[PATCH] D157805: [BPF] Reset machine register kill mark in BPFMISimplifyPatchable

[Eduard Zingerman via Phabricator via llvm-commits]

eddyz87 added a comment.

In D157805#4583287 <https://reviews.llvm.org/D157805#4583287>, @yonghong-song wrote:

> LGTM. Thanks for detailed comments to show why generated code is incorrect. Do you think we should backport this fix to llvm17?

On the one hand the code dates back to Dec 2019 and I don't see it affecting code generation in practice (at-least for our selftests). On the other hand it is really easy to backport. I'd say we should backport it.

In D157805#4583292 <https://reviews.llvm.org/D157805#4583292>, @yonghong-song wrote:

> With LLVM_ENABLE_EXPENSIVE_CHECKS, even with this patch, there are still some selftest llvm crashes. I guess you are probably working on this (e.g. D157806 <https://reviews.llvm.org/D157806>).

Yes, I'm aware of two more issues, the one addressed by D157806 <https://reviews.llvm.org/D157806> and the one in "BPF MachineSSA Peephole Optimization For TRUNC Eliminate":

  *** Bad machine code: Illegal virtual register for instruction ***
  - function:    _dissect
  - basic block: %bb.9 if.end10 (0x621000e80d98)
  - instruction: %24:gpr32 = MOV_rr %8:gpr32, debug-location !339; progs/bpf_flow.c:120:2 @[ progs/bpf_flow.c:161:9 ]
  - operand 0:   %24:gpr32
  Expected a GPR register, but got a GPR32 register

Which I suppose is caused by `MOV_rr` instruction generated in the end of `BPFMIPeepholeTruncElim::eliminateTruncSeq()`. I'll submit a fix for this issue a bit later.


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