[6.4.1] LoopInvariantCodeMotion: don't hoist and sink store [assign] - #92506
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This was accidentally enabled by 4114b28, which moved the collection of `loadsAndStores` from `collectMovableInstructions` (where stores with an `assign` ownership were filtered out) to the new `collectSpeculativelyMovableInstructions`, which doesn't filter at all. `hoistAndSinkLoadAndStore` doesn't support `store [assign]`: it erases the store without destroying the overwritten value, which leaks the value coming from the SSAUpdater's phi argument Reject such access paths in `isOnlyLoadedAndStored` again and remove the now dead ownership check in `collectMovableInstructions`. Fixes an ownership verifier error rdar://183953843 (cherry picked from commit 3f5c32d)
eeckstein
changed the title
store [assign]store [assign]
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tbkka
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Sep 22, 2026
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Explanation:
We're hitting an error (
SIL memory lifetime failure in <symbol>: memory is not initialized, but should be) when building some of our internal projects in release mode against a 6.4.x snapshot toolchain. I couldn't reproduce with recent main snapshots. I initially thought it was because that mem2reg pass was removed on main, but I was able to narrow this down to being resolved by LoopInvariantCodeMotion: don't hoist and sinkstore [assign]#91219.We do have a short-term workaround to remove the inlining on the code that triggers this, but it causes a pretty severe performance regression that we can't afford to incur in the longer term.
Scope:
Limited to
LoopInvariantCodeMotion. The change breaks out of a previously attempted optimization when there's astore [assign]in the loop.Issues:
rdar://183953843
6.4.0 miscompile: dead-store elimination incorrectly deletes the defer writeback #92486
Original PRs:
main: LoopInvariantCodeMotion: don't hoist and sink
store [assign]#912196.4.x: [🍒 6.4] LoopInvariantCodeMotion: don't hoist and sink
store [assign]#91509Risk:
Low. It's a trivial change which makes load-store optimization in LICM more conservative. This drops an optimization opportunity that lead to a crash and failure to compile in release mode.
Testing:
Adds
dont_hoist_store_assigntest case totest/SILOptimizer/licm.sil. Locally, I've also built a toolchain from a recent 6.4.x snapshot plus this commit and confirmed that a package which reproduces the failure builds successfully.Reviewers:
@aidan-hall