[Bug target/27827] [4.0/4.1/4.2 Regression] gcc 4 produces worse x87 code on all platforms than gcc 3

["whaley at cs dot utsa dot edu" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #29 from whaley at cs dot utsa dot edu  2006-07-04 13:15 -------
Guys,

The integer and fp differences do not appear to be strongly related.  In
particular, on my P4e, gcc 4's integer code is actually faster than gcc 3's. 
Further, if you look at the assemblies of the integer code, it does not have
the extra dependencies that gcc 4's x87 code has.  In integer, both gcc 3 and 4
explicitly do all loads to registers.  I haven't scoped it in detail, but the
main difference appears to be in scheduling, with gcc 3 performing a bunch of
loads, then a bunch of computations, and gcc 4 intermixing them more.

So, we'd need a new series of runs to see which integer schedule is better, but
the integer code should not be studied to solve the x87 problem.

Thanks,
Clint


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827