On 09/10/2013 04:44 AM, Richard Biener wrote:
On Tue, Sep 10, 2013 at 10:11 AM, Jakub Jelinek <ja...@redhat.com> wrote:
On Tue, Sep 10, 2013 at 10:06:04AM +0200, David Brown wrote:
This last point is crucial. I haven't looked at the code in question,
but one point to check is how the functions are called. If they are
often called with constant values, then they may be very much simplified
due to constant propagation. Secondly, if a function is inlined, the
compiler has full knowledge of the effects of the function "call" and
can thus optimise better (keeping data in registers over the "call",
shuffling around loads and stores, etc.). Finally, if the functions are
called in loops or other time-critical code, it can be worth spending
more code section space for a faster result (but sometimes smaller code
is faster due to caches, branch prediction buffers, etc.).
The ideal situation is that LTO figures this out for you, and the code
At least until LTO keeps to end up with unusable or hardly usable debug
info, effectively requiring LTO for good compiler performance is a
non-starter. And, the inliner we have is not dumb, if it sees an inline
function, but it is too large, it will usually not inline it.
So, rather than counting the lines of inline functions in headers, IMHO it
is better to look at inliner's decisions about those functions, if it
never inlines them, then supposedly moving them out of line is reasonable.
I mostly agree. Though please also factor in IPA-CP - the reason that
get_addr_base_and_unit_offset_1 is inline is that it receives a callback
which in all call-sites is constant or NULL and optimizing that function
is cruical (it will be usually called once in each TU and thus either inlined
or cloned for IPA-CP).
Also the operand iterators are very important to optimize, so outlining
them is a non-starter.
There isn't much code I'd expect we want to put back into .c files instead
given that we now use C++ I'd expect more code to be moved into header
files because of the use of templates.
That's the way of life with C++ - you got what you wanted ;)
:-) Gonna be a lot of little inlines that is for sure.
I think its probably more worthwhile to focus on getting functions into
appropriate places than trying to make decisions about what should or
shouldn't be inlined at this point.
