Interval regression test failing with -march=pentium4

I'm compiling postgresql 8.1.3 with these gcc flags: -march=pentium4 -O3

The compilation ends correctly but the interval regression test fails.
This is the diff file:

=====================================================================

*** ./expected/interval.out Thu Mar 23 15:38:42 2006
--- ./results/interval.out Thu Mar 23 16:16:06 2006
***************
*** 218,224 ****
select avg(f1) from interval_tbl;
avg
-------------------------------------------------
! @ 4 years 1 mon 9 days 28 hours 18 mins 23 secs
(1 row)

-- test long interval input
--- 218,224 ----
select avg(f1) from interval_tbl;
avg
-------------------------------------------------
! @ 4 years 1 mon 10 days 4 hours 18 mins 23 secs
(1 row)

-- test long interval input

======================================================================

If i compile the -march=i586 the regression test reports no problems.
Any tips?

Thank you,

Doct. Eng. Denis Gasparin
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Edistar Srl