Horton

Re: LLVM 16 (opaque pointers)

Dmitry Dolgov <9erthalion6@gmail.com>

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From: Dmitry Dolgov <9erthalion6@gmail.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-06-04T09:33:42Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. jit: Adjust back-patch of f90b4a84 to 12 and 13.

  2. Log LLVM library version in configure output.

  3. jit: Changes for LLVM 17.

  4. jit: Supply LLVMGlobalGetValueType() for LLVM < 8.

  5. jit: Support opaque pointers in LLVM 16.

  6. jit: Reference function pointer types via llvmjit_types.c.

Attachments

> On Mon, May 22, 2023 at 03:38:44PM +1200, Thomas Munro wrote:
> Further changes are already needed for their "main" branch (LLVM
> 17-to-be), so this won't quite be enough to shut seawasp up.  At a
> glance, we will need to change from the "old pass manager" API that
> has recently been vaporised[1]
> (llvm-c/Transforms/PassManagerBuilder.h) to the new one[2][3]
> (llvm-c/Transforms/PassBuilder.h), which I suspect/hope will be as
> simple as changing llvmjit.c to call LLVMRunPasses() with a string
> describing the passes we want in "opt -passes" format, instead of our
> code that calls LLVMAddFunctionInlingPass() etc.  But that'll be a
> topic for another day, and another thread.
>
> [1] https://github.com/llvm/llvm-project/commit/0aac9a2875bad4f065367e4a6553fad78605f895
> [2] https://llvm.org/docs/NewPassManager.html
> [3] https://reviews.llvm.org/D102136

Thanks for tackling the topic! I've tested it with a couple of versions,
LLVM 12 that comes with my Gentoo box, LLVM 15 build from sources and
the modified version of patch adopted for LLVM 17 (build form sources as
well). In all three cases everything seems to be working fine.

Simple benchmarking with a query stolen from some other jit thread
(pgbench running single client with multiple unions of selects a-la
SELECT a, count(*), sum(b) FROM test WHERE c = 2 GROUP BY a) show some
slight performance differences, but nothing dramatic so far. LLVM 17
version produces the lowest latency, with faster generation, inlining
and optimization, but slower emission time. LLVM 12 version produces the
largest latencies with everything except emission timings being slower.
LLVM 15 is somewhere in between.

I'll continue reviewing and, for the records, attach adjustments I was
using for LLVM 17 (purely for testing, not taking into account other
versions), in case if I've missed something.