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JIT: have jit tail call stress avoid creating loops in some cases - #73114
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Set `lvHasILStoreOp` on `this` right when the local is created, so that subsequent logic in the JIT sees a consistent value. Fixesdotnet#73090.
AndyAyersMS
commented
Jul 30, 2022
cc @dotnet/jit-contrib |
ghost
commented
Jul 30, 2022
Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch Issue DetailsSet Fixes #73090.
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AndyAyersMS
commented
Jul 30, 2022
/azp run runtime-coreclr libraries-jitstress |
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Azure Pipelines successfully started running 1 pipeline(s). |
AndyAyersMS
commented
Jul 30, 2022
Bug was different than I thought -- jit stress was creating modifiable Fix is to disallow tail call stress from creating the loop. |
AndyAyersMS
commented
Jul 30, 2022
/azp run runtime-coreclr jitstress |
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Azure Pipelines successfully started running 1 pipeline(s). |
| // Avoid setting compHasBackwardsJump = true via tail call stress if the method cannot have | ||
| // patchpoints. | ||
| // | ||
| const bool mayHavePatchpoints = opts.jitFlags->IsSet(JitFlags::JIT_FLAG_TIER0) && | ||
| (JitConfig.TC_OnStackReplacement() > 0) && | ||
| compCanHavePatchpoints(); | ||
| if (passedConstraintCheck && (mayHavePatchpoints || compHasBackwardJump)) |
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The fix looks fine to me but I am a bit confused we are marking a backward jump in the first place. We should not do the loop optimization in tier-0 (and, since #41059, never under tailcall stress).
I can clean this up in the future if you don't want to do this as part of this PR.
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But clearly you had to add special support for OSR due to the tailcall-to-loop optimization, so maybe I am missing something?
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No, you're on to something.
We are probably too aggressive in marking explicit tail calls as backwards branches in Tier0—and more importantly in this case, changing the value of compHasBackwardJump. We do this regardless of optimization flags. If we are never going to do the optimization, then we don't need to change compHasBackwardJump either.
Another possible fix would be that when tail call stress changes an implicit tail call to an explicit one, it should also set compTailPrefixSeen. But it's not as clean of a fix; we might already have added some patchpoints.
AndyAyersMS
commented
Jul 31, 2022
I'll merge this to fix jitstress. Not sure if I'll have time today to do anything more. |
Don't create a loop via tail call stress if the method didn't already have a loop and could have patchpoints.
Fixes#73090.