Date: Wed, 28 Jan 2026 07:56:46 +0000
To: Matheus Alcantara <matheusssilv97@gmail.com>
From: Pierre Ducroquet <p.psql@pinaraf.info>
Cc: "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Subject: Re: [PATCH] llvmjit: always add the simplifycfg pass
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Hi

Here is a rebased version of the patch with a rewrite of the comment.
Thank you again for your previous review.
FYI, I've tried adding other passes but none had a similar benefits over co=
st ratio. The benefits could rather be in changing from O3 to an extensive =
list of passes.


Le jeudi 22 janvier 2026 =C3=A0 10:41 PM, Matheus Alcantara <matheusssilv97=
@gmail.com> a =C3=A9crit=C2=A0:

> On Thu Jan 22, 2026 at 5:27 PM -03, Pierre Ducroquet wrote:
>=20
> > > The patch needs a rebase due to e5d99b4d9ef.
> > >=20
> > > You've added the "simplifycfg" only when the "jit_optimize_above_cost=
"
> > > is not triggered which will use the default<O0> and mem2reg passes, t=
he
> > >=20
> > > default<O3> pass already include "simplifycfg"?
> > >=20
> > > With e5d99b4d9ef being committed, should we add "simplifycfg" when
> > > PGJIT_INLINE bit is set since it also use the default<O0> and mem2reg
> > >=20
> > > passes?
> >=20
> > Hi
> >=20
> > Thank you, here is a rebased version of the patch.
> > To answer your questions:
> > - O3 already includes simplifycfg, so no need to modify O3
> > - any code generated by our llvmjit provider, esp. tuple deforming, is =
heavily dependent on simplifycfg, so when O0 is the basis we should always =
add this pass
>=20
>=20
> Thanks for confirming.
>=20
> I did some benchmarks on some TPCH queries (1 and 4) and I got these
> results. Note that for these tests I set jit_optimize_above_cost=3D100000=
0
> so that it force to use the default<O0> pass with simplifycfg.
>=20
>=20
> Master Q1:
> Timing: Generation 1.553 ms (Deform 0.573 ms), Inlining 0.052 ms, Optimiz=
ation 95.571 ms, Emission 58.941 ms, Total 156.116 ms
> Execution Time: 38221.318 ms
>=20
> Patch Q1:
> Timing: Generation 1.477 ms (Deform 0.534 ms), Inlining 0.040 ms, Optimiz=
ation 95.364 ms, Emission 58.046 ms, Total 154.927 ms
> Execution Time: 38257.797 ms
>=20
> Master Q4:
> Timing: Generation 0.836 ms (Deform 0.309 ms), Inlining 0.086 ms, Optimiz=
ation 5.098 ms, Emission 6.963 ms, Total 12.983 ms
> Execution Time: 19512.134 ms
>=20
> Patch Q4:
> Timing: Generation 0.802 ms (Deform 0.294 ms), Inlining 0.090 ms, Optimiz=
ation 5.234 ms, Emission 6.521 ms, Total 12.648 ms
> Execution Time: 16051.483 ms
>=20
>=20
> For Q4 I see a small increase on Optimization phase but we have a good
> performance improvement on execution time. For Q1 the results are almost
> the same.
>=20
> I did not find any major regression using simplifycfg pass and I think
> that it make sense to enable since it generate better IR code for LLVM
> to compile without too much costs. +1 for this patch.
>=20
> Perhaps we could merge the comments on if/else block to include the
> simplifycfg, what do you think?
>=20
> + /*
> + * Determine the LLVM pass pipeline to use. For OPT3 we use the standard
> + * suite. For lower optimization levels, we explicitly include mem2reg t=
o
> + * promote stack variables, simplifycfg to clean up the control flow , a=
nd
> + * optionally the inliner if the flag is set. Note that default<O0> alre=
ady
>=20
> + * includes the always-inline pass.
> + */
> if (context->base.flags & PGJIT_OPT3)
>=20
> passes =3D "default<O3>";
>=20
> else if (context->base.flags & PGJIT_INLINE)
>=20
> - /* if doing inlining, but no expensive optimization, add inline pass */
> passes =3D "default<O0>,mem2reg,simplifycfg,inline";
>=20
> else
> - /* default<O0> includes always-inline pass */
>=20
> passes =3D "default<O0>,mem2reg,simplifycfg";
>=20
>=20
> --
> Matheus Alcantara
> EDB: https://www.enterprisedb.com
> 
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