Remove fls(), use pg_leftmost_one_pos32() instead.

Commit 4f658dc8 provided the traditional BSD fls() function in
src/port/fls.c so it could be used in several places.  Later we added a
bunch of similar facilities in pg_bitutils.h, based on compiler
builtins that map to hardware instructions.  It's a bit confusing to
have both 1-based and 0-based variants of this operation in use in
different parts of the tree, and neither is blessed by a standard.
Let's drop fls.c and the configure probe, and reuse the newer code.

Reviewed-by: David Rowley <dgrowleyml@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CA%2BhUKG%2B7dSX1XF8yFGmYk-%3D48dbjH2kmzZj16XvhbrWP-9BzRg%40mail.gmail.com

4 files changed, 18 insertions, 5 deletions

diff --git a/src/backend/access/hash/hashutil.c b/src/backend/access/hash/hashutil.c
index fe37bc47cbb..32822dbb6b9 100644
--- a/src/backend/access/hash/hashutil.c
+++ b/src/backend/access/hash/hashutil.c
@@ -436,7 +436,7 @@ _hash_get_oldblock_from_newbucket(Relation rel, Bucket new_bucket)
 	 * started.  Masking the most significant bit of new bucket would give us
 	 * old bucket.
 	 */
-	mask = (((uint32) 1) << (fls(new_bucket) - 1)) - 1;
+	mask = (((uint32) 1) << pg_leftmost_one_pos32(new_bucket)) - 1;
 	old_bucket = new_bucket & mask;
 
 	metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_READ, LH_META_PAGE);
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 028d9e16808..63f0f6b79c7 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -47,6 +47,7 @@
 #include "parser/parsetree.h"
 #include "partitioning/partbounds.h"
 #include "partitioning/partprune.h"
+#include "port/pg_bitutils.h"
 #include "rewrite/rewriteManip.h"
 #include "utils/lsyscache.h"
 
@@ -1491,7 +1492,7 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
 		if (enable_parallel_append)
 		{
 			parallel_workers = Max(parallel_workers,
-								   fls(list_length(live_childrels)));
+								   pg_leftmost_one_pos32(list_length(live_childrels)) + 1);
 			parallel_workers = Min(parallel_workers,
 								   max_parallel_workers_per_gather);
 		}
@@ -1542,7 +1543,7 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
 		 * the planned number of parallel workers.
 		 */
 		parallel_workers = Max(parallel_workers,
-							   fls(list_length(live_childrels)));
+							   pg_leftmost_one_pos32(list_length(live_childrels)) + 1);
 		parallel_workers = Min(parallel_workers,
 							   max_parallel_workers_per_gather);
 		Assert(parallel_workers > 0);
diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 2214920dea4..043181b586b 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -675,7 +675,7 @@ generate_union_paths(SetOperationStmt *op, PlannerInfo *root,
 		if (enable_parallel_append)
 		{
 			parallel_workers = Max(parallel_workers,
-								   fls(list_length(partial_pathlist)));
+								   pg_leftmost_one_pos32(list_length(partial_pathlist)) + 1);
 			parallel_workers = Min(parallel_workers,
 								   max_parallel_workers_per_gather);
 		}
diff --git a/src/backend/utils/mmgr/dsa.c b/src/backend/utils/mmgr/dsa.c
index b6cb8fa13dc..82376fde2d9 100644
--- a/src/backend/utils/mmgr/dsa.c
+++ b/src/backend/utils/mmgr/dsa.c
@@ -51,6 +51,7 @@
 #include "postgres.h"
 
 #include "port/atomics.h"
+#include "port/pg_bitutils.h"
 #include "storage/dsm.h"
 #include "storage/ipc.h"
 #include "storage/lwlock.h"
@@ -137,7 +138,18 @@ typedef size_t dsa_segment_index;
  * free pages?	There is no point in looking in segments in lower bins; they
  * definitely can't service a request for n free pages.
  */
-#define contiguous_pages_to_segment_bin(n) Min(fls(n), DSA_NUM_SEGMENT_BINS - 1)
+static inline size_t
+contiguous_pages_to_segment_bin(size_t n)
+{
+	size_t		bin;
+
+	if (n == 0)
+		bin = 0;
+	else
+		bin = pg_leftmost_one_pos_size_t(n) + 1;
+
+	return Min(bin, DSA_NUM_SEGMENT_BINS - 1);
+}
 
 /* Macros for access to locks. */
 #define DSA_AREA_LOCK(area) (&area->control->lock)