[llvm] [VPlan] Generalize collectUsersInExitBlocks for multiple exit bbs. (PR #115066)

[David Sherwood via llvm-commits]

david-arm wrote:

> > This is trying to avoid having to add extra code dealing with the exit phis following on the suggestions/comments in https://github.com/llvm/llvm-project/pull/112138/files#r1810491008. #112138 still only handles live-ins in exit phis, but in the latest version it doesn't have to update the VPIRInstructions; instead it rejects any VPlans that contains VPIRInstructions without operands (i.e. because they are live-out inductions) or any of their added operands aren't live-ins. Alternatively I could also restore the code from https://github.com/llvm/llvm-project/pull/112138/files#r1810491008, WDYT?
> 
> IIRC we briefly talked about having support for phis that use only live-outs to test the whole structure more end-to-end, but another alternative would be to check the exit blocks for any VPIRInstruction instead of the current check around https://github.com/llvm/llvm-project/pull/112138/files#diff-da321d454a7246f8ae276bf1db2782bf26b5210b8133cb59e4d7fd45d0905decR9196

Hi @fhahn, thanks for the quick response! When I was looking at this patch yesterday PR #112138 hadn't been updated - I think there must have been an incorrect version pushed up because you'd addressed some comments but the code hadn't changed. So I was lacking some context about what how this patch fits in with that, but now I see your updated version and it makes more sense now! And I understand you're trying to limit the patch to only handling live-ins, which is fine. I'm currently reviewing your latest version of PR #112138 first, then I'll come back to this.

https://github.com/llvm/llvm-project/pull/115066