[release/8.0 staging] Port fix for 103477 to 8.0 #103918
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"Port" the changes from dotnet#103788 to .NET 8. We don't have the DFS tree, so enhance the topological sort that SSA uses to detect cycles and backedges. Use this info to stop searching for redundant zero inits once flow from entry has entered a cycle. Fixes dotnet#103477 (for .NET 8).
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
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@dotnet/jit-contrib PTAL |
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@mangod9 since Jeff is OOF perhaps you and Julie can co-approve? |
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@AndyAyersMS friendly reminder that code complete for the August Release is July 15th. If you want this fix to be included in that release, please merge this PR before that date. |
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Friendly reminder that Monday July 15th is Code Complete day, that's the deadline to get this included in the August Release. |
Thanks for the remainders! |
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"Port" the changes from #103788 to .NET 8.
We don't have the DFS tree, so enhance the topological sort that SSA uses to detect cycles and backedges.
Use this info to stop searching for redundant zero inits once flow from entry has entered a cycle.
Fixes #103477 (for .NET 8).
Customer Impact
In #103477 the customer reported silent bad code where a necessary zero initialization was removed via JIT optimization.
Regression
The issue was introduced in .NET 8
Testing
Verified repro (with jitted code) now passes; added test case. SPMI runs show we now keep a small number of other zero initializations that were previously (correctly) deemed redundant.
Risk
Low. This is making an optimization more conservative.