend/llvm/bytes-loop-versions.test.ts
@@ -385,7 +385,10 @@ test("while loop counters below a bound version their accesses", () => {
   ]);
   const declared = (loop: IrStmt): IrFunction =>
     fn([{ kind: "varDecl", localId: "i", init: ref("k"), loc }, loop]);
-  const versionOf = (loop: IrStmt & { kind: "while" }): BytesLoopVersion | null => {
+  const versionOf = (
+    loop: IrStmt & { kind: "while" },
+    workers = false,
+  ): BytesLoopVersion | null => {
     const f = declared(loop);
     const ranges = analyzeIntegerRanges(f);
     return matchBytesLoopVersion(loop, null, {
@@ -396,7 +399,7 @@ test("while loop counters below a bound version their accesses", () => {
       initialized: findInitializedByteLoopBindings(f).get(loop) ?? new Set(),
       proven: new Set(),
       scalarStrings: new Set(),
-      workers: false,
+      workers,
       owned: new Set(),
     });
   };
@@ -413,6 +416,11 @@ test("while loop counters below a bound version their accesses", () => {
   // An access after the counter advances in the same pass stays checked.
   const advanced = whileLoop([step, set(ref("out", f64s), ref("i"), num(0))]);
   expect(versionOf(advanced)).toBeNull();
+  // In a worker program, a while loop versions for its counter's accesses,
+  // and not for thread-owned receivers alone.
+  expect(versionOf(copy, true)!.ownedReceivers).toHaveLength(2);
+  const job = whileLoop([set(ref("out", f64s), ref("k"), get(ref("src", f64s), ref("k"))), step]);
+  expect(versionOf(job, true)).toBeNull();
   const mod: IrModule = {
     irVersion: 17,
     sourceFile: loc.file,
diff --git a/packages/compiler/src/backend/llvm/bytes-loop-versions.ts b/packages/compiler/src/backend/llvm/bytes-loop-versions.ts
index 2013d03e4..1b51deee1 100644
--- a/packages/compiler/src/backend/llvm/bytes-loop-versions.ts
+++ b/packages/compiler/src/backend/llvm/bytes-loop-versions.ts
@@ -581,6 +581,11 @@ export function matchBytesLoopVersion(
     pairedKept.length === 0
   )
     return null;
+  // A while loop versions only for accesses at its counters. Its other
+  // checks (thread-owned receivers, static indices) save a test or two per
+  // pass, while a second copy of its body doubles the calls it makes, which
+  // can keep a worker's job loop from inlining the function that runs a job.
+  if (loop.kind === "while" && boundedKept.length === 0) return null;
   const bounds = new Set<Node>();
   const ownedNodes = new Set<Node>();
   const used = new Set<number>();