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Message-ID: <4696A5F1.3010103@enterprisedb.com>
Date: Thu, 12 Jul 2007 23:06:41 +0100
From: Heikki Linnakangas <heikki@enterprisedb.com>
User-Agent: Icedove 1.5.0.10 (X11/20070329)
MIME-Version: 1.0
To: Alvaro Herrera <alvherre@commandprompt.com>
CC: Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>,
	Tom Lane <tgl@sss.pgh.pa.us>,
	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>
In-Reply-To: <20070712213806.GE22973@alvh.no-ip.org>
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Alvaro Herrera wrote:
> Heikki Linnakangas wrote:
>> Alvaro Herrera wrote:
>>> Stefan showed me via Jabber this warning:
>>> /tmp/ccM7MfqX.s: Assembler messages:
>>> /tmp/ccM7MfqX.s:703: Warning: 00000003fffffffc shortened to 
>>> 00000000fffffffc
>>> /tmp/ccM7MfqX.s:738: Warning: 00000003fffffffc shortened to 
>>> 00000000fffffffc
>>> He says that this comes from trgm_op.c file.  I don't get the warning
>>> myself obviously, so I started guessing.
>>> 3FFFFFFFC = 1111111111111111111111111111111100
>>>  FFFFFFFC =   11111111111111111111111111111100
>>> So the upper 2 bits are being lost (the second number is 32 bits wide).
>>> The only thing that I think is related is the usage of VARSIZE().  It
>>> looks like 0x3FFFFFFF (actual constant in the toast code) is shift two
>>> bits left.  I can see no such operation though.
>> The shift is in postgres.h, SET_VARSIZE_4B. I have no idea where that 
>> warning is coming from, though. What's the real source behind "ccM7MfqX.s"?
> 
> trgm_op.c
> 
> I'm not sure that the shift in SET_VARSIZE_4B is applicable here,
> because it would have to be passed a len of FFFFFFFF.

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++;
> 	}

Line 224:
> 	ptr = GETARR(trg);
> 	while (ptr - GETARR(trg) < ARRNELEM(trg))
> 	{
>>>>> 		pfree(DatumGetPointer(d[ptr - GETARR(trg)]));
> 		ptr++;
> 	}

The warning seems to be in related array indexing. If you replace ptr - 
GETARR(trg) with a constant, the warning goes away. But having "i = ptr 
- GETARR(trg)" in there doesn't give a warning.

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