[HIR] Nonnullable block fallthroughs

ghstack-source-id: 6f24b60056c741e5d4e9836f91bc4fce0f9e8fdd
Pull Request resolved: https://github.com/facebook/react-forget/pull/2865

compiler/packages/babel-plugin-react-forget/src/HIR/HIR.ts

@@ -362,6 +362,8 @@ export type Terminal =
   | TryTerminal
   | ReactiveScopeTerminal;
 
+export type TerminalWithFallthrough = Terminal & { fallthrough: BlockId };
+
 function _staticInvariantTerminalHasLocation(
   terminal: Terminal
 ): SourceLocation {
@@ -376,6 +378,13 @@ function _staticInvariantTerminalHasInstructionId(
   return terminal.id;
 }
 
+function _staticInvariantTerminalHasFallthrough(
+  terminal: Terminal
+): BlockId | never | undefined {
+  // If this fails, it is because a variant of Terminal is missing a fallthrough annotation
+  return terminal.fallthrough;
+}
+
 /*
  * Terminal nodes allowed for a value block
  * A terminal that couldn't be lowered correctly.
@@ -384,6 +393,7 @@ export type UnsupportedTerminal = {
   kind: "unsupported";
   id: InstructionId;
   loc: SourceLocation;
+  fallthrough?: never;
 };
 
 /**
@@ -395,6 +405,7 @@ export type UnreachableTerminal = {
   kind: "unreachable";
   id: InstructionId;
   loc: SourceLocation;
+  fallthrough?: never;
 };
 
 export type ThrowTerminal = {
@@ -402,6 +413,7 @@ export type ThrowTerminal = {
   value: Place;
   id: InstructionId;
   loc: SourceLocation;
+  fallthrough?: never;
 };
 export type Case = { test: Place | null; block: BlockId };
 
@@ -410,6 +422,7 @@ export type ReturnTerminal = {
   loc: SourceLocation;
   value: Place;
   id: InstructionId;
+  fallthrough?: never;
 };
 
 export type GotoTerminal = {
@@ -418,6 +431,7 @@ export type GotoTerminal = {
   variant: GotoVariant;
   id: InstructionId;
   loc: SourceLocation;
+  fallthrough?: never;
 };
 
 export enum GotoVariant {
@@ -431,7 +445,7 @@ export type IfTerminal = {
   test: Place;
   consequent: BlockId;
   alternate: BlockId;
-  fallthrough: BlockId | null;
+  fallthrough: BlockId;
   id: InstructionId;
   loc: SourceLocation;
 };
@@ -443,13 +457,14 @@ export type BranchTerminal = {
   alternate: BlockId;
   id: InstructionId;
   loc: SourceLocation;
+  fallthrough?: never;
 };
 
 export type SwitchTerminal = {
   kind: "switch";
   test: Place;
   cases: Array<Case>;
-  fallthrough: BlockId | null;
+  fallthrough: BlockId;
   id: InstructionId;
   loc: SourceLocation;
 };
@@ -521,7 +536,7 @@ export type TernaryTerminal = {
 export type LabelTerminal = {
   kind: "label";
   block: BlockId;
-  fallthrough: BlockId | null;
+  fallthrough: BlockId;
   id: InstructionId;
   loc: SourceLocation;
 };
@@ -555,7 +570,7 @@ export type TryTerminal = {
   handlerBinding: Place | null;
   handler: BlockId;
   // TODO: support `finally`
-  fallthrough: BlockId | null;
+  fallthrough: BlockId;
   id: InstructionId;
   loc: SourceLocation;
 };
@@ -566,6 +581,7 @@ export type MaybeThrowTerminal = {
   handler: BlockId;
   id: InstructionId;
   loc: SourceLocation;
+  fallthrough?: never;
 };
 
 export type ReactiveScopeTerminal = {

compiler/packages/babel-plugin-react-forget/src/HIR/HIRBuilder.ts

@@ -8,7 +8,6 @@
 import { Binding, NodePath } from "@babel/traverse";
 import * as t from "@babel/types";
 import { CompilerError } from "../CompilerError";
-import { assertExhaustive } from "../Utils/utils";
 import { Environment } from "./Environment";
 import { Global } from "./Globals";
 import {
@@ -32,8 +31,8 @@ import {
 import { printInstruction } from "./PrintHIR";
 import {
   eachTerminalSuccessor,
-  mapOptionalFallthroughs,
   mapTerminalSuccessors,
+  terminalFallthrough,
 } from "./visitors";
 
