Assertion `getMinSignedBits() <= 64 && "Too many bits for int64_t"' failed in Loop Strength Reduction with new SCEV-based salvaging

[JosephTremoulet]

Bugzilla Link	51329
Resolution	FIXED
Resolved on	Oct 11, 2021 20:29
Version	trunk
OS	Linux
Blocks	#51489
Attachments	Small function that triggers the assertion failure in LSR
CC	@tstellar
Fixed by commit(s)	21ee38e 8988ce3

Extended Description

This assertion has been failing in some of our downstream tests each time D105207 gets checked in. I've verified that it fails at 0ba8595 but not at its parent. It also currently repros on godbolt with "assertions trunk": https://godbolt.org/z/n6T3zrsvY

Reproducer testcase attached.

[JosephTremoulet]

assigned to @chrisjbris

[JosephTremoulet]

I've verified that this still fails after 2537120 as well.

[JosephTremoulet]

I forgot to mention the command line I'm using to reproduce the issue with the attached file. It's just llc repro.ll.

[chrisjbris]

Thanks for the comprehensive report. It looks pretty obvious what the culprit is. I will add a test to make sure APInt->getSextValue() isn't called for integers greater than INTMAX and hopefully that will do the trick for now.

[chrisjbris]

Fixed with 21ee38e

[JosephTremoulet]

Fix verified, thanks.

[tstellar]

This does not cherry-pick cleanly, can someone backport it and either attach a patch or push a branch to a personal git repo on github.

[chrisjbris]

I attempted to cherry-pick the series to the release branch myself and each was clean. Three commits were necessary, which I described here: https://reviews.llvm.org/D105207. I think its not clear from this bug alone which commits are required. pehaps that was the reason for the un-clean cherry-pick attempt.

The three cherry-picks together built & passed the lit suite cleanly so I have pushed to the release branch, with original commit hashes added to the messages.

[tstellar]

Merged: 8988ce3

[tstellar]

mentioned in issue #51489