#ifdef out assorted unused GEQO code.

I'd always assumed that backend/optimizer/geqo/'s remarkably poor
showing on code coverage metrics was because we weren't exercising
it much in the regression tests.  But it turns out that a good chunk
of the problem is that there's a bunch of code that is physically
unreachable (because the calls to it are #ifdef'd out in geqo_main.c)
but is being built anyway.  Making the called code have #if guards
similar to the calling code saves a couple of kilobytes of executable
size and should make the coverage numbers more reflective of reality.

It's arguable that we should just delete all the unused recombination
mechanisms altogether, but I didn't feel a need to go that far today.

src/backend/optimizer/geqo/geqo_cx.c

@@ -38,6 +38,7 @@
 #include "optimizer/geqo_recombination.h"
 #include "optimizer/geqo_random.h"
 
+#if defined(CX)
 
 /* cx
  *
@@ -119,3 +120,5 @@ cx(PlannerInfo *root, Gene *tour1, Gene *tour2, Gene *offspring,
 
 	return num_diffs;
 }
+
+#endif   /* defined(CX) */

src/backend/optimizer/geqo/geqo_erx.c

@@ -35,6 +35,7 @@
 #include "optimizer/geqo_recombination.h"
 #include "optimizer/geqo_random.h"
 
+#if defined(ERX)
 
 static int	gimme_edge(PlannerInfo *root, Gene gene1, Gene gene2, Edge *edge_table);
 static void remove_gene(PlannerInfo *root, Gene gene, Edge edge, Edge *edge_table);
@@ -466,3 +467,5 @@ edge_failure(PlannerInfo *root, Gene *gene, int index, Edge *edge_table, int num
 	elog(ERROR, "no edge found");
 	return 0;					/* to keep the compiler quiet */
 }
+
+#endif   /* defined(ERX) */

src/backend/optimizer/geqo/geqo_main.c

@@ -46,14 +46,14 @@ double		Geqo_seed;
 static int	gimme_pool_size(int nr_rel);
 static int	gimme_number_generations(int pool_size);
 
-/* define edge recombination crossover [ERX] per default */
+/* complain if no recombination mechanism is #define'd */
 #if !defined(ERX) && \
 	!defined(PMX) && \
 	!defined(CX)  && \
 	!defined(PX)  && \
 	!defined(OX1) && \
 	!defined(OX2)
-#define ERX
+#error "must choose one GEQO recombination mechanism in geqo.h"
 #endif
 
 

src/backend/optimizer/geqo/geqo_mutation.c

@@ -35,6 +35,8 @@
 #include "optimizer/geqo_mutation.h"
 #include "optimizer/geqo_random.h"
 
+#if defined(CX)					/* currently used only in CX mode */
+
 void
 geqo_mutation(PlannerInfo *root, Gene *tour, int num_gene)
 {
@@ -60,3 +62,5 @@ geqo_mutation(PlannerInfo *root, Gene *tour, int num_gene)
 		num_swaps -= 1;
 	}
 }
+
+#endif   /* defined(CX) */

src/backend/optimizer/geqo/geqo_ox1.c

@@ -37,6 +37,7 @@
 #include "optimizer/geqo_random.h"
 #include "optimizer/geqo_recombination.h"
 
+#if defined(OX1)
 
 /* ox1
  *
@@ -90,3 +91,5 @@ ox1(PlannerInfo *root, Gene *tour1, Gene *tour2, Gene *offspring, int num_gene,
 	}
 
 }
+
+#endif   /* defined(OX1) */

src/backend/optimizer/geqo/geqo_ox2.c

@@ -37,6 +37,7 @@
 #include "optimizer/geqo_random.h"
 #include "optimizer/geqo_recombination.h"
 
+#if defined(OX2)
 
 /* ox2
  *
@@ -107,3 +108,5 @@ ox2(PlannerInfo *root, Gene *tour1, Gene *tour2, Gene *offspring, int num_gene,
 	}
 
 }
+
+#endif   /* defined(OX2) */

src/backend/optimizer/geqo/geqo_pmx.c

@@ -37,6 +37,7 @@
 #include "optimizer/geqo_random.h"
 #include "optimizer/geqo_recombination.h"
 
+#if defined(PMX)
 
 /* pmx
  *
@@ -219,3 +220,5 @@ pmx(PlannerInfo *root, Gene *tour1, Gene *tour2, Gene *offspring, int num_gene)
 	pfree(indx);
 	pfree(check_list);
 }
+
+#endif   /* defined(PMX) */

src/backend/optimizer/geqo/geqo_px.c

@@ -37,6 +37,7 @@
 #include "optimizer/geqo_random.h"
 #include "optimizer/geqo_recombination.h"
 
+#if defined(PX)
 
 /* px
  *
@@ -105,3 +106,5 @@ px(PlannerInfo *root, Gene *tour1, Gene *tour2, Gene *offspring, int num_gene,
 	}
 
 }
+
+#endif   /* defined(PX) */

src/backend/optimizer/geqo/geqo_recombination.c

@@ -58,6 +58,9 @@ init_tour(PlannerInfo *root, Gene *tour, int num_gene)
 	}
 }
 
+/* city table is used in these recombination methods: */
+#if defined(CX) || defined(PX) || defined(OX1) || defined(OX2)
+
 /* alloc_city_table
  *
  *	 allocate memory for city table
@@ -85,3 +88,5 @@ free_city_table(PlannerInfo *root, City *city_table)
 {
 	pfree(city_table);
 }
+
+#endif   /* CX || PX || OX1 || OX2 */

src/include/optimizer/geqo.h

@@ -31,7 +31,7 @@
  #define GEQO_DEBUG
  */
 
-/* recombination mechanism */
+/* choose one recombination mechanism here */
 /*
  #define ERX
  #define PMX