 /*
@@ -329,7 +328,6 @@ export default class HIRBuilder {
     ir.blocks = rpoBlocks;
 
     removeUnreachableForUpdates(ir);
-    removeUnreachableFallthroughs(ir);
     removeDeadDoWhileStatements(ir);
     removeUnnecessaryTryCatch(ir);
     markInstructionIds(ir);
@@ -629,24 +627,6 @@ export function removeUnreachableForUpdates(fn: HIR): void {
   }
 }
 
-export function removeUnreachableFallthroughs(func: HIR): void {
-  const visited: Set<BlockId> = new Set();
-  for (const [_, block] of func.blocks) {
-    visited.add(block.id);
-  }
-
-  // Cleanup any fallthrough blocks that weren't visited
-  for (const [_, block] of func.blocks) {
-    mapOptionalFallthroughs(block.terminal, (fallthrough) => {
-      if (visited.has(fallthrough)) {
-        return fallthrough;
-      } else {
-        return null;
-      }
-    });
-  }
-}
-
 export function removeDeadDoWhileStatements(func: HIR): void {
   const visited: Set<BlockId> = new Set();
   for (const [_, block] of func.blocks) {
@@ -691,14 +671,19 @@ export function reversePostorderBlocks(func: HIR): void {
  */
 function getReversePostorderedBlocks(func: HIR): HIR["blocks"] {
   const visited: Set<BlockId> = new Set();
+  const used: Set<BlockId> = new Set();
+  const usedFallthroughs: Set<BlockId> = new Set();
   const postorder: Array<BlockId> = [];
-  function visit(blockId: BlockId): void {
-    if (visited.has(blockId)) {
+  function visit(blockId: BlockId, isUsed: boolean): void {
+    const wasUsed = used.has(blockId);
+    const wasVisited = visited.has(blockId);
+    visited.add(blockId);
+    if (isUsed) {
+      used.add(blockId);
+    }
+    if (wasVisited && (wasUsed || !isUsed)) {
       return;
     }
-    visited.add(blockId);
-    const block = func.blocks.get(blockId)!;
-    const { terminal } = block;
 
