[maglev] Only create phis for contexts of resumable loops

We need them there due to how they are restored on resume, but don't need them at all for other loops.

Bug: v8:7700
Change-Id: I28a13ccf05d4fcd7bcf5fb8abef4dedd64f990f4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4197096
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Auto-Submit: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#85498}

src/maglev/maglev-interpreter-frame-state.cc

@@ -106,9 +106,14 @@ MergePointInterpreterFrameState* MergePointInterpreterFrameState::NewForLoop(
         }
         ++i;
       });
-  // TODO(v8:7700): Add contexts into assignment analysis.
-  frame_state.context(info) = state->NewLoopPhi(
-      info.zone(), interpreter::Register::current_context(), merge_offset);
+  frame_state.context(info) = nullptr;
+  if (state->is_resumable_loop_) {
+    // While contexts are always the same at specific locations, resumable loops
+    // do have different nodes to set the context across resume points. Create a
+    // phi for them.
+    frame_state.context(info) = state->NewLoopPhi(
+        info.zone(), interpreter::Register::current_context(), merge_offset);
+  }
   frame_state.ForEachLocal(
       info, [&](ValueNode*& entry, interpreter::Register reg) {
         entry = nullptr;

test/mjsunit/maglev/resumable-loop-context.js

@@ -0,0 +1,19 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax --maglev
+
+async function __f_20() {
+  try {
+    for (let __v_58 = 0; __v_58 < 8; __v_58++) {
+    }
+  } catch (e) {}
+    for (let __v_59 = 1; __v_59 < 1337; __v_59++) {
+      function* __f_21() {}
+      const __v_66 = __f_21();
+      const __v_69 = await "-4294967296";
+    }
+}
+
+__f_20();