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

configure

@@ -16771,19 +16771,6 @@ esac
 
 fi
 
-ac_fn_c_check_func "$LINENO" "fls" "ac_cv_func_fls"
-if test "x$ac_cv_func_fls" = xyes; then :
-  $as_echo "#define HAVE_FLS 1" >>confdefs.h
-
-else
-  case " $LIBOBJS " in
-  *" fls.$ac_objext "* ) ;;
-  *) LIBOBJS="$LIBOBJS fls.$ac_objext"
- ;;
-esac
-
-fi
-
 ac_fn_c_check_func "$LINENO" "getopt" "ac_cv_func_getopt"
 if test "x$ac_cv_func_getopt" = xyes; then :
   $as_echo "#define HAVE_GETOPT 1" >>confdefs.h

configure.ac

@@ -1911,7 +1911,6 @@ fi
 AC_REPLACE_FUNCS(m4_normalize([
 	dlopen
 	explicit_bzero
-	fls
 	getopt
 	getpeereid
 	getrusage

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);

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);

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);
 		}

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)

src/include/pg_config.h.in

@@ -191,9 +191,6 @@
 /* Define to 1 if you have the `fdatasync' function. */
 #undef HAVE_FDATASYNC
 
-/* Define to 1 if you have the `fls' function. */
-#undef HAVE_FLS
-
 /* Define to 1 if fseeko (and presumably ftello) exists and is declared. */
 #undef HAVE_FSEEKO
 

src/include/port.h

@@ -366,10 +366,6 @@ extern int	gettimeofday(struct timeval *tp, struct timezone *tzp);
 #define pgoff_t off_t
 #endif
 
-#ifndef HAVE_FLS
-extern int	fls(int mask);
-#endif
-
 #ifndef HAVE_GETPEEREID
 /* On Windows, Perl might have incompatible definitions of uid_t and gid_t. */
 #ifndef PLPERL_HAVE_UID_GID

src/port/fls.c

@@ -1,64 +0,0 @@
-/*-------------------------------------------------------------------------
- *
- * fls.c
- *	  finds the last (most significant) bit that is set
- *
- * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
- *
- *
- * IDENTIFICATION
- *	  src/port/fls.c
- *
- * This file was taken from FreeBSD to provide an implementation of fls()
- * for platforms that lack it.  Note that the operating system's version may
- * be substantially more efficient than ours, since some platforms have an
- * assembly instruction that does exactly this.
- *
- * The FreeBSD copyright terms follow.
- */
-
-/*-
- * Copyright (c) 1990, 1993
- *	The Regents of the University of California.  All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *	  notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *	  notice, this list of conditions and the following disclaimer in the
- *	  documentation and/or other materials provided with the distribution.
- * 4. Neither the name of the University nor the names of its contributors
- *	  may be used to endorse or promote products derived from this software
- *	  without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#include "c.h"
-
-/*
- * Find Last Set bit
- */
-int
-fls(int mask)
-{
-	int			bit;
-
-	if (mask == 0)
-		return (0);
-	for (bit = 1; mask != 1; bit++)
-		mask = (unsigned int) mask >> 1;
-	return (bit);
-}

src/tools/msvc/Mkvcbuild.pm

@@ -99,7 +99,7 @@ sub mkvcbuild
 	$solution = CreateSolution($vsVersion, $config);
 
 	our @pgportfiles = qw(
-	  chklocale.c explicit_bzero.c fls.c fdatasync.c
+	  chklocale.c explicit_bzero.c fdatasync.c
 	  getpeereid.c getrusage.c inet_aton.c
 	  getaddrinfo.c gettimeofday.c inet_net_ntop.c kill.c open.c
 	  snprintf.c strlcat.c strlcpy.c dirmod.c noblock.c path.c

src/tools/msvc/Solution.pm

@@ -258,7 +258,6 @@ sub GenerateFiles
 		HAVE_EXECINFO_H                             => undef,
 		HAVE_EXPLICIT_BZERO                         => undef,
 		HAVE_FDATASYNC                              => 1,
-		HAVE_FLS                                    => undef,
 		HAVE_FSEEKO                                 => 1,
 		HAVE_FUNCNAME__FUNC                         => undef,
 		HAVE_FUNCNAME__FUNCTION                     => 1,