     /*
      * Note that we visit successors in reverse order. This ensures that when we
@@ -710,7 +695,7 @@ function getReversePostorderedBlocks(func: HIR): HIR["blocks"] {
      *    // bb1
      *    x = 1;
      * } else {
-     *    // b2
+     *    // bb2
      *    x = 2;
      * }
      * // bb3
@@ -721,104 +706,50 @@ function getReversePostorderedBlocks(func: HIR): HIR["blocks"] {
      * program order for visual debugging. By visiting the successors in reverse order
      * (eg bb2 then bb1), we ensure that they get reversed back to the correct order.
      */
-    switch (terminal.kind) {
-      case "return":
-      case "throw": {
-        // no-op, no successors
-        break;
-      }
-      case "goto": {
-        visit(terminal.block);
-        break;
-      }
-      case "if": {
-        /*
-         * can ignore fallthrough, if its reachable it will be reached through
-         * consequent/alternate
-         */
-        const { consequent, alternate } = terminal;
-        visit(alternate);
-        visit(consequent);
-        break;
-      }
-      case "branch": {
-        const { consequent, alternate } = terminal;
-        visit(alternate);
-        visit(consequent);
-        break;
-      }
-      case "switch": {
-        /*
-         * can ignore fallthrough, if its reachable it will be reached through
-         * a case
-         */
-        const { cases } = terminal;
-        for (const case_ of [...cases].reverse()) {
-          visit(case_.block);
-        }
-        break;
-      }
-      case "optional":
-      case "ternary":
-      case "logical": {
-        visit(terminal.test);
-        break;
-      }
-      case "do-while": {
-        visit(terminal.loop);
-        break;
-      }
-      case "while": {
-        visit(terminal.test);
-        break;
-      }
-      case "for":
-      case "for-in":
-      case "for-of": {
-        visit(terminal.init);
-        break;
-      }
-      case "label": {
-        visit(terminal.block);
-        break;
-      }
-      case "sequence": {
-        visit(terminal.block);
-        break;
-      }
-      case "maybe-throw": {
-        visit(terminal.handler);
-        visit(terminal.continuation);
-        break;
-      }
-      case "try": {
-        visit(terminal.block);
-        break;
-      }
-      case "scope": {
-        visit(terminal.block);
-        break;
-      }
-      case "unreachable":
-      case "unsupported": {
-        break;
-      }
-      default: {
-        assertExhaustive(
-          terminal,
-          `Unexpected terminal kind \`${(terminal as any).kind}\``
-        );
+    const block = func.blocks.get(blockId)!;
+    const successors = [...eachTerminalSuccessor(block.terminal)].reverse();
+    const fallthrough = terminalFallthrough(block.terminal);
+
+    /**
+     * Fallthrough blocks are only used to record original program block structure. If the
+     * fallthrough is actually reachable, it will be reached through terminal successors.
+     * To retain program structure, we visit fallthrough blocks first (marking them as not
+     * actually used yet) to ensure their block IDs emitted in the correct order.
+     */
+    if (fallthrough != null) {
+      if (isUsed) {
+        usedFallthroughs.add(fallthrough);
       }
+      visit(fallthrough, false);
+    }
+    for (const successor of successors) {
+      visit(successor, isUsed);
     }
 
-    postorder.push(blockId);
+    if (!wasVisited) {
+      postorder.push(blockId);
+    }
   }
-  visit(func.entry);
-
-  const blocks = new Map();
+  visit(func.entry, true);
+  const blocks = new Map<BlockId, BasicBlock>();
   for (const blockId of postorder.reverse()) {
-    blocks.set(blockId, func.blocks.get(blockId)!);
+    const block = func.blocks.get(blockId)!;
+    if (used.has(blockId)) {
+      blocks.set(blockId, func.blocks.get(blockId)!);
+    } else if (usedFallthroughs.has(blockId)) {
+      blocks.set(blockId, {
+        ...block,
+        instructions: [],
+        terminal: {
+          kind: "unreachable",
+          id: block.terminal.id,
+          loc: block.terminal.loc,
+        },
+      });
+    }
+    // otherwise this block is unreachable
   }
+
   return blocks;
 }
 
@@ -847,6 +778,14 @@ export function markPredecessors(func: HIR): void {
   const visited: Set<BlockId> = new Set();
   function visit(blockId: BlockId, prevBlock: BasicBlock | null): void {
     const block = func.blocks.get(blockId)!;
+    if (block == null) {
+      return;
+    }
+    CompilerError.invariant(block != null, {
+      reason: "unexpected missing block",
+      description: `block ${blockId}`,
+      loc: GeneratedSource,
+    });
     if (prevBlock) {
       block.preds.add(prevBlock.id);
     }
@@ -879,7 +818,7 @@ function getTargetIfIndirection(block: BasicBlock): number | null {
 
