JIT: Compute async liveness for address exposed locals#124001
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jakobbotsch merged 21 commits intodotnet:mainfrom Feb 9, 2026
Merged
JIT: Compute async liveness for address exposed locals#124001jakobbotsch merged 21 commits intodotnet:mainfrom
jakobbotsch merged 21 commits intodotnet:mainfrom
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…inopts-async-live-set
This should still give correct liveness at async suspension points given that local addresses cannot be taken across those.
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
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Pull request overview
This PR enables precise liveness computation for address-exposed locals during async transformations. Building on #123500 (which introduced full liveness computation for MinOpts with async), this change recognizes that local addresses cannot be taken across async suspension points, allowing the JIT to track address-exposed locals directly instead of conservatively treating them as always live.
Changes:
- Refactored the
Livenessclass template to support multiple liveness computation modes via compile-time template parameters (TrackAddressExposedLocals,IsEarly,EliminateDeadCode) - Replaced
fgLocalVarLiveness()with specialized functions:fgSsaLiveness(),fgAsyncLiveness(), andfgPostLowerLiveness() - Extracted
lvaComputePreciseRefCounts()fromlvaComputeRefCounts()to allow reuse in async transformations
Reviewed changes
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Show a summary per file
| File | Description |
|---|---|
| src/coreclr/jit/liveness.cpp | Major refactoring of liveness computation to use template-based specialization; added fgSsaLiveness(), fgAsyncLiveness(), fgPostLowerLiveness(); renamed member variables for clarity; inlined LiveVarAnalysis into DoLiveVarAnalysis() |
| src/coreclr/jit/async.cpp | Updated to use fgAsyncLiveness() and lvaComputePreciseRefCounts(); simplified AsyncLiveness class by removing m_hasLiveness field; added cleanup logic for unoptimized codegen |
| src/coreclr/jit/compiler.h | Added declarations for new liveness functions and lvaComputePreciseRefCounts(); removed obsolete fgLocalVarLivenessChanged and fgIsDoingEarlyLiveness fields |
| src/coreclr/jit/lclvars.cpp | Extracted lvaComputePreciseRefCounts() as a separate function for reuse |
| src/coreclr/jit/ssabuilder.cpp | Updated call from fgLocalVarLiveness() to fgSsaLiveness() |
| src/coreclr/jit/lower.cpp | Updated calls from fgLocalVarLiveness() to fgPostLowerLiveness() |
| src/coreclr/jit/compiler.cpp | Updated call from fgLocalVarLiveness() to fgSsaLiveness() |
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cc @dotnet/jit-contrib PTAL @AndyAyersMS This starts tracking address exposed locals for the liveness we do in the runtime async pass. It is based on a few observations:
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AndyAyersMS
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Feb 6, 2026
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This should still give correct liveness at async suspension points given that local addresses cannot be taken across those.
Based on #123500