Re: [PATCH] llvmjit: always add the simplifycfg pass

On Thu Jan 22, 2026 at 5:27 PM -03, Pierre Ducroquet wrote:
>> The patch needs a rebase due to e5d99b4d9ef.
>>
>> You've added the "simplifycfg" only when the "jit_optimize_above_cost"
>> is not triggered which will use the default<O0> and mem2reg passes, the
>>
>> default<O3> pass already include "simplifycfg"?
>>
>>
>> With e5d99b4d9ef being committed, should we add "simplifycfg" when
>> PGJIT_INLINE bit is set since it also use the default<O0> and mem2reg
>>
>> passes?
>
> Hi
>
> 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

Thanks for confirming.

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=1000000
so that it force to use the default<O0> pass with simplifycfg.

Master Q1:
Timing: Generation 1.553 ms (Deform 0.573 ms), Inlining 0.052 ms, Optimization 95.571 ms, Emission 58.941 ms, Total 156.116 ms
Execution Time: 38221.318 ms

Patch Q1:
Timing: Generation 1.477 ms (Deform 0.534 ms), Inlining 0.040 ms, Optimization 95.364 ms, Emission 58.046 ms, Total 154.927 ms
Execution Time: 38257.797 ms

Master Q4:
Timing: Generation 0.836 ms (Deform 0.309 ms), Inlining 0.086 ms, Optimization 5.098 ms, Emission 6.963 ms, Total 12.983 ms
Execution Time: 19512.134 ms

Patch Q4:
Timing: Generation 0.802 ms (Deform 0.294 ms), Inlining 0.090 ms, Optimization 5.234 ms, Emission 6.521 ms, Total 12.648 ms
Execution Time: 16051.483 ms

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.

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.

Perhaps we could merge the comments on if/else block to include the
simplifycfg, what do you think?

+ /*
+ * Determine the LLVM pass pipeline to use. For OPT3 we use the standard
+ * suite. For lower optimization levels, we explicitly include mem2reg to
+ * promote stack variables, simplifycfg to clean up the control flow , and
+ * optionally the inliner if the flag is set. Note that default<O0> already
+ * includes the always-inline pass.
+ */
if (context->base.flags & PGJIT_OPT3)
passes = "default<O3>";
else if (context->base.flags & PGJIT_INLINE)
- /* if doing inlining, but no expensive optimization, add inline pass */
passes = "default<O0>,mem2reg,simplifycfg,inline";
else
- /* default<O0> includes always-inline pass */
passes = "default<O0>,mem2reg,simplifycfg";

--
Matheus Alcantara
EDB: https://www.enterprisedb.com