llvm dev - Sep 2009 - [LLVMdev] FYI: Phoronix GCC vs. LLVM-GCC benchmarks

Since we are in the area, what *should* O1 do?

It's basically good for nothing, since it doesn't tune for size or
performance. The only good I personally ever have for it is once in a
while there is a miscompile at -O1 which narrows the problem.

Would it be crazy to make -O1 equivalent to -Os?

 - Daniel

On Wednesday, September 16, 2009, Chris Lattner <clattner at apple.com>
wrote:
>
> On Sep 16, 2009, at 10:05 AM, Stefano Delli Ponti wrote:
>
>> Chris Lattner:
>>> Comparing -O3 (and even -O4) is interesting, but we want all
>>> optimization levels to perform better than GCC :).  Lots of people
>>> use  -O2 and -Os, so comparing against other compiler's -O2 and
-Os
>>> levels  is just as interesting as comparing -O3 vs -O3.
>>
>> My thinking was that, for instance, -02 for GCC and -02 for LLVM(-
>> GCC) do not necessarily mean the same thing, they may be not /
>> commensurable/.
>> But perhaps, my ignorance, you are saying that they _are_, that LLVM
>> assigns the same types of optimizations as GCC to the different
>> levels.
>
> Right, we want them to be roughly comparable.
>
> O0 -> best debug experience, fastest compile times.
> O2 -> optimize without bloating the code too much and without burning
> *too* many cycles.
> O3 -> take more time and produce fatter code to get faster code.
>
> O1 is something of a wasteland with no clear purpose :)
>
> -Chris
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On Sep 16, 2009, at 10:36 AM, Daniel Dunbar wrote:
> Since we are in the area, what *should* O1 do?
>
> It's basically good for nothing, since it doesn't tune for size or
> performance. The only good I personally ever have for it is once in a
> while there is a miscompile at -O1 which narrows the problem.
>
> Would it be crazy to make -O1 equivalent to -Os?
I've always used O1 for a quick cleanup so that my debug code doesn't  
completely suck, but hasn't been optimized into oblivion for gdb.   
Also makes looking at the resultant assembly dumps fairly easy.

But yes, that'd be crazy :)

-eric

Daniel Dunbar <daniel at zuster.org> writes:
> Since we are in the area, what *should* O1 do?
"Try to produce fast code but do not apply transformations that makes
debugging hard"

-- 
Óscar

On Sep 16, 2009, at 10:36 AM, Daniel Dunbar wrote:
> Since we are in the area, what *should* O1 do?
>
> It's basically good for nothing, since it doesn't tune for size or
> performance. The only good I personally ever have for it is once in a
> while there is a miscompile at -O1 which narrows the problem.
>
> Would it be crazy to make -O1 equivalent to -Os?
That works for me! :-)

2009/9/16 Eric Christopher <echristo at
apple.com>:
> Also makes looking at the resultant assembly dumps fairly easy.
>
> But yes, that'd be crazy :)
My father prefers that to writing assembly code directly. Seems like a
pretty normal thing to do...

Crazy is producing assembly directly, which he still does most of the time... ;)

cheers,
--renato

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On Wed, Sep 16, 2009 at 10:52 AM, Eric Christopher <echristo at apple.com>
wrote:
> On Sep 16, 2009, at 10:36 AM, Daniel Dunbar wrote:
>> Since we are in the area, what *should* O1 do?
>>
>> It's basically good for nothing, since it doesn't tune for size
or
>> performance. The only good I personally ever have for it is once in a
>> while there is a miscompile at -O1 which narrows the problem.
>>
>> Would it be crazy to make -O1 equivalent to -Os?
>
> I've always used O1 for a quick cleanup so that my debug code
doesn't
> completely suck, but hasn't been optimized into oblivion for gdb.  Also
> makes looking at the resultant assembly dumps fairly easy.
If this is from the compiler programmer perspective, we have better
tools for that. If this is from the user perspective, currently they
all are bad with LLVM for the former, and we should similarly fix all
of them. :)
> But yes, that'd be crazy :)
Was that a -1 on doing it, though? :)

 - Daniel