wrong code with -loop-reroll

[llvmbot]

Bugzilla Link	34029
Version	trunk
OS	All
Attachments	bitcode
Reporter	LLVM Bugzilla Contributor
CC	@coffezhou,@efriedma-quic,@filcab,@zmodem,@hfinkel

Extended Description

$ ./opt ~/pat.bc | ./lli
checksum = 74640FC
$ ./opt -loop-reroll ~/pat.bc | ./lli
checksum = A3DD5B7F

I'll try to reduce this once I get a chance, but putting it here so it doesn't get lost.
Also, cc:in Hal and Eli who both did some work in this area recent('ish)ly.

[llvmbot]

assigned to @efriedma-quic

[efriedma-quic]

Looks like something is going wrong optimizing main(): we find a couple of roots, but those roots don't cover the whole loop. Normally, we'd pick that up in LoopReroll::DAGRootTracker::validate, but LoopReroll::DAGRootTracker::collectUsedInstructions is marking a bunch of stuff IL_All because it depends on the induction variable.

I'm still in the process of looking at the code and trying to remember how this is supposed to work.

[zmodem]

Is this a recent regression we should track for 5.0?

[efriedma-quic]

Not a recent regression, I think... and as far as I know, reroll isn't part of the default pass pipeline.

[efriedma-quic]

*** Bug llvm/llvm-bugzilla-archive#42043 has been marked as a duplicate of this bug. ***

[efriedma-quic]

mentioned in issue llvm/llvm-bugzilla-archive#42043

[nikic]

The LoopReroll pass has been removed by #80972.