TITLE: runtime cost of exceptions

(Newsgroups: comp.lang.c++.moderated)


PROBLEM: pcm@scammell.ecos.tne.oz.au (Peter Murray)

[...]
(How does exception handling affect size/performance?)


RESPONSE: rmartin@oma.com (Robert C. Martin), 11 Apr 96

I recently did a timing analysis of BC4.51 running on a 486-33 laptop.

	Exceptions on		Exceptions off

lt	.329us			0.34us
nv	1.001us			0.954us
voh	0.136us (13.58%)	0.137us (13.9%)
snvcd	3.593us			2.142us
svcdoh	0.324us (9.02%)		0.331us (15.5%)
hnvcd	5.1us			2.472us
hvcdoh	3.53us (69.2%)		1.269us (51.3%)
====================================================


lt      The time for a single interation of an empty for loop.  This was
        done to calibrate the model.  all the other timings were taken
        from 1e7 such loops. 

		for (long i=0; i<10000000; i++);

The next two metrics come from the following class:

	class F
	{
	  public:
	   void nv();
	   virtual void v();
	};

	void F::nv() {}
	void F::v() {}

	F f;
	F& fr=f;

nv	The time for calling a non-virtual function through a
        reference to an object.  The function had no arguments and no
        body.    i.e. time for a call to f.nv();

voh     Virtual Overhead.  The extra time required for calling a virtual
        function through a reference to an object.  i.e. this is the
        time for f.v(); minus the time for f.nv();

snvcd   Time to create and destroy on the stack an object with no
        virtual functions.  i.e. the time for:
             {O o;}  where O is a class with no virtual functions and
                     no data elements.

svcdoh  Virtual overhead.  The extra time, above and beyond snvcd, to 
        create and destroy an object on the stack; where the object
        has a virtual destructor and no data elements.

hnvcd	Time to create and destroy on a degenerate heap, an object
        with no virtual functions or data elements.  i.e. time for:
             {delete new O;} where operator new and operator delete
                             have been overridden to do nothing.

hvcdoh  Virtual overhad.  The extra time, above and beyond hnvcd to
        create and destroy, on the heap, an object with a virtual
        destructor and no data elements.