Use LLVM 15 by default, add experimental LLVM 16 support

[gmarkall]

Changes required to use LLVM 15 by default, and to support LLVM 16 experimentally, include:

CI config:

• Bump all LLVM 14 configurations to use LLVM 15.
• Bump the LLVM 15 configurations to use LLVM 16.

Docs:

• Set RTD to use LLVM 15. Unfortunately LLVM 14 is the default on Ubuntu 22.04, and there's no way to inject an environment variable to set LLVM_CONFIG from the config file (see https://github.com/readthedocs/readthedocs.org/issues/6311). Executing update-alternatives to set llvm-config-15 as the default llvm-config also fails with a permission error. So I resorted to editing the FFI build to explicitly use llvm-config-15 in a post-checkout step.

llvmlite itself:

• Always set opaque pointers to false (they are the default in both 15 and 16, unlike 14).

• Don't initialize of ObjCARCOpts in LLVM 16 and above. This was removed in LLVM 16 by:

  commit 4153f989bab0f2f300fa8d3001ebeef7b6d9672c
  Author: Arthur Eubanks <aeubanks@google.com>
  Date:   Sun Oct 2 13:20:21 2022 -0700
  
    [ObjCARC] Remove legacy PM versions of optimization passes

• Remove the AggressiveInstCombine and PruneEH passes. These were removed from the legacy pass manager in LLVM 16 by:

  commit 70dc3b811e4926fa2c88bd3b53b29c46fcba1a90
  Author: Arthur Eubanks <aeubanks@google.com>
  Date:   Mon Oct 31 14:50:38 2022 -0700
  
    [AggressiveInstCombine] Remove legacy PM pass

  and

  commit 46fc75ab28b78a730ea21fd7daba6443937bfaac
  Author: Sebastian Peryt <sebastian.peryt@intel.com>
  Date:   Mon Sep 26 18:31:32 2022 -0700
  
    [NFC][2/n] Remove PrunePH pass

• Modify reserveAllocationSpace in the memory manager to use Align for the type of alignments in LLVM 16 - this mirrors an upstream change.
• Remove LLVM 14-specific code paths (and one vestigial LLVM < 9 path).
• Update the function attributes test to recognize the new form of memory attributes, - memory(<action>) as opposed to individual attributes like readonly. See: https://releases.llvm.org/16.0.0/docs/LangRef.html#function-attributes

[sklam]

Just noticed that this doesn't bump the llvmdev version in the conda recipe

[sklam]

It should replace the conda-recipes/llvmlite with conda-recipes/llvmlite_llvm15

[gmarkall]

Ah I thought we might just delete the LLVM 14 version separately as I didn't know if it would be a problem for the build farm setup if the recipe names changed.

[sklam]

Before this can be merged, we also need to synchronize Numba to use opaque type

[gmarkall]

@sklam many thanks for the review and pointers!

Just noticed that this doesn't bump the llvmdev version in the conda recipe

I don't think we want to do this. This PR doesn't have anything to do with llvmdev builds - the llvmdev build was merged in #1036.

It should replace the conda-recipes/llvmlite with conda-recipes/llvmlite_llvm15

This is now done (and I've also done the same with the llvmdev recipe, since the llvmdev 14 recipe is no longer needed).

Before this can be merged, we also need to synchronize Numba to use opaque type

I don't think we want to do this. I thought that the plan was:

1. Bump to LLVM 15
2. Switch Numba to Opaque Pointers
3. Bump to LLVM 16+ (once other pre-requisites are solved)

This is because as I understand it, the typed / opaque pointer support in LLVM versions is:

• 14: Typed default and supported, Opaque experimental
• 15: Typed supported, Opaque default supported
• 16: Typed "best-effort" / deprecated, Opaque default supported
• 17: Typed unsupported, Opaque supported

We still unconditionally disable opaque pointers in llvmlite with this PR, so Numba should be unaffected for now, and we are in a position to be able to switch to Opaque Pointers smoothly on an LLVM version (15) that supports both, without having to worry about experimental-related issues (Opaque Pointers on 14) or bitrot (Typed Pointers on 16).

[gmarkall]

Just to add a little to my last comment - I don't think we should be testing Numba with LLVM 16 yet, the CI for LLVM 16 here is only for llvmlite development to ensure future compatibility, with no expectation that Numba works with that configuration yet.

[gmarkall]

xref: llvmlite Opaque Pointer support is in #1064.

[sklam]

CI is good. I've build this PR on the buildfarm llvmlite dag and tested the artifacts manually against numba main.

[doko42]

there's no way to inject an environment variable to set LLVM_CONFIG from the config file

update PATH before starting your build:

PATH=/usr/lib/llvm-/bin:$PATH llvm-config

[gmarkall]

there's no way to inject an environment variable to set LLVM_CONFIG from the config file

update PATH before starting your build:

PATH=/usr/lib/llvm-/bin:$PATH llvm-config

How do you do that in the context of our RTD configuration?

[doko42]

sorry, I don't know about RTD configuration

[gmarkall]

sorry, I don't know about RTD configuration

For some background, the problem with RTD configuration is that you can't set environment variables in it as far as I know (from the linked issue in the description of this PR). If I could set an environment variable before starting the build, I'd be able to set LLVM_CONFIG to point to the correct llvm-config binary, and there wouldn't be any need for workarounds like running sed over the build script.