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Re: Enable -funit-at-a-time at -O1
On Thu, 23 Jun 2005, Giovanni Bajo wrote:
> Just for information, what's the roadmap towards enabling unit-at-a-time by
> default in C (as it is in C++)? What is missing?
Nothing is in the way of enabling it by default (though compile-time
performance at -O0 might get slightly worse). The useful thing would be
removing non-unit-at-a-time mode altogether. That's waiting on preserving
the order of toplevel asms, functions and variables (possibly under a new
option also called -fno-unit-at-a-time, possibly whenever a toplevel asm
is seen) for C, for which there is a partial patch
<http://gcc.gnu.org/ml/gcc-patches/2005-04//msg01102.html>.
(As a *theoretical* matter you might say code shouldn't use toplevel asms
that way. As a *practical* matter, preserving declaration and asm order
for existing users of -fno-unit-at-a-time (and disabling any other
optimizations that prove problematic for such users on a case-by-case
basis) allows making unit-at-a-time always on without immediately breaking
a lot of code. You can always clean up crtstuff.c and deprecate
-fno-unit-at-a-time later if desired.)
--
Joseph S. Myers http://www.srcf.ucam.org/~jsm28/gcc/
jsm@polyomino.org.uk (personal mail)
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