Re: [RFC] Have assert macros

[Mark Mitchell <mark at codesourcery dot com>]

Nathan Sidwell wrote:

> Hi,
> I did some measurements to determine how much leaving in our self 
> checking
> mechanism of the form
>     if (expr)
>       abort()
> was costing us in compilation speed.  I built 4 --disable-checking
> compilers, with the following tweaks
> 0) baseline
> 1) #define abort to no-op, thus allowing the optimizer can remove the
> controlling expression
> 2) #define abort to no-op and g++'s my_friendly_assert to no-op
> 3) Leave abort alone, but #define my_friendly_assert to
>    __builtin_constant_p (expr) && !expr ? abort() :  0
>   thus removing the runtime-checked asserts but leaving in the compile
> time checked asserts.
>
> The results I got for cc1plus on an i686-pc-linux-gnu system were (for 
> the
> two sets of flags)
>     -g -O0      -g -O2          textsize
> #0   2.75      2.81            4,582,627
> #1   2.79(+1.5%)  2.77(-1.5%)    4,488,595(-2.0%)
> #2   2.74(-0.5%)  2.79(-0.8%)    4,468,467(-2.5%)
> #3   2.71(-1.5%)  2.74(-2.5%)    4,565,603(-0.5%)
>
> As you can see, all but unoptimzed #1 is an improvement. Why is that one
> worse?  One thing noticable about #1 is that I had many 'foo might be 
> used
> uninitialized' warnings during bootstrap.  These all come from code like
...

> Opinions on this proposal?

I am in favor.  I think that you should wait a few days, and then 
interpret silence as assent, if nobody else speaks up...

--
Mark Mitchell
CodeSourcery, LLC
(916) 791-8304
mark@codesourcery.com