[all-commits] [llvm/llvm-project] 4159fd: [OMPIRBuilder] Avoid crash in BasicBlock::splice. ...

[Abid Qadeer via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4159fd819a89cb18e03a91576372ae257ee5fbc7
      https://github.com/llvm/llvm-project/commit/4159fd819a89cb18e03a91576372ae257ee5fbc7
  Author: Abid Qadeer <haqadeer at amd.com>
  Date:   2025-08-29 (Fri, 29 Aug 2025)

  Changed paths:
    M llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
    M llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp

  Log Message:
  -----------
  [OMPIRBuilder] Avoid crash in BasicBlock::splice. (#154987)

Calling `BasicBlock::splice` in `spliceBB` when both `Old` and `New` are
empty is a `nop` currently but it can cause a crash once debug records
are used instead of debug intrinsics. This PR makes the call conditional
on at least one of `Old` or `New` being non-empty.

Consider the following mlir:
```
omp.target map_entries() {
  llvm.intr.dbg.declare ...
  llvm.intr.dbg.declare ...
  omp.teams ...
  ...
}
```

Current code would translate llvm.intr Ops to llvm intrinsics. Old is
the BasicBlock where they were get inserted and it will have 2 llvm
debug intrinsics by the time the implementation of `omp.teams` starts.
This implementation creates many BasicBlocks by calling `splitBB`. The
`New` is the just created BasicBlock which is empty.

In the new scheme (using debug records), there will be no instruction in
the `Old` BB after llvm.intr Ops get translated but just 2 trailing
debug records. So both `Old` and `New` are empty. When control reaches
`BasicBlock::splice`, it calls `spliceDebugInfoEmptyBlock`. This
function expects that in this case (`Src` is empty but has trailing
debug records), the `ToIt` is valid and it can call `adoptDbgRecords` on
it. This assumption is not true in this case as `New` is empty and
`ToIt` is pointing to end(). The fix is to only call
`BasicBlock::splice` when at least of `Old` or `New` is not empty.



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