On 07/01/2010 02:27 PM, Richard Guenther wrote:
On Thu, Jul 1, 2010 at 10:29 PM, Taras Glek<tg...@mozilla.com> wrote:
On 06/30/2010 03:06 PM, Jan Hubicka wrote:
If you can find actual simple examples where -Os is losing size and speed
we can try
to do something about them.
According to our code size reports, inlining is completely screwed for C++
wrapper classes like ones often used for smart pointers, arrays, etc. See
http://people.mozilla.com/~tglek/codesize45.txt
Would be really nice if this could be fixed in 4.5. It's tricky for us to
switch to 4.5 otherwise.
The following code inlines as expected under -Os in 4.4. It also inlines
properly with -O1+ in 4.5. But it generates giant bloated code under -Os in
4.5.
class Container {
public:
Container() {
member = new int;
}
void cleanup() {
delete member;
member = 0;
}
int value() {
return *member;
}
~Container() {
cleanup();
}
private:
int *member;
};
int gimme() {
Container m;
return m.value();
}
Without looking I bet the issue here is call_cost at -Os (which is 1).
In the above example we are only not inlining the constructor, which
is estimated as size 2 (a function call with one (constant) parameter).
Inlining that enlarges the caller as we'd replace a call without an
argument with one with an argument.
So the inlining decision isn't too bad for -Os here (which means
your testcase isn't a good representative of what is the issue).
You are right. I tried a -finline-limit=50 flag that we used for gcc 4.1
& 4.2 and that appears to bring performance to slightly above 4.3 levels
with -Os.
However, this testcase that was most obvious regression from reading the
above code size report. Seems like a pretty serious regression given that
size inline.o
Returns 158 with -Os and 93 with -O1.
This doesn't get "fixed" by -finline-limit=50
Taras
