pgsql: Expression evaluation based aggregate transition invocation.

Expression evaluation based aggregate transition invocation.

Previously aggregate transition and combination functions were invoked
by special case code in nodeAgg.c, evaluating input and filters
separately using the expression evaluation machinery. That turns out
to not be great for performance for several reasons:

- repeated expression evaluations have some cost
- the transition functions invocations are poorly predicted, as
commonly there are multiple aggregates in a query, resulting in the
same call-stack invoking different functions.
- filter and input computation had to be done separately
- the special case code made it hard to implement JITing of the whole
transition function invocation

Address this by building one large expression that computes input,
evaluates filters, and invokes transition functions.

This leads to moderate speedups in queries bottlenecked by aggregate
computations, and enables large speedups for similar cases once JITing
is done.

There's potential for further improvement:
- It'd be nice if we could simplify the somewhat expensive
aggstate->all_pergroups lookups.
- right now there's still an advance_transition_function invocation in
nodeAgg.c, leading to some code duplication.

Author: Andres Freund
Discussion: https://postgr.es/m/20170901064131.tazjxwus3k2w3ybh@alap3.anarazel.de

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/69c3936a1499b772a749ae629fc59b2d72722332

Modified Files
--------------
src/backend/executor/execExpr.c | 429 ++++++++++++++++-
src/backend/executor/execExprInterp.c | 356 +++++++++++++-
src/backend/executor/nodeAgg.c | 864 ++++------------------------------
src/include/executor/execExpr.h | 76 ++-
src/include/executor/executor.h | 4 +-
src/include/executor/nodeAgg.h | 284 +++++++++++
src/include/nodes/execnodes.h | 5 +-
src/tools/pgindent/typedefs.list | 1 +
8 files changed, 1230 insertions(+), 789 deletions(-)