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Until now we generated an ExprState for each parameter to a SubPlan and evaluated them one-by-one ExecScanSubPlan. That's sub-optimal as creating lots of small ExprStates a) makes JIT compilation more expensive b) wastes memory c) is a bit slower to execute This commit arranges to evaluate parameters to a SubPlan as part of the ExprState referencing a SubPlan, using the new EEOP_PARAM_SET expression step. We emit one EEOP_PARAM_SET for each argument to a subplan, just before the EEOP_SUBPLAN step. It likely is worth using EEOP_PARAM_SET in other places as well, e.g. for SubPlan outputs, nestloop parameters and - more ambitiously - to get rid of ExprContext->domainValue/caseValue/ecxt_agg*. But that's for later. Author: Andres Freund <andres@anarazel.de> Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Reviewed-by: Alena Rybakina <lena.ribackina@yandex.ru> Discussion: https://postgr.es/m/20230225214401.346ancgjqc3zmvek@awork3.anarazel.de