http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37273
Jeffrey A. Law <law at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2011.01.10 18:30:58
CC| |law at redhat dot com
Ever Confirmed|0 |1
--- Comment #4 from Jeffrey A. Law <law at redhat dot com> 2011-01-10 18:30:58
UTC ---
The issue I see here is IRA decides it is cheaper to allocate "ext" into a
call-clobbered register (an asm makes all call-saved registers conflict with
the pseudo holding "ext").
So with "ext" in a call-clobbered hard register, caller-saves then realizes the
value is live across calls and saves/restores it appropriately.
Regardless of whether or not the pseudo is allocated or not to a call clobbered
register we're going to be loading it from memory (either the caller-save slot
or the constant pool).
However, when allocated to a call-clobbered register, we have an extra store
(to initialize the caller-save slot) and additional stack space. So in theory
we ought to be able to easily determine that allocating a call-clobbered hard
reg for this value isn't a win.
I'm still poking.
