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Message-ID: <4696B045.8080405@enterprisedb.com>
Date: Thu, 12 Jul 2007 23:50:45 +0100
From: Heikki Linnakangas <heikki@enterprisedb.com>
User-Agent: Icedove 1.5.0.10 (X11/20070329)
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: Alvaro Herrera <alvherre@commandprompt.com>,
	Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: compiler warnings on the buildfarm
References: <46962BBD.5000108@kaltenbrunner.cc>
	<17428.1184249229@sss.pgh.pa.us>
	<469653BA.2040004@kaltenbrunner.cc>
	<20070712211918.GD22973@alvh.no-ip.org>
	<46969C98.60207@enterprisedb.com>
	<20070712213806.GE22973@alvh.no-ip.org>
	<4696A5F1.3010103@enterprisedb.com>
	<12639.1184279380@sss.pgh.pa.us>
In-Reply-To: <12639.1184279380@sss.pgh.pa.us>
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Tom Lane wrote:
> Heikki Linnakangas <heikki@enterprisedb.com> writes:
>> Hmm. It looks like I get that warning on my laptop as well. I tracked it 
>> down to these two places:
> 
>> Line 209:
>>> while (ptr - GETARR(trg) < ARRNELEM(trg))
>>> {
>>> 	text	   *item = (text *) palloc(VARHDRSZ + 3);
>>> 	
>>> 	SET_VARSIZE(item, VARHDRSZ + 3);
>>> 	CPTRGM(VARDATA(item), ptr);
>>>>> 	d[ptr - GETARR(trg)] = PointerGetDatum(item);
>>> 	ptr++;
>>> }
> 
> I'll betcha the compiler is trying to optimize the repeated calculations
> of "ptr - GETARR(trg)" into a separate variable that it increments along
> with ptr.  Maybe it is getting it wrong, or maybe the assembler is just
> confused.  Does the warning go away if you dial down the -O level?

FWIW, this patch makes the warnings go away, and makes the code a little 
bit more readable as well. It would be nice to understand why exactly 
it's complaining, though.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

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Index: trgm_op.c
===================================================================
RCS file: /home/hlinnaka/pgcvsrepository/pgsql/contrib/pg_trgm/trgm_op.c,v
retrieving revision 1.8
diff -c -r1.8 trgm_op.c
*** trgm_op.c	28 Feb 2007 22:44:38 -0000	1.8
--- trgm_op.c	12 Jul 2007 22:28:43 -0000
***************
*** 194,212 ****
  	Datum	   *d;
  	ArrayType  *a;
  	trgm	   *ptr;
  
  	trg = generate_trgm(VARDATA(in), VARSIZE(in) - VARHDRSZ);
  	d = (Datum *) palloc(sizeof(Datum) * (1 + ARRNELEM(trg)));
  
! 	ptr = GETARR(trg);
! 	while (ptr - GETARR(trg) < ARRNELEM(trg))
  	{
  		text	   *item = (text *) palloc(VARHDRSZ + 3);
  
  		SET_VARSIZE(item, VARHDRSZ + 3);
  		CPTRGM(VARDATA(item), ptr);
! 		d[ptr - GETARR(trg)] = PointerGetDatum(item);
! 		ptr++;
  	}
  
  	a = construct_array(
--- 194,211 ----
  	Datum	   *d;
  	ArrayType  *a;
  	trgm	   *ptr;
+ 	int			i;
  
  	trg = generate_trgm(VARDATA(in), VARSIZE(in) - VARHDRSZ);
  	d = (Datum *) palloc(sizeof(Datum) * (1 + ARRNELEM(trg)));
  
! 	for (i = 0, ptr = GETARR(trg); i < ARRNELEM(trg); i++, ptr++)
  	{
  		text	   *item = (text *) palloc(VARHDRSZ + 3);
  
  		SET_VARSIZE(item, VARHDRSZ + 3);
  		CPTRGM(VARDATA(item), ptr);
! 		d[i] = PointerGetDatum(item);
  	}
  
  	a = construct_array(
***************
*** 218,229 ****
  						'i'
  		);
  
! 	ptr = GETARR(trg);
! 	while (ptr - GETARR(trg) < ARRNELEM(trg))
! 	{
! 		pfree(DatumGetPointer(d[ptr - GETARR(trg)]));
! 		ptr++;
! 	}
  
  	pfree(d);
  	pfree(trg);
--- 217,224 ----
  						'i'
  		);
  
! 	for (i = 0; i < ARRNELEM(trg); i++)
! 		pfree(DatumGetPointer(d[i]));
  
  	pfree(d);
  	pfree(trg);

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