GH-113464: A copy-and-patch JIT compiler by brandtbucher · Pull Request #113465...

edited by bedevere-app bot

'Twas the night before Christmas, when all through the code
Not a core dev was merging, not even Guido;
The CI was spun on the PRs with care
In hopes that green check-markings soon would be there;
The buildbots were nestled all snug under desks,
Even PPC64 AIX;
Doc-writers, triage team, the Council of Steering,
Had just stashed every change and stopped engineering,

When in the "PRs" tab arose such a clatter,
They opened GitHub to see what was the matter.
Away to CPython they flew like a flash,
Towards sounds of PROT_EXEC and __builtin___clear_cache.
First LLVM was downloaded, unzipped
Then the Actions were running a strange new build script,
When something appeared, they were stopped in their tracks,
jit_stencils.h, generated from hacks,
With their spines all a-shiver, they muttered "Oh, shit...",
They knew in a moment it must be a JIT.

More rapid than interpretation it came
And it copied-and-patched every stencil by name:
"Now, _LOAD_FAST! Now, _STORE_FAST! _BINARY_OP_ADD_INT!
On, _GUARD_DORV_VALUES_INST_ATTR_FROM_DICT!
To the top of the loop! And down into the call!
Now cache away! Cache away! Cache away all!"
But why now? And how so? They needed a hint,
Thankfully, Brandt gave a great talk at the sprint;
So over to YouTube the reviewers flew,
They read the white paper, and the blog post too.

And then, after watching, they saw its appeal
Not writing the code themselves seemed so unreal.
And the platform support was almost too easy,
ARM64 Macs to 32-bit PCs.
There was some runtime C, not too much, just enough,
Basically a loader, relocating stuff;
It ran every test, one by one passed them all,
With not one runtime dependency to install.
Mostly build-time Python! With strict static typing!
For maintenance ease, and also nerd-sniping!

Though dispatch was faster, the JIT wasn't wise,
And the traces it used still should be optimized;
The code it was JIT'ing still needed some thinning,
With code models small, and some register pinning;
Or new calling conventions, shared stubs for paths slow,
Since this JIT was brand new, there was fruit hanging low.
It was awkwardly large, parsed straight out of the ELFs,
And they laughed when they saw it, in spite of themselves;

A configure flag, and no merging this year,
Soon gave them to know they had nothing to fear;
It wasn't much faster, at least it could work,
They knew that'd come later; no one was a jerk,
But they were still smart, and determined, and skilled,
They opened a shell, and configured the build;
--enable-experimental-jit, then made it,
And away the JIT flew as their "+1"s okay'ed it.
But they heard it exclaim, as it traced out of sight,
"Happy JIT-mas to all, and to all a good night!"

• Issue: JIT Compilation #113464

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