Subject: Re: gcc-dw2? or fast sjlj-exceptions EH
From: Tatsuro MATSUOKA <[email-masked]>
To: Eric Blake <[email-masked]>
Cc: [email-masked], [email-masked]
Date: Wed, 12 Sep 2007 12:58:53 +0900
List-Id: <cygwin.cygwin.com>

Dear Eric

>I think you are misunderstanding a fundamental concept.  sjlj exception
>handling is inherently slower than stack-tracing exception handling,
>because it must assume the worst and store the entire stack state (the
>'sj' or setjump) prior to any call site where an exception might occur,
>whether or not an exception actually happens (the 'lj' or longjump part).
> Dwarf error handling, on the other hand, is a form of stack-tracing,
>where there is NO penalty UNLESS there was an exception.  Exception
>handling is slower, because it must crawl backwards through the stack to
>find all catch points with handlers to run, but more efficient when there
>is no exception because you don't waste time saving state that never gets
>jumped to.

At previous mail time I felt that I understood the everything.
However, I cannot understand the sjlj-exception was adopted in the 
cygwin gcc and mingw gcc of the current version.   However the speed 
of mingw binary is much faster  than that of the cygwin.  Sometimes 
the slowness of cygwin octave 2.1.73 were different when version of 
cygwin1.dll were changed.  (I could not remember correctly. But the 
difference might be 30-40% for LSODE solving speed.) 

Why were the slowness depneds on the  cygwin1.dll?
Why does the sjlj-EH on the mingw not cause such slowness?

I cannot understant at this point.
Perhaps this is lack of my correct knowledge.
If you donot mind, it will be grateful fo me you to explain again 
more comrehensively for the mere user like me.

Tatsuro MATSUOKA

Tatsuro MATSUOKA 

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