 /*
  * Finds try terminals where the handler is unreachable, and converts the try
- * to a goto(terminal.fallthrough)
+ * to a goto(terminal.block)
  */
 export function removeUnnecessaryTryCatch(fn: HIR): void {
   for (const [, block] of fn.blocks) {
@@ -887,6 +826,9 @@ export function removeUnnecessaryTryCatch(fn: HIR): void {
       block.terminal.kind === "try" &&
       !fn.blocks.has(block.terminal.handler)
     ) {
+      const handlerId = block.terminal.handler;
+      const fallthroughId = block.terminal.fallthrough;
+      const fallthrough = fn.blocks.get(fallthroughId);
       block.terminal = {
         kind: "goto",
         block: block.terminal.block,
@@ -894,6 +836,15 @@ export function removeUnnecessaryTryCatch(fn: HIR): void {
         loc: block.terminal.loc,
         variant: GotoVariant.Break,
       };
+
+      if (fallthrough != null) {
+        if (fallthrough.preds.size === 1 && fallthrough.preds.has(handlerId)) {
+          // delete fallthrough
+          fn.blocks.delete(fallthroughId);
+        } else {
+          fallthrough.preds.delete(handlerId);
+        }
+      }
     }
   }
 }

compiler/packages/babel-plugin-react-forget/src/HIR/MergeConsecutiveBlocks.ts

@@ -13,8 +13,8 @@ import {
   HIRFunction,
   Instruction,
 } from "./HIR";
-import { markPredecessors, removeUnreachableFallthroughs } from "./HIRBuilder";
-import { mapOptionalFallthroughs, terminalFallthrough } from "./visitors";
+import { markPredecessors } from "./HIRBuilder";
+import { terminalFallthrough, terminalHasFallthrough } from "./visitors";
 
 /*
  * Merges sequences of blocks that will always execute consecutively —
@@ -113,10 +113,11 @@ export function mergeConsecutiveBlocks(fn: HIRFunction): void {
     fn.body.blocks.delete(block.id);
   }
   markPredecessors(fn.body);
-  for (const [, block] of fn.body.blocks) {
-    mapOptionalFallthroughs(block.terminal, (blockId) => merged.get(blockId));
+  for (const [, { terminal }] of fn.body.blocks) {
+    if (terminalHasFallthrough(terminal)) {
+      terminal.fallthrough = merged.get(terminal.fallthrough);
+    }
   }
-  removeUnreachableFallthroughs(fn.body);
 }
 
 class MergedBlocks {

compiler/packages/babel-plugin-react-forget/src/HIR/index.ts

@@ -23,7 +23,6 @@ export {
   markInstructionIds,
   markPredecessors,
   removeUnnecessaryTryCatch,
-  removeUnreachableFallthroughs,
   reversePostorderBlocks,
 } from "./HIRBuilder";
 export { mergeConsecutiveBlocks } from "./MergeConsecutiveBlocks";

compiler/packages/babel-plugin-react-forget/src/HIR/visitors.ts

@@ -634,8 +634,7 @@ export function mapTerminalSuccessors(
     case "if": {
       const consequent = fn(terminal.consequent);
       const alternate = fn(terminal.alternate);
-      const fallthrough =
-        terminal.fallthrough !== null ? fn(terminal.fallthrough) : null;
+      const fallthrough = fn(terminal.fallthrough);
       return {
         kind: "if",
         test: terminal.test,
@@ -666,8 +665,7 @@ export function mapTerminalSuccessors(
           block: target,
         };
       });
-      const fallthrough =
-        terminal.fallthrough !== null ? fn(terminal.fallthrough) : null;
+      const fallthrough = fn(terminal.fallthrough);
       return {
         kind: "switch",
         test: terminal.test,
@@ -794,8 +792,7 @@ export function mapTerminalSuccessors(
     }
     case "label": {
       const block = fn(terminal.block);
-      const fallthrough =
-        terminal.fallthrough !== null ? fn(terminal.fallthrough) : null;
+      const fallthrough = fn(terminal.fallthrough);
       return {
         kind: "label",
         block,
@@ -829,8 +826,7 @@ export function mapTerminalSuccessors(
     case "try": {
       const block = fn(terminal.block);
       const handler = fn(terminal.handler);
-      const fallthrough =
-        terminal.fallthrough !== null ? fn(terminal.fallthrough) : null;
+      const fallthrough = fn(terminal.fallthrough);
       return {
         kind: "try",
         block,
@@ -866,12 +862,10 @@ export function mapTerminalSuccessors(
   }
 }
 
