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Imaginary losses

Imaginary losses

Posted Mar 27, 2008 21:04 UTC (Thu) by wahern (subscriber, #37304)
In reply to: Imaginary losses by wahern
Parent article: Striking gold in binutils

I forgot to test multiple calls in the same try{} block. Indeed, for every additional
back-to-back call C needs an additional two instructions (test+jump). So, for moderately long
functions, w/ a single try{} block and lots of calls to some small set of functions, I can see
C++ being faster. The trick is that you don't want the fixed-costs to exceed the gains, of
course. In the above example, C++ pulls ahead at the 4th call to noargs().

It would be an interesting exercise to count the number of function definitions, and functions
call in my code, and multiple by the respective differences of C and C++. But, it seems
complicated by the treatment of blocks in C++. I can see how in some tests C++ came out 15%
ahead, though.

In any event, there is indeed a fixed-cost to C++ exceptions. There might not be a prologue,
but the epilogue is invariably longer for functions, and, apparently, some blocks.


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