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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 

(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      (personal mail) (CodeSourcery mail) (Bugzilla assignments and CCs)

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