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Do not fast tail call if caller has multislot structs (#25885) #25910
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* Do not fast tail call if caller has multislot structs * apply patch * Address offline feedback
sergiy-k
approved these changes
Jul 28, 2019
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@jashook, please feel to merge this change if you and @AndyAyersMS are happy with the fix. Silent bad codegen is bad. :) |
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Will merge before the branch closes. I assume, @AndyAyersMS wont comment as it is Sunday. However, we have discussed the change that went into master (#25885). This change will force slightly less fast tail call decisions at the expense of generating correct fast tail calls.. I am happy with the change and will merge soon. Thank you for looking over the weekend @sergiy-k |
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Thanks! |
AndyAyersMS
approved these changes
Jul 28, 2019
|
Thank you @AndyAyersMS for the review! |
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Description
Silent bad codegen when compiling a method with a multislot struct argument in the caller, who has a fast tail call which re-uses the caller's stack outgoing arg space.
Customer impact
There are no currently known customers. There have been related issues in the past, but not issues filed with >16 byte structs. That being said, there is a precedent of finding these sort of problems in release once released :(. See #24858 for a very similar issue.
Regression
This is not a regression. It goes back to coreclr 1.0.
Risk
Any method in Tier 1 which is a fast tail call candidate, which also has a >16 byte struct on unix is a possible candidate for incorrect codegen. The result would be random, incorrect values passed to the callee.
Original issue:
https://github.com/dotnet/coreclr/issues/25884
/cc @dotnet/jit-contrib
/cc @sergiy-k