From 55fdcf87bdab39853252369ad0dc68cb88a15102 Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Wed, 12 Jun 2024 14:49:13 -0700
Subject: [PATCH] [compiler] Fix merging of queued states in
 InferReferenceEffects

Fixes a bug found by mofeiZ in #29878. When we merge queued states, if the new state does not introduce changes relative to the queued state we should use the queued state, not the new state.

ghstack-source-id: c59f69de15fa89bd1ed049d0a7d221651577ae34
Pull Request resolved: https://github.com/facebook/react/pull/29879
---
 .../src/Inference/InferReferenceEffects.ts    |  4 +-
 .../compiler/phi-reference-effects.expect.md  | 61 +++++++++++++++++++
 .../compiler/phi-reference-effects.ts         | 19 ++++++
 3 files changed, 82 insertions(+), 2 deletions(-)
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/phi-reference-effects.expect.md
 create mode 100644 compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/phi-reference-effects.ts

diff --git a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferReferenceEffects.ts b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferReferenceEffects.ts
index 619d1d90ff..ee2ad1a7de 100644
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferReferenceEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferReferenceEffects.ts
@@ -201,7 +201,7 @@ export default function inferReferenceEffects(
     let queuedState = queuedStates.get(blockId);
     if (queuedState != null) {
       // merge the queued states for this block
-      state = queuedState.merge(state) ?? state;
+      state = queuedState.merge(state) ?? queuedState;
       queuedStates.set(blockId, state);
     } else {
       /*
@@ -765,7 +765,7 @@ class InferenceState {
       result.values[id] = { kind, value: printMixedHIR(value) };
     }
     for (const [variable, values] of this.#variables) {
-      result.variables[variable] = [...values].map(identify);
+      result.variables[`$${variable}`] = [...values].map(identify);
     }
     return result;
   }
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/phi-reference-effects.expect.md b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/phi-reference-effects.expect.md
new file mode 100644
index 0000000000..bef1d7b836
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/phi-reference-effects.expect.md
@@ -0,0 +1,61 @@
+
+## Input
+
+```javascript
+import { arrayPush } from "shared-runtime";
+
+function Foo(cond) {
+  let x = null;
+  if (cond) {
+    x = [];
+  } else {
+  }
+  // Here, x = phi(x$null, x$[]) should receive a ValueKind of Mutable
+  arrayPush(x, 2);
+
+  return x;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Foo,
+  params: [{ cond: true }],
+  sequentialRenders: [{ cond: true }, { cond: true }],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime";
+import { arrayPush } from "shared-runtime";
+
+function Foo(cond) {
+  const $ = _c(2);
+  let x;
+  if ($[0] !== cond) {
+    x = null;
+    if (cond) {
+      x = [];
+    }
+
+    arrayPush(x, 2);
+    $[0] = cond;
+    $[1] = x;
+  } else {
+    x = $[1];
+  }
+  return x;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Foo,
+  params: [{ cond: true }],
+  sequentialRenders: [{ cond: true }, { cond: true }],
+};
+
+```
+      
+### Eval output
+(kind: ok) [2]
+[2]
\ No newline at end of file
diff --git a/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/phi-reference-effects.ts b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/phi-reference-effects.ts
new file mode 100644
index 0000000000..092791d586
--- /dev/null
+++ b/compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/phi-reference-effects.ts
@@ -0,0 +1,19 @@
+import { arrayPush } from "shared-runtime";
+
+function Foo(cond) {
+  let x = null;
+  if (cond) {
+    x = [];
+  } else {
+  }
+  // Here, x = phi(x$null, x$[]) should receive a ValueKind of Mutable
+  arrayPush(x, 2);
+
+  return x;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Foo,
+  params: [{ cond: true }],
+  sequentialRenders: [{ cond: true }, { cond: true }],
+};