-/*
- * Helper to get a terminal's fallthrough. The main reason to extract this as a helper
- * function is to ensure that we use an exhaustive switch to ensure that we add new terminal
- * variants as appropriate.
- */
-export function terminalFallthrough(terminal: Terminal): BlockId | null {
+export function terminalHasFallthrough<
+  T extends Terminal,
+  U extends T & { fallthrough: BlockId }
+>(terminal: T): terminal is U {
   switch (terminal.kind) {
     case "maybe-throw":
     case "branch":
@@ -880,7 +874,8 @@ export function terminalFallthrough(terminal: Terminal): BlockId | null {
     case "throw":
     case "unreachable":
     case "unsupported": {
-      return null;
+      const _: undefined = terminal.fallthrough;
+      return false;
     }
     case "try":
     case "do-while":
@@ -896,7 +891,8 @@ export function terminalFallthrough(terminal: Terminal): BlockId | null {
     case "ternary":
     case "while":
     case "scope": {
-      return terminal.fallthrough;
+      const _: BlockId = terminal.fallthrough;
+      return true;
     }
     default: {
       assertExhaustive(
@@ -907,104 +903,16 @@ export function terminalFallthrough(terminal: Terminal): BlockId | null {
   }
 }
 
-export function mapOptionalFallthroughs(
-  terminal: Terminal,
-  fn: (block: BlockId) => BlockId | null
-): void {
-  switch (terminal.kind) {
-    case "maybe-throw":
-    case "branch":
-    case "goto":
-    case "return":
-    case "throw":
-    case "unreachable":
-    case "unsupported": {
-      return;
-    }
-    /*
-     * NOTE: TypeScript has a bug where it does not correctly model properties whose values are
-     * non-null in some cases and nullable in other cases, if those cases are joined together.
-     * Thus we use one block per case here to ensure that any changes to the types will cause
-     * a compiler error.
-     */
-    case "do-while": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "for-of": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "for-in": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "for": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "logical": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "optional": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "ternary": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "while": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "scope": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "switch": {
-      if (terminal.fallthrough !== null) {
-        terminal.fallthrough = fn(terminal.fallthrough);
-      } else {
-        terminal.fallthrough = null;
-      }
-      break;
-    }
-    case "if": {
-      if (terminal.fallthrough !== null) {
-        terminal.fallthrough = fn(terminal.fallthrough);
-      } else {
-        terminal.fallthrough = null;
-      }
-      break;
-    }
-    case "label": {
-      if (terminal.fallthrough !== null) {
-        terminal.fallthrough = fn(terminal.fallthrough);
-      } else {
-        terminal.fallthrough = null;
-      }
-      break;
-    }
-    case "sequence": {
-      const _: BlockId = terminal.fallthrough;
-      break;
-    }
-    case "try": {
-      if (terminal.fallthrough !== null) {
-        terminal.fallthrough = fn(terminal.fallthrough);
-      } else {
-        terminal.fallthrough = null;
-      }
-      break;
-    }
-    default: {
-      assertExhaustive(
-        terminal,
-        `Unexpected terminal kind \`${(terminal as any).kind}\``
-      );
-    }
+/*
+ * Helper to get a terminal's fallthrough. The main reason to extract this as a helper
+ * function is to ensure that we use an exhaustive switch to ensure that we add new terminal
+ * variants as appropriate.
+ */
+export function terminalFallthrough(terminal: Terminal): BlockId | null {
+  if (terminalHasFallthrough(terminal)) {
+    return terminal.fallthrough;
+  } else {
+    return null;
   }
 }
 

compiler/packages/babel-plugin-react-forget/src/Optimization/ConstantPropagation.ts

