From 6b67f597a6bc286fdf716c6840ece0c56997aba1 Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Tue, 14 Feb 2023 09:33:23 -0800
Subject: [PATCH] Capturing a frozen value is a Read

If a value is known to be frozen (or potentially frozen), then it doesn't need
to be considered 'captured' since no mutation can occur via aliasing.
---
 .../src/Inference/InferReferenceEffects.ts    |   9 +-
 ...s-dep-and-redeclare-maybe-frozen.expect.md | 127 ++++++++++++++++++
 ...iable-as-dep-and-redeclare-maybe-frozen.js |  35 +++++
 ...me-variable-as-dep-and-redeclare.expect.md | 124 +++++++++++++++++
 .../hir/same-variable-as-dep-and-redeclare.js |  35 +++++
 5 files changed, 329 insertions(+), 1 deletion(-)
 create mode 100644 compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare-maybe-frozen.expect.md
 create mode 100644 compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare-maybe-frozen.js
 create mode 100644 compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare.expect.md
 create mode 100644 compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare.js

diff --git a/compiler/forget/src/Inference/InferReferenceEffects.ts b/compiler/forget/src/Inference/InferReferenceEffects.ts
index bf64963d09..29c5a00099 100644
--- a/compiler/forget/src/Inference/InferReferenceEffects.ts
+++ b/compiler/forget/src/Inference/InferReferenceEffects.ts
@@ -308,7 +308,14 @@ class Environment {
         break;
       }
       case Effect.Capture: {
-        effect = Effect.Capture;
+        if (
+          valueKind === ValueKind.Frozen ||
+          valueKind === ValueKind.MaybeFrozen
+        ) {
+          effect = Effect.Read;
+        } else {
+          effect = Effect.Capture;
+        }
         break;
       }
       case Effect.Read: {
diff --git a/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare-maybe-frozen.expect.md b/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare-maybe-frozen.expect.md
new file mode 100644
index 0000000000..50fae20d8d
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare-maybe-frozen.expect.md
@@ -0,0 +1,127 @@
+
+## Input
+
+```javascript
+// note: comments are for the ideal scopes, not what is currently
+// emitted
+function foo(props) {
+  // scope 0: deps=[props.a] decl=[x] reassign=none
+  let x = [];
+  x.push(props.a);
+
+  // scope 1: deps=[x] decl=[header] reassign=none
+  const header = props.showHeader ? <div>{x}</div> : null;
+
+  // scope 2:
+  // deps=[x, props.b, props.c]
+  // decl=none
+  // reassign=[x]
+  const y = [x]; // y depends on the earlier x
+  x = []; // x reassigned
+  y.push(props.b); // interleaved mutation of x/y
+  x.push(props.c); // interleaved mutation
+
+  // scope 3 ...
+  const content = (
+    <div>
+      {x}
+      {y}
+    </div>
+  );
+
+  // scope 4 ...
+  return (
+    <>
+      {header}
+      {content}
+    </>
+  );
+}
+
+```
+
+## Code
+
+```javascript
+// note: comments are for the ideal scopes, not what is currently
+// emitted
+function foo(props) {
+  const $ = React.unstable_useMemoCache();
+  const c_0 = $[0] !== props.a;
+  let x;
+  if (c_0) {
+    x = [];
+    x.push(props.a);
+    $[0] = props.a;
+    $[1] = x;
+  } else {
+    x = $[1];
+  }
+  const c_2 = $[2] !== props;
+  const c_3 = $[3] !== x;
+  let t0;
+  if (c_2 || c_3) {
+    t0 = props.showHeader ? <div>{x}</div> : null;
+    $[2] = props;
+    $[3] = x;
+    $[4] = t0;
+  } else {
+    t0 = $[4];
+  }
+  const header = t0;
+  const c_5 = $[5] !== x;
+  const c_6 = $[6] !== props.b;
+  const c_7 = $[7] !== props.c;
+  let x$0;
+  let y;
+  if (c_5 || c_6 || c_7) {
+    y = [x];
+    x$0 = [];
+    y.push(props.b);
+    x$0.push(props.c);
+    $[5] = x;
+    $[6] = props.b;
+    $[7] = props.c;
+    $[8] = x$0;
+    $[9] = y;
+  } else {
+    x$0 = $[8];
+    y = $[9];
+  }
+  const c_10 = $[10] !== x$0;
+  const c_11 = $[11] !== y;
+  let content;
+  if (c_10 || c_11) {
+    content = (
+      <div>
+        {x$0}
+        {y}
+      </div>
+    );
+    $[10] = x$0;
+    $[11] = y;
+    $[12] = content;
+  } else {
+    content = $[12];
+  }
+  const c_13 = $[13] !== header;
+  const c_14 = $[14] !== content;
+  let t1;
+  if (c_13 || c_14) {
+    t1 = (
+      <>
+        {header}
+        {content}
+      </>
+    );
+    $[13] = header;
+    $[14] = content;
+    $[15] = t1;
+  } else {
+    t1 = $[15];
+  }
+  return t1;
+}
+
+```
+      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare-maybe-frozen.js b/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare-maybe-frozen.js
new file mode 100644
index 0000000000..67149fb3f3
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare-maybe-frozen.js
@@ -0,0 +1,35 @@
+// note: comments are for the ideal scopes, not what is currently
+// emitted
+function foo(props) {
+  // scope 0: deps=[props.a] decl=[x] reassign=none
+  let x = [];
+  x.push(props.a);
+
+  // scope 1: deps=[x] decl=[header] reassign=none
+  const header = props.showHeader ? <div>{x}</div> : null;
+
+  // scope 2:
+  // deps=[x, props.b, props.c]
+  // decl=none
+  // reassign=[x]
+  const y = [x]; // y depends on the earlier x
+  x = []; // x reassigned
+  y.push(props.b); // interleaved mutation of x/y
+  x.push(props.c); // interleaved mutation
+
+  // scope 3 ...
