Re: compiler warnings on the buildfarm

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