| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
| Cc: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, "Stefan Kaltenbrunner" <stefan(at)kaltenbrunner(dot)cc>, "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: compiler warnings on the buildfarm |
| Date: | 2007-07-12 22:34:23 |
| Message-ID: | 12802.1184279663@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> If it does constant propagation without handling overflow it could end up
> with:
> (olddatum >> 2 << 2) & 0x3FFFFFFFC
> note that in fact truncating the high two bits as the assembler did would in
> fact be the correct thing to do here which would explain why it doesn't cause
> any actual problems.
Good point, but I also note that the places Heikki saw were inside
loops. I think it might be some combination of the above and a loop
strength reduction optimization.
regards, tom lane
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