@@ -23,7 +23,6 @@ import {
   markInstructionIds,
   markPredecessors,
   mergeConsecutiveBlocks,
-  removeUnreachableFallthroughs,
   reversePostorderBlocks,
 } from "../HIR";
 import {
@@ -72,7 +71,6 @@ function constantPropagationImpl(fn: HIRFunction, constants: Constants): void {
      * Re-run minification of the graph (incl reordering instruction ids)
      */
     reversePostorderBlocks(fn.body);
-    removeUnreachableFallthroughs(fn.body);
     removeUnreachableForUpdates(fn.body);
     removeDeadDoWhileStatements(fn.body);
     removeUnnecessaryTryCatch(fn.body);

compiler/packages/babel-plugin-react-forget/src/Optimization/PruneMaybeThrows.ts

@@ -15,7 +15,6 @@ import {
   assertConsistentIdentifiers,
   assertTerminalSuccessorsExist,
   mergeConsecutiveBlocks,
-  removeUnreachableFallthroughs,
   reversePostorderBlocks,
 } from "../HIR";
 import {
@@ -39,7 +38,6 @@ export function pruneMaybeThrows(fn: HIRFunction): void {
      * Re-run minification of the graph (incl reordering instruction ids)
      */
     reversePostorderBlocks(fn.body);
-    removeUnreachableFallthroughs(fn.body);
     removeUnreachableForUpdates(fn.body);
     removeDeadDoWhileStatements(fn.body);
     removeUnnecessaryTryCatch(fn.body);

compiler/packages/babel-plugin-react-forget/src/ReactiveScopes/BuildReactiveFunction.ts

@@ -112,7 +112,7 @@ class Driver {
       }
       case "if": {
         const fallthroughId =
-          terminal.fallthrough !== null &&
+          this.cx.reachable(terminal.fallthrough) &&
           !this.cx.isScheduled(terminal.fallthrough)
             ? terminal.fallthrough
             : null;
@@ -176,7 +176,7 @@ class Driver {
       }
       case "switch": {
         const fallthroughId =
-          terminal.fallthrough !== null &&
+          this.cx.reachable(terminal.fallthrough) &&
           !this.cx.isScheduled(terminal.fallthrough)
             ? terminal.fallthrough
             : null;
@@ -289,7 +289,7 @@ class Driver {
       }
       case "while": {
         const fallthroughId =
-          terminal.fallthrough !== null &&
+          this.cx.reachable(terminal.fallthrough) &&
           !this.cx.isScheduled(terminal.fallthrough)
             ? terminal.fallthrough
             : null;
@@ -350,11 +350,9 @@ class Driver {
             ? terminal.loop
             : null;
 
-        const fallthroughId =
-          terminal.fallthrough !== null &&
-          !this.cx.isScheduled(terminal.fallthrough)
-            ? terminal.fallthrough
-            : null;
+        const fallthroughId = !this.cx.isScheduled(terminal.fallthrough)
+          ? terminal.fallthrough
+          : null;
 
         const scheduleId = this.cx.scheduleLoop(
           terminal.fallthrough,
@@ -437,11 +435,9 @@ class Driver {
             ? terminal.loop
             : null;
 
-        const fallthroughId =
-          terminal.fallthrough !== null &&
-          !this.cx.isScheduled(terminal.fallthrough)
-            ? terminal.fallthrough
-            : null;
+        const fallthroughId = !this.cx.isScheduled(terminal.fallthrough)
+          ? terminal.fallthrough
+          : null;
 
         const scheduleId = this.cx.scheduleLoop(
           terminal.fallthrough,
@@ -512,11 +508,9 @@ class Driver {
             ? terminal.loop
             : null;
 
-        const fallthroughId =
-          terminal.fallthrough !== null &&
-          !this.cx.isScheduled(terminal.fallthrough)
-            ? terminal.fallthrough
-            : null;
+        const fallthroughId = !this.cx.isScheduled(terminal.fallthrough)
+          ? terminal.fallthrough
+          : null;
 
         const scheduleId = this.cx.scheduleLoop(
           terminal.fallthrough,
@@ -626,7 +620,7 @@ class Driver {
       }
       case "label": {
         const fallthroughId =
-          terminal.fallthrough !== null &&
+          this.cx.reachable(terminal.fallthrough) &&
           !this.cx.isScheduled(terminal.fallthrough)
             ? terminal.fallthrough
             : null;
@@ -747,7 +741,7 @@ class Driver {
       }
       case "try": {
         const fallthroughId =
-          terminal.fallthrough !== null &&
+          this.cx.reachable(terminal.fallthrough) &&
           !this.cx.isScheduled(terminal.fallthrough)
             ? terminal.fallthrough
             : null;
@@ -1241,6 +1235,11 @@ class Context {
     this.#catchHandlers.add(block);
   }
 