+  const content = (
+    <div>
+      {x}
+      {y}
+    </div>
+  );
+
+  // scope 4 ...
+  return (
+    <>
+      {header}
+      {content}
+    </>
+  );
+}
diff --git a/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare.expect.md b/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare.expect.md
new file mode 100644
index 0000000000..f975bb3535
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare.expect.md
@@ -0,0 +1,124 @@
+
+## Input
+
+```javascript
+// note: comments are for the ideal scopes, not what is currently
+// emitted
+function foo(props) {
+  // scope 0: deps=[props.a] decl=[x] reassign=none
+  let x = [];
+  x.push(props.a);
+
+  // scope 1: deps=[x] decl=[header] reassign=none
+  const header = <div>{x}</div>;
+
+  // scope 2:
+  // deps=[x, props.b, props.c]
+  // decl=none
+  // reassign=[x]
+  const y = [x]; // y depends on the earlier x
+  x = []; // x reassigned
+  y.push(props.b); // interleaved mutation of x/y
+  x.push(props.c); // interleaved mutation
+
+  // scope 3 ...
+  const content = (
+    <div>
+      {x}
+      {y}
+    </div>
+  );
+
+  // scope 4 ...
+  return (
+    <>
+      {header}
+      {content}
+    </>
+  );
+}
+
+```
+
+## Code
+
+```javascript
+// note: comments are for the ideal scopes, not what is currently
+// emitted
+function foo(props) {
+  const $ = React.unstable_useMemoCache();
+  const c_0 = $[0] !== props.a;
+  let x;
+  if (c_0) {
+    x = [];
+    x.push(props.a);
+    $[0] = props.a;
+    $[1] = x;
+  } else {
+    x = $[1];
+  }
+  const c_2 = $[2] !== x;
+  let header;
+  if (c_2) {
+    header = <div>{x}</div>;
+    $[2] = x;
+    $[3] = header;
+  } else {
+    header = $[3];
+  }
+  const c_4 = $[4] !== x;
+  const c_5 = $[5] !== props.b;
+  const c_6 = $[6] !== props.c;
+  let x$0;
+  let y;
+  if (c_4 || c_5 || c_6) {
+    y = [x];
+    x$0 = [];
+    y.push(props.b);
+    x$0.push(props.c);
+    $[4] = x;
+    $[5] = props.b;
+    $[6] = props.c;
+    $[7] = x$0;
+    $[8] = y;
+  } else {
+    x$0 = $[7];
+    y = $[8];
+  }
+  const c_9 = $[9] !== x$0;
+  const c_10 = $[10] !== y;
+  let content;
+  if (c_9 || c_10) {
+    content = (
+      <div>
+        {x$0}
+        {y}
+      </div>
+    );
+    $[9] = x$0;
+    $[10] = y;
+    $[11] = content;
+  } else {
+    content = $[11];
+  }
+  const c_12 = $[12] !== header;
+  const c_13 = $[13] !== content;
+  let t0;
+  if (c_12 || c_13) {
+    t0 = (
+      <>
+        {header}
+        {content}
+      </>
+    );
+    $[12] = header;
+    $[13] = content;
+    $[14] = t0;
+  } else {
+    t0 = $[14];
+  }
+  return t0;
+}
+
+```
+      
\ No newline at end of file
diff --git a/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare.js b/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare.js
new file mode 100644
index 0000000000..6d8c5cb3f9
--- /dev/null
+++ b/compiler/forget/src/__tests__/fixtures/hir/same-variable-as-dep-and-redeclare.js
@@ -0,0 +1,35 @@
+// note: comments are for the ideal scopes, not what is currently
+// emitted
+function foo(props) {
+  // scope 0: deps=[props.a] decl=[x] reassign=none
+  let x = [];
+  x.push(props.a);
+
+  // scope 1: deps=[x] decl=[header] reassign=none
+  const header = <div>{x}</div>;
+
+  // scope 2:
+  // deps=[x, props.b, props.c]
+  // decl=none
+  // reassign=[x]
+  const y = [x]; // y depends on the earlier x
+  x = []; // x reassigned
+  y.push(props.b); // interleaved mutation of x/y
+  x.push(props.c); // interleaved mutation
+
+  // scope 3 ...
+  const content = (
+    <div>
+      {x}
+      {y}
+    </div>
+  );
+
+  // scope 4 ...
+  return (
+    <>
+      {header}
+      {content}
+    </>
+  );
+}