[WIP] LLVM rebasing efforts

[ivanradanov]

(This is on top of #355)

WIP PR for rebasing to latest llvm-project.

As llvm deprecated typed pointers we would need to eventually remove all usage of them in Polygeist as well if my understanding is correct.

Another big part that is affected by the removal of typed llvm pointers is the AST->MLIR frontend (cgeist).
The LLVM dialect code-gen there is mostly unused as it was for ABI compatibility issues we have mostly solved.

So I would say we should remove all usage of the LLVM dialect (except the struct and array types) in the frontend while doing the rebase to make our lives easier. This might require some new additions to the polygeist dialect.

• Fix backend LLVM dialect codegen
• (Optional) Add Polygeist struct/class type to use instead of LLVM::Struct
  • Remove LLVM dialect codegen in frontend
  • Variadic functions without LLVMFuncOp?
• I did not manage to figure out how to add dependencies of passes on dialect extension (specifically parallel-lower depends on the inliner interface extension of func), fix?
• polygeist-opt tests
• cgeist tests

[ivanradanov]

@wsmoses

Can you take a look at what we should be doing here instead?

[ivanradanov]

Most of the remaining failing tests are related to this

[wsmoses]

in LLVM itself there is a getFunctionType from the CallInst.

we should use the MLIR-equivalent of that here to get FT

[wsmoses]

LLVM: https://llvm.org/doxygen/InstrTypes_8h_source.html#l01270

MLIR: https://github.com/llvm/llvm-project/blob/b300f8c89829f920102e6ec5acc7d1b134bcff75/mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td#L628

I don't immediately see anything upstream MLIR that does the LLVM similar. @ftynse if you know offhand

If not we may need to add support to upstream MLIR for

[ftynse]

I think the assumption so far was that functions are non-variadic so the function type can be trivially reconstructed from the lists of operands and results of the call op. For variadic functions, there's a FIXME just above: https://github.com/llvm/llvm-project/blob/b300f8c89829f920102e6ec5acc7d1b134bcff75/mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td#L584-L586

[ivanradanov]

@wsmoses I think this is now ready?
I have XFAIL'ed two of the polygeist-opt tests because they need more substantial changes - namely fixing LLVM Opaque Pointer mem2reg and fixing a bug in the AffineBufferElimination optimization (currently disabled)

This also contains the changes in #355, (If they look good) I will squash in two different commits I think, one for the previous pr, and one for this.