[release/9.0-rc1] JIT: Remove implicit fallthrough assert in bool optimizer #106542
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
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cc @dotnet/jit-contrib, @AndyAyersMS @jeffschwMSFT PTAL. Thanks! |
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We have a very short window for merging RC1 backports. Please send the email to Tactics requesting approval and get a code review sign-off from area owners ASAP. |
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@carlossanlop is it not enough to get approval from @jeffschwMSFT for RC1 backports (edit: answered offline)? ping @AndyAyersMS |
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Aug 16, 2024
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Backport of #106492 to release/9.0-rc1
/cc @amanasifkhalid
Customer Impact
Recent refactors of the JIT's flowgraph implementation removed various invariants. The assert being removed by this fix enforces an invariant which no longer exists, and thus can fire for valid state. This failure was hit by Antigen, one of our fuzz test generators.
Regression
#97488 probably made this assert overzealous. That change removed logic maintaining the false target of a conditional basic block as its next block. This means it is now possible for a conditional block to be the last block in a method if both of its successors are behind it.
Testing
Triggering this assert required a pretty specific code pattern, such that a method would end with a loop with an exit condition that can be optimized, and flowgraph churn in earlier JIT phases would keep the conditional block at the end of the method. There isn't any new behavior to test here.
Risk
Low. The fix simply removes a debug assert to keep CI clean. Release builds were unaffected by this assert.