MSVC08 & code optimizing

[deepzero]

hi,

i am writing a function in c++ (msvc2008 pro), which has to be "portable" (ie. no calls to other functions or APIs) and fast.

At one point i am using something like

    while(tlen++ < total)
        *str++ = leChar;

which works fine, but msvc choses to "optimize" it to a crt-memset call. :/

I generally noticed msvc is very keen on replacing code with crt calls to memset, even my custom memset-function, which uses an inlined REPMOV (and serves the sole purpose of making me independant from the crt...).

Is there anyway i can turn off this specific optimization feature?

I tried all sorts of linker switches; none of which worked properly.

[Aguila]

look here:
/>http://www.benshoof.org/blog/minicrt/

you can further optimize the minicrt code with inline assembly and stuff....

[deepzero]

thanks, i am aware of minicrt, using it in quiet some projects.

However, in this case i make extensive use of advanced crt features, so that`s not an option. I also doubt it would solve the problem...?

anyways, the easiest solution is

while(tlen++ < total)
{
  _asm{NOP}
  *str++ = leChar;
}

which effectively prevents the memset optimization.

I still dont see how memset is an optimization, though.

It takes more space and is slower.

Edited February 19, 2012 by deepzero

[metr0]

I had some kind of workaround back then. Something like outsourcing the code in question (in your case the loop) into a __forceinline function with #pragma optimize("", off) and on around it, respectively.