+  reachable(id: BlockId): boolean {
+    const block = this.ir.blocks.get(id)!;
+    return block.terminal.kind !== "unreachable";
+  }
+
   /*
    * Record that the given block will be emitted (eg by the codegen of a parent node)
    * so that child nodes can avoid re-emitting it.

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/try-catch-in-nested-scope.expect.md

@@ -40,38 +40,46 @@ import { unstable_useMemoCache as useMemoCache } from "react";
 import { mutate, setProperty, throwErrorWithMessageIf } from "shared-runtime";
 
 function useFoo(t0) {
-  const $ = useMemoCache(3);
+  const $ = useMemoCache(6);
   const { value, cond } = t0;
+  let y;
   let t1;
   if ($[0] !== value || $[1] !== cond) {
     t1 = Symbol.for("react.early_return_sentinel");
     bb0: {
-      const y = [value];
-      const x = { cond };
-      try {
-        mutate(x);
-        throwErrorWithMessageIf(x.cond, "error");
-      } catch {
-        setProperty(x, "henderson");
-        t1 = x;
-        break bb0;
+      y = [value];
+      let x;
+      if ($[4] !== cond) {
+        x = { cond };
+        try {
+          mutate(x);
+          throwErrorWithMessageIf(x.cond, "error");
+        } catch {
+          setProperty(x, "henderson");
+          t1 = x;
+          break bb0;
+        }
+
+        setProperty(x, "nevada");
+        $[4] = cond;
+        $[5] = x;
+      } else {
+        x = $[5];
       }
-
-      setProperty(x, "nevada");
       y.push(x);
-
-      t1 = y;
-      break bb0;
     }
     $[0] = value;
     $[1] = cond;
-    $[2] = t1;
+    $[2] = y;
+    $[3] = t1;
   } else {
-    t1 = $[2];
+    y = $[2];
+    t1 = $[3];
   }
   if (t1 !== Symbol.for("react.early_return_sentinel")) {
     return t1;
   }
+  return y;
 }
 
 export const FIXTURE_ENTRYPOINT = {

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/try-catch-try-value-modified-in-catch.expect.md

@@ -45,9 +45,6 @@ function Component(props) {
         t0 = e;
         break bb0;
       }
-
-      t0 = null;
-      break bb0;
     }
     $[0] = props.y;
     $[1] = props.e;
@@ -58,6 +55,7 @@ function Component(props) {
   if (t0 !== Symbol.for("react.early_return_sentinel")) {
     return t0;
   }
+  return null;
 }
 
 export const FIXTURE_ENTRYPOINT = {

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/try-catch-with-catch-param.expect.md

@@ -31,12 +31,13 @@ import { unstable_useMemoCache as useMemoCache } from "react";
 const { throwInput } = require("shared-runtime");
 
 function Component(props) {
-  const $ = useMemoCache(1);
+  const $ = useMemoCache(2);
+  let x;
   let t0;
   if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
     t0 = Symbol.for("react.early_return_sentinel");
     bb0: {
-      const x = [];
+      x = [];
       try {
         throwInput(x);
       } catch (t1) {
@@ -45,17 +46,17 @@ function Component(props) {
         t0 = e;
         break bb0;
       }
-
-      t0 = x;
-      break bb0;
     }
-    $[0] = t0;
+    $[0] = x;
+    $[1] = t0;
   } else {
-    t0 = $[0];
+    x = $[0];
+    t0 = $[1];
   }
   if (t0 !== Symbol.for("react.early_return_sentinel")) {
     return t0;
   }
+  return x;
 }
 
 export const FIXTURE_ENTRYPOINT = {