From 7b91c5fe5c4ce396c158091327ede08188ec4a4c Mon Sep 17 00:00:00 2001
From: Malte Ubl <malte@vercel.com>
Date: Tue, 27 Oct 2026 00:53:10 -0700
Subject: [PATCH] Plan record views before any host copies the shape host

The walkers take a narrower host type than the emitter's shape host; in
the self-hosted compiler that conversion copies the host, so a plan
assigned afterwards never reached them and the native emitter left view
guards out. The plan is now made before the copies, and arena shapes leave
its shared target set once arenas are planned.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 packages/compiler/src/backend/llvm/emitter.ts | 33 +++++++++++++------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/packages/compiler/src/backend/llvm/emitter.ts b/packages/compiler/src/backend/llvm/emitter.ts
index f2998db785..f2025bdf2d 100644
--- a/packages/compiler/src/backend/llvm/emitter.ts
+++ b/packages/compiler/src/backend/llvm/emitter.ts
@@ -1397,6 +1397,8 @@ export class LlEmitter {
   readonly dyn: LlDyn;
   /** Explicit callback boundary for standalone layout and walker stages. */
   readonly shapeHost: DynHost;
+  /** The record view plan's target set (record-views.ts), shared by reference. */
+  private recordViewTargets: Set<string> | null = null;
   /** External declarations, in first-use order. */
   readonly decls = new Set<string>();
   /** Declared functions referenced as values: each needs an env-signature
@@ -2402,6 +2404,20 @@ export class LlEmitter {
         }
       }
     }
+    // Planned before any host copies the shape host (record-views.ts).
+    {
+      const views = planRecordViews(mod, {
+        traced: (id) => this.tracedShapes.has(`record:${id}`),
+        // A tagged shape's values share field reads with the other arms of
+        // its shape union.
+        excluded: (id) =>
+          this.nullableUnions.shapeNumber(id) !== 0 ||
+          this.publishedTypes?.recordGuarded(id) === true ||
+          mod.workers === true,
+      });
+      this.shapeHost.recordViews = views;
+      this.recordViewTargets = views.targets as Set<string>;
+    }
     this.walkers = new LlWalkers(this.shapeHost);
     this.dyn = new LlDyn(this.shapeHost);
     for (const g of mod.globals ?? []) {
@@ -2524,16 +2540,13 @@ export class LlEmitter {
         this.shapeHost.arenasClosed = this.arenas.allClosed;
       }
     }
-    this.shapeHost.recordViews = planRecordViews(mod, {
-      traced: (id) => this.tracedShapes.has(`record:${id}`),
-      // A tagged shape's values share field reads with the other arms of
-      // its shape union, which do not carry view words.
-      excluded: (id) =>
-        this.nullableUnions.shapeNumber(id) !== 0 ||
-        this.shapeHost.arenaShapes?.has(id) === true ||
-        this.publishedTypes?.recordGuarded(id) === true ||
-        mod.workers === true,
-    });
+    // Arena shapes are known only now; the plan's target set is shared by
+    // every host that copied the shape host, so dropping them here reaches
+    // all of them.
+    const arenaShapes = this.shapeHost.arenaShapes;
+    const viewTargets = this.recordViewTargets;
+    if (arenaShapes !== undefined && viewTargets !== null)
+      for (const id of arenaShapes) viewTargets.delete(id);
     for (const [name, rec] of RUNTIME_ERROR_CLASSES) {
       const meta = this.classMeta.get(name);
       if (!meta) break; // hand-written IR without the builtin defs: no stamps