dialects: (llvm) MLIR LLVM dialect NullOp replaced by ZeroOp

[mcjamieson]

The MLIR NullOp has been replaced by ZeroOp (see: llvm/llvm-project#67183).

This has been highlighted by the HLFIR changes and related upgrade to 'flang-new' v18.

[mcjamieson]

We will need to not only update the LLVM dialect but also lower_mpi.py transform.

[PapyChacal]

I'm curious, can I see a specific error or problem you faced? AFAIU we test this transformation in the DeVito fork's CI and nothing appeared wrong there.
Pinging @AntonLydike and @georgebisbas in case they know something I don't on that point?

[mcjamieson]

loc("generated/module_1.mlir":3:10): error: LLVM Translation failed for operation: llvm.mlir.null
error: failed to create the LLVM module
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: flang-new -fc1 -emit-obj generated/module_1.mlir

builtin.module {
  func.func @_QQmain() {
    %0 = "llvm.mlir.null"() : () -> !llvm.ptr
    %1 = func.call @MPI_Init(%0, %0) : (!llvm.ptr, !llvm.ptr) -> i32
...

With ZeroOp (llvm.mlir.zero), all is good:

builtin.module {
  func.func @_QQmain() {
    %0 = "llvm.mlir.zero"() : () -> !llvm.ptr
    %1 = func.call @MPI_Init(%0, %0) : (!llvm.ptr, !llvm.ptr) -> i32
...

[PapyChacal]

Right, MPI_Init is the only used of this op and we don't use from xDSL in DeVito...
Nevermind @georgebisbas and @AntonLydike 🙂