Basic planner and executor integration for JIT.

This adds simple cost based plan time decision about whether JIT
should be performed. jit_above_cost, jit_optimize_above_cost are
compared with the total cost of a plan, and if the cost is above them
JIT is performed / optimization is performed respectively.

For that PlannedStmt and EState have a jitFlags (es_jit_flags) field
that stores information about what JIT operations should be performed.

EState now also has a new es_jit field, which can store a
JitContext. When there are no errors the context is released in
standard_ExecutorEnd().

It is likely that the default values for jit_[optimize_]above_cost
will need to be adapted further, but in my test these values seem to
work reasonably.

Author: Andres Freund, with feedback by Peter Eisentraut
Discussion: https://postgr.es/m/20170901064131.tazjxwus3k2w3ybh@alap3.anarazel.de

src/include/nodes/execnodes.h

@@ -528,6 +528,14 @@ typedef struct EState
 
 	/* The per-query shared memory area to use for parallel execution. */
 	struct dsa_area *es_query_dsa;
+
+	/*
+	 * JIT information. es_jit_flags indicates whether JIT should be performed
+	 * and with which options.  es_jit is created on-demand when JITing is
+	 * performed.
+	 */
+	int			es_jit_flags;
+	struct JitContext *es_jit;
 } EState;
 
 

src/include/nodes/plannodes.h

@@ -58,6 +58,8 @@ typedef struct PlannedStmt
 
 	bool		parallelModeNeeded; /* parallel mode required to execute? */
 
+	int			jitFlags;		/* which forms of JIT should be performed */
+
 	struct Plan *planTree;		/* tree of Plan nodes */
 
 	List	   *rtable;			/* list of RangeTblEntry nodes */