[CodeGen] Fix PreISelLowering not reporting changes

[aengelke]

expandVectorPredication may change code, even if the intrinsic itself remains in the code. Report changes whenever such an intrinsic is encountered, because code could have been changed.

Another follow-up fix for #101652 to fix expensive-checks-only failure.

[rofirrim]

Right, IIRC we may only change the mask/evl but leave the intrinsic in place.

LGTM. Thanks.

[rofirrim]

Thanks @aengelke

I'll take a look at CachingVPExpander::expandVectorPredication and see whether we can make it more reasonable so we don't assume we're changing things when the intrinsic is fully legal.

Currently it reads

// Return true if and only if the intrinsic was actually removed.

but I'm not sure why it should be like that. Maybe @simoll can shed some light on this.

[aengelke]

I changed that. To include expandVectorPredication in PreISelIntrinsicLowering, I needed a way to determine whether the intrinsic was removed (i.e., whether to skip one entry in the use list of the intrinsic if it was not removed). What I think we would actually need are two return values: one indicating whether the intrinsic was removed and one indicating whether the code was changed at all.

[rofirrim]

I changed that.

Ah ok. Sorry, I missed that.

What I think we would actually need are two return values: one indicating whether the intrinsic was removed and one indicating whether the code was changed at all.

I could not find any other user of CachingVPExpander::expandVectorPredication other than PreISelLowering. Looks like we do not have to tell apart the two cases and simply knowing something has changed would be enough.