[compiler] Fix for consecutive DCE'd branches with phis #33725
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This is an optimized version of @asmjmp0's fix in #31940. When we merge consecutive blocks we need to take care to rewrite later phis whose operands will now be different blocks due to merging. Rather than iterate all the blocks on each merge as in #31940, we can do a single iteration over all the phis at the end to fix them up. Note: this is a redo of #31959
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We currently inline IIFEs by creating a temporary and a labeled block w the original code. The original return statements turn into an assignment to the temporary and break out of the label. However, many cases of IIFEs are due to inlining of manual `useMemo()`, and these cases often have only a single return statement. Here, the output is cleaner if we avoid the temporary and label - so that's what we do in this PR. Note that the most complex part of the change is actually around ValidatePreserveExistingMemo - we have some logic to track the IIFE temporary reassignmetns which needs to be updated to handle the simpler version of inlining. --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/33726). * __->__ #33726 * #33725
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We currently inline IIFEs by creating a temporary and a labeled block w the original code. The original return statements turn into an assignment to the temporary and break out of the label. However, many cases of IIFEs are due to inlining of manual `useMemo()`, and these cases often have only a single return statement. Here, the output is cleaner if we avoid the temporary and label - so that's what we do in this PR. Note that the most complex part of the change is actually around ValidatePreserveExistingMemo - we have some logic to track the IIFE temporary reassignmetns which needs to be updated to handle the simpler version of inlining. --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/33726). * __->__ #33726 * #33725 DiffTrain build for [956d770](956d770)
github-actions bot
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Jul 8, 2025
We currently inline IIFEs by creating a temporary and a labeled block w the original code. The original return statements turn into an assignment to the temporary and break out of the label. However, many cases of IIFEs are due to inlining of manual `useMemo()`, and these cases often have only a single return statement. Here, the output is cleaner if we avoid the temporary and label - so that's what we do in this PR. Note that the most complex part of the change is actually around ValidatePreserveExistingMemo - we have some logic to track the IIFE temporary reassignmetns which needs to be updated to handle the simpler version of inlining. --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/33726). * __->__ #33726 * #33725 DiffTrain build for [956d770](956d770)
This was referenced Jul 9, 2025
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This is an optimized version of @asmjmp0's fix in #31940. When we merge consecutive blocks we need to take care to rewrite later phis whose operands will now be different blocks due to merging. Rather than iterate all the blocks on each merge as in #31940, we can do a single iteration over all the phis at the end to fix them up.
Note: this is a redo of #31959
Stack created with Sapling. Best reviewed with ReviewStack.