Improve various places that double the size of a buffer

Several places were performing a tight loop to determine the first power
of 2 number that's > or >= the required memory.  Instead of using a loop
for that, we can use pg_nextpower2_32 or pg_nextpower2_64.  When we need a
power of 2 number equal to or greater than a given amount, we just pass
the amount to the nextpower2 function.  When we need a power of 2 greater
than the amount, we just pass the amount + 1.

Additionally, in tsearch there were a couple of locations that were
performing a while loop when a simple "if" would have done.  In both of
these locations only 1 item is being added, so the loop could only have
ever iterated once.  Changing the loop into an if statement makes the code
very slightly more optimal as the condition is checked once rather than
twice.

There are quite a few remaining locations that increase the size of the
buffer in the following form:

  while (reqsize >= buflen)
  {
     buflen *= 2;
     buf = repalloc(buf, buflen);
  }

These are not touched in this commit.  repalloc will error out for sizes
larger than MaxAllocSize.  Changing these to use pg_nextpower2_32 would
remove the chance of that error being raised.  It's unclear from the code
if the sizes could ever become that large, so err on the side of caution.

Discussion: https://postgr.es/m/CAApHDvp=tns7RL4PH0ZR0M+M-YFLquK7218x=0B_zO+DbOma+w@mail.gmail.com
Reviewed-by: Zhihong Yu

Author: david-rowley

src/backend/parser/scan.l

@@ -39,6 +39,7 @@
 #include "parser/gramparse.h"
 #include "parser/parser.h"		/* only needed for GUC variables */
 #include "parser/scansup.h"
+#include "port/pg_bitutils.h"
 #include "mb/pg_wchar.h"
 }
 
@@ -1253,10 +1254,7 @@ addlit(char *ytext, int yleng, core_yyscan_t yyscanner)
 	/* enlarge buffer if needed */
 	if ((yyextra->literallen + yleng) >= yyextra->literalalloc)
 	{
-		do
-		{
-			yyextra->literalalloc *= 2;
-		} while ((yyextra->literallen + yleng) >= yyextra->literalalloc);
+		yyextra->literalalloc = pg_nextpower2_32(yyextra->literallen + yleng + 1);
 		yyextra->literalbuf = (char *) repalloc(yyextra->literalbuf,
 												yyextra->literalalloc);
 	}

src/backend/storage/ipc/shm_mq.c

@@ -20,6 +20,7 @@
 
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "port/pg_bitutils.h"
 #include "postmaster/bgworker.h"
 #include "storage/procsignal.h"
 #include "storage/shm_mq.h"
@@ -720,14 +721,17 @@ shm_mq_receive(shm_mq_handle *mqh, Size *nbytesp, void **datap, bool nowait)
 		 */
 		if (mqh->mqh_buflen < nbytes)
 		{
-			Size		newbuflen = Max(mqh->mqh_buflen, MQH_INITIAL_BUFSIZE);
+			Size		newbuflen;
 
 			/*
-			 * Double the buffer size until the payload fits, but limit to
-			 * MaxAllocSize.
+			 * Increase size to the next power of 2 that's >= nbytes, but
+			 * limit to MaxAllocSize.
 			 */
-			while (newbuflen < nbytes)
-				newbuflen *= 2;
+#if SIZEOF_SIZE_T == 4
+			newbuflen = pg_nextpower2_32(nbytes);
+#else
+			newbuflen = pg_nextpower2_64(nbytes);
+#endif
 			newbuflen = Min(newbuflen, MaxAllocSize);
 
 			if (mqh->mqh_buffer != NULL)

src/backend/storage/lmgr/lwlock.c

@@ -79,6 +79,7 @@
 #include "miscadmin.h"
 #include "pg_trace.h"
 #include "pgstat.h"
+#include "port/pg_bitutils.h"
 #include "postmaster/postmaster.h"
 #include "replication/slot.h"
 #include "storage/ipc.h"
@@ -659,9 +660,7 @@ LWLockRegisterTranche(int tranche_id, const char *tranche_name)
 	{
 		int			newalloc;
 
