[llvm-branch-commits] [llvm] release/22.x: [Hexagon] Fix AP register use-before-def and add MIR serialization for liveness tracking (#191010) (PR #192036)

[Brian Cain via llvm-branch-commits]

androm3da wrote:

> > > this feels like it goes beyond critical bug fixes to be honest
> > 
> > 
> > IMO this bugfix is my highest-ranked one for 22.x Hexagon codegen, I've been anxiously awaiting its landing on `main`. Other cherry-picks could arguably be sub-critical but not this one.
> > What about this PR seems like it's beyond a critical bugfix?
> 
> it was the new MIR serialization and `BUILD_SHARED_LIBS=OFF` being missed initially that caught my eye, but I didn't look that closely

I'm not 100% positive how critical that part is here.  IIUC the original codegen change was the important bit, and I think the MIR changes were required to fix inconsistencies in the test cases?  Maybe @pkarveti can help clarify.  Pavani, if we omitted the MIRParser linkage change (and related change to ` HexagonTargetMachine::parseMachineFunctionInfo()`?), what would be the impact?  I guess the codegen change could come by itself but we would be left without a corresponding lit test case on `release/22.x`?

> > > are you confident this has had enough testing?
> > 
> > 
> > This is a fair question. After this landed, we don't see any regression on `main` with the `llvm-test-suite` configs I tested. But I haven't yet tried to build the project that revealed this codegen error (libeigen), to confirm it's effective.
> > Since I am looking forward to this change landing on 22.x, I'm willing to do any additional testing desired. Also @pkarveti let me know if you have any ideas for cases that could evoke weaknesses in this change.
> 
> Ok, it's your backend at the end of the day and any fallout should be contained at least so am happy to backport as long as you're confident. 22.1.4 is next Tuesday.

Okay, I think we can give a definitive answer about the intended scope of this PR by Monday.  But IMO plan A is take it as-is.  Thanks!

https://github.com/llvm/llvm-project/pull/192036