[llvm-branch-commits] [llvm] release/19.x: [llvm][CodeGen] Resolve issues when updating live intervals in window scheduler (#101945) (PR #107338)

[Hua Tian via llvm-branch-commits]

huaatian wrote:

> Hi, since we are wrapping up LLVM 19.1.0 we are very strict with the fixes we pick at this point. Can you please respond to the following questions to help me understand if this has to be included in the final release or not.
> 
> Is this PR a fix for a regression or a critical issue?
> 
> What is the risk of accepting this into the release branch?
> 
> What is the risk of NOT accepting this into the release branch?

Okay~
> Is this PR a fix for a regression or a critical issue?
1.This PR fixes an assertion failure issue introduced by our recently proposed window scheduling algorithm. This issue was reported by nathanchance when building the Linux kernel for ARCH=hexagon (reported in https://github.com/llvm/llvm-project/pull/99454).

> What is the risk of accepting this into the release branch?
2.This PR inserts three newly generated MBBs into LiveIntervals. I think the risk of this modification is low.

> What is the risk of NOT accepting this into the release branch?
3.Without this PR, there is a low probability of an assertion failure occurring in this scenario: In a function containing more than two loops, a value generated by a previous loop is used by the subsequent loop in the epilogue, and the subsequent loop successfully performs software pipelining. The issue may occur depending on the actual live interval of the value.

https://github.com/llvm/llvm-project/pull/107338