-		newalloc = Max(LWLockTrancheNamesAllocated, 8);
-		while (newalloc <= tranche_id)
-			newalloc *= 2;
+		newalloc = pg_nextpower2_32(Max(8, tranche_id + 1));
 
 		if (LWLockTrancheNames == NULL)
 			LWLockTrancheNames = (const char **)
@@ -715,10 +714,7 @@ RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks)
 
 	if (NamedLWLockTrancheRequests >= NamedLWLockTrancheRequestsAllocated)
 	{
-		int			i = NamedLWLockTrancheRequestsAllocated;
-
-		while (i <= NamedLWLockTrancheRequests)
-			i *= 2;
+		int			i = pg_nextpower2_32(NamedLWLockTrancheRequests + 1);
 
 		NamedLWLockTrancheRequestArray = (NamedLWLockTrancheRequest *)
 			repalloc(NamedLWLockTrancheRequestArray,

src/backend/tsearch/spell.c

@@ -1600,7 +1600,8 @@ MergeAffix(IspellDict *Conf, int a1, int a2)
 	else if (*Conf->AffixData[a2] == '\0')
 		return a1;
 
-	while (Conf->nAffixData + 1 >= Conf->lenAffixData)
+	/* Double the size of AffixData if there's not enough space */
+	if (Conf->nAffixData + 1 >= Conf->lenAffixData)
 	{
 		Conf->lenAffixData *= 2;
 		Conf->AffixData = (char **) repalloc(Conf->AffixData,

src/backend/tsearch/ts_parse.c

@@ -436,7 +436,7 @@ parsetext(Oid cfgId, ParsedText *prs, char *buf, int buflen)
 static void
 hladdword(HeadlineParsedText *prs, char *buf, int buflen, int type)
 {
-	while (prs->curwords >= prs->lenwords)
+	if (prs->curwords >= prs->lenwords)
 	{
 		prs->lenwords *= 2;
 		prs->words = (HeadlineWordEntry *) repalloc((void *) prs->words, prs->lenwords * sizeof(HeadlineWordEntry));

src/backend/utils/cache/inval.c

@@ -106,6 +106,7 @@
 #include "catalog/catalog.h"
 #include "catalog/pg_constraint.h"
 #include "miscadmin.h"
+#include "port/pg_bitutils.h"
 #include "storage/sinval.h"
 #include "storage/smgr.h"
 #include "utils/catcache.h"
@@ -799,8 +800,7 @@ MakeSharedInvalidMessagesArray(const SharedInvalidationMessage *msgs, int n)
 
 	if ((numSharedInvalidMessagesArray + n) > maxSharedInvalidMessagesArray)
 	{
-		while ((numSharedInvalidMessagesArray + n) > maxSharedInvalidMessagesArray)
-			maxSharedInvalidMessagesArray *= 2;
+		maxSharedInvalidMessagesArray = pg_nextpower2_32(numSharedInvalidMessagesArray + n);
 
 		SharedInvalidMessagesArray = repalloc(SharedInvalidMessagesArray,
 											  maxSharedInvalidMessagesArray

src/backend/utils/cache/typcache.c

@@ -60,6 +60,7 @@
 #include "executor/executor.h"
 #include "lib/dshash.h"
 #include "optimizer/optimizer.h"
+#include "port/pg_bitutils.h"
 #include "storage/lwlock.h"
 #include "utils/builtins.h"
 #include "utils/catcache.h"
@@ -1708,10 +1709,7 @@ ensure_record_cache_typmod_slot_exists(int32 typmod)
 
 	if (typmod >= RecordCacheArrayLen)
 	{
-		int32		newlen = RecordCacheArrayLen * 2;
-
-		while (typmod >= newlen)
-			newlen *= 2;
+		int32		newlen = pg_nextpower2_32(typmod + 1);
 
 		RecordCacheArray = (TupleDesc *) repalloc(RecordCacheArray,
 												  newlen * sizeof(TupleDesc));