Re: Add missing JIT inline pass for llvm>=17

On Thu, Jan 15, 2026 at 2:51 PM Andres Freund <andres@anarazel.de> wrote:
> I'm strongly against removing the always inline pass, I see absolutely no
> reason for doing that. The whole point of always inline is that it happens
> unconditionally. It's not an expensive pass either.

I've looked into more details on what was provided by 'default<O0>',
and it turns out it includes an always-inline pass[0]. This is also
visible when using debug-pass-manager:

llvm-as < /dev/null | opt -disable-output --passes='default<O0>'
-debug-pass-manager
Running analysis: InnerAnalysisManagerProxy<FunctionAnalysisManager,
Module> on [module]
Running pass: AlwaysInlinerPass on [module]
Running analysis: ProfileSummaryAnalysis on [module]
Running pass: CoroConditionalWrapper on [module]
Running pass: VerifierPass on [module]
Running analysis: VerifierAnalysis on [module]

With the pre-LLVM17 legacy pass manager, that doesn't seem to be the
case[1] (despite the confusing comment? Inliner is only set by
LLVMPassManagerBuilderUseInlinerWithThreshold).

So, with 'default<O0>,mem2reg', we replicate the same behaviour as
pre-LLVM17 as it includes the always-inline pass.

I've updated the patch to only add the inline pass when PGJIT_INLINE
is on. I've also added a comment to mention that always-inline is
included in O0.

[0]:
https://github.com/llvm/llvm-project/blob/701040d48f759369dce755f185a21aa6b92ba3ae/llvm/lib/Passes/PassBuilderPipelines.cpp#L2360-L2365
[1]: https://github.com/llvm/llvm-project/blob/release/16.x/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp#L290-L313