2013/3/27 Koehne Kai <[email protected]>
> > -----Original Message-----
> > From: Etienne Sandré-Chardonnal [mailto:[email protected]]
> > Sent: Wednesday, March 27, 2013 3:43 PM
> > To: [email protected]
> > Subject: Re: [Mingw-w64-public] Performance changes when switching to
> > 4.8.0
> >
> > I'm using the rubenvb with no "dw2" in the archive name, so I suppose I'm
> > using SJLJ in 32bit and SEH in 64bit?
>
> I guess so.
>
> > Can there be a 30% speed difference just due to SJLJ, even if I do not
> use any
> > exception handling in my code?
>
> Yes, actually I had measured about 25% slow down e.g. in creator startup,
> and for the test case in the bug report it's even 300%.
>
> The jumps implementing SJLJ are automatically added to any code block that
> _might_ throw, or propagate, an exception. So you don't have to have any
> try {} catch {} blocks to get the slowdown, I understood.
>
> > Other libs may use exceptions, but my app is
> > running my code 99% of the time, as libs are only used for GUI and during
> > initialization.
>
> Well, it's enough if you're using e.g. QtCore, which is compiled with
> exception handling enabled. Only if you do -fno-exceptions for all libs you
> should be on the safe side, performance wise.
>
> > What do I risk with dw2? I've read the main guidelines, but my
> understanding
> > of exception handling and stack frame unwinding is too short to
> understand
> > if this will impact my work.
>
> There are problems (crashes) with dwarf as soon as you actually use
> exceptions, and you want them to propagate to stacks not compiled with the
> same compiler. Also Jonathan Liu reported issues with
> LoadLibrary/FreeLibrary, see http://qt-project.org/wiki/MinGW-64-bit .
>
> Anyway, we plan to switch to a dwarf toolchain for official Qt packages
> with 5.1 onwards.
>
> Regards
>
> Kai
>
>
>
This pretty much sums everything up. It's also one of the reasons I provide
both versions for 32-bit.
It is pretty cool GCC beats MSVC. Although this is not the first time (see
the Blender MinGW-w64 builds).
If only someone from e.g. AMD would spend time in an open source
MSVC-compatible Windows exception handling/debug info code generation...
library... or something.
Ruben
>
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