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[release/3.1] Port fix for JIT silent bad code #27972
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Release/3.1 port of dotnet/runtime#797. Fixes dotnet/runtime#764 The jit might incorrectly order a read from a struct field with an operation that modifies the field, so that the read returns the wrong value. Silent bad code; program behaves incorrectly. Yes, introduced in the 3.0 cycle. Verified the user's test case now passes; no diffs seen in any existing framework or test code. **Low**: the jit is now spilling the eval stack entries to temps in cases where it did not before; this should be conservatively safe. cc: @Brucefo ____ If we're appending an assignment whose LHS is is a location within a local struct, we need to spill all references to that struct from the eval stack. Update the existing logic for this to handle the case where the LHS is a field of a local struct, and the field is updated by unusual means (here, `initobj`). Fixes dotnet/runtime#764.
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Ah, wrong cc... cc @BruceForstall |
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Arm32 failure seems unrelated: |
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The arm32 failure was seen in the past: https://github.com/dotnet/coreclr/issues/21504 |
jeffschwMSFT
added
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jamshedd
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Servicing-approved
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Approved for Feb. |
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Moved to Mar as per Tactics. Will need to be explicitly approved for Feb, if required. |
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Approved for Feb |
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Release/3.1 port of dotnet/runtime#797.
Fixes dotnet/runtime#764
The jit might incorrectly order a read from a struct field with an operation
that modifies the field, so that the read returns the wrong value.
Customer Impact
Silent bad code; program behaves incorrectly.
Regression?
Yes, introduced during the development 3.0 cycle. 2.x behaves correctly.
Testing
Verified the user's test case now passes; no diffs seen in any existing framework
or test code.
Risk
Low: the jit is now spilling the eval stack entries to temps in cases where it
did not before; this should be conservatively safe.
cc @BruceForstall
If we're appending an assignment whose LHS is is a location within a local
struct, we need to spill all references to that struct from the eval stack.
Update the existing logic for this to handle the case where the LHS is a field
of a local struct, and the field is updated by unusual means (here,
initobj).Fixes dotnet/runtime#764.