Mark all GC functions as yk_outline.#131
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vext01 merged 1 commit intoykjit:mainfrom Aug 24, 2025
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There are few, if any, GC functions that we want to trace directly but at the moment, SWT inserts tracing blocks which (a) slows these functions down in all cases (b) particularly slows them down if tracing is active. At first I started going through these individually, seeing which end up being outlined before realising that really what I want to do is say "all of the functions in this file should be outlined". I don't believe there's a way to attach such an attribute to a file in LLVM -- or, at least, we don't have the right hooks for it in ykllvm right now -- so this commit simply marks every function in this file as `yk_outline`. It wouldn't surprise me if, in the future, we come back and unmark one or two functions, but I doubt we'll need or want to do that soon. Across our benchmark suite this leads to a sizeable performance increase, with many benchmarks improving by around 8-9%.
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In ykjit#131 I added `yk_outline` to nearly every GC function and got an 8-9% speedup. Much has changed since then in how we optimise programs, so I decided to revisit this. First, as I noted in ykjit#131, I was sloppy and added `yk_outline` to functions with loops in (i.e. those that could never be inlined). Those are easily removed. Indeed, _most_ of the static functions in this file can't be reached (even indirectly) from the outside world, so most of those can also have `yk_outline` removed. Really what we have to think about are the `luaC_*` functions. A quick bit of experimentation suggests that, at least for now, they're best left outlined. Overall, this commit has no meaningful performance change that I can measure.
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There are few, if any, GC functions that we want to trace directly but at the moment, SWT inserts tracing blocks which (a) slows these functions down in all cases (b) particularly slows them down if tracing is active.
At first I started going through these individually, seeing which end up being outlined before realising that really what I want to do is say "all of the functions in this file should be outlined". I don't believe there's a way to attach such an attribute to a file in LLVM -- or, at least, we don't have the right hooks for it in ykllvm right now -- so this commit simply marks every function in this file as
yk_outline. It wouldn't surprise me if, in the future, we come back and unmark one or two functions, but I doubt we'll need or want to do that soon.Across our benchmark suite this leads to a sizeable performance increase, with many benchmarks improving by around 8-9%.