Here's a question to ask: does it matter? Here you are with a product to ship, a customer base, a deadline, and some really obscure bug that appears only in the release version! Why optimize at all? Does it really matter? If it doesn't, why are you wasting your time? Just turn off optimizations in the release version and recompile. Done. No fuss, no muss. A bit larger, a bit slower, but does it matter? Read my essay about optimization being your worst enemy.
Optimize only what counts
Generally, GUI code needs little or no optimization, for the reasons given in my essay. But as I point out in that essay, the inner loops really, really matter. Sometimes you can even selectively enable optimizations in the inner loop that you wouldn't dare enable globally in your program, such as telling a certain routine that no aliasing is possible. To do this, you can apply optimization pragmas around the routine.
For example, look in the compiler help under "pragmas", and the subtopic "affecting optimization". You will find a set of pointers into detailed discussions.
inline functions
You can cause any function to be expanded inline if the compiler judges this to have a suitable payoff. Just add the attribute inline to a function declaration. For C/C++, this requires that the function body be defined in the header file, e.g.,
class whatever {
public:
inline getPointer() { return p; }
protected:
something * p;
}
A function will normally not be compiled inline unless the compiler has been asked to compile inline functions inline, and it has decided it is OK to do so. Go read the discussion in the manual. The compiler switches which enable optimization of inline expansion are set from the Project | Settings, select the C/C++ tab, select the Optimizations category, and select the type of optimization under the Inline function expansion dropdown. Usually doing /Ob1 is sufficient for a release version. Note that if your bug comes back, you've got a really good idea where to look.
intrinsic functions
The compiler knows that certain functions can be directly expanded as code. Functions that are implicitly inlineable include the following
_lrotl, _lrotr, _rotl, _rotr, _strset, abs, fabs, labs, memcmp, memcpy, memset, strcat, strcmp, strcpy, and strlen
Note that there is very little advantage to implicitly expanding one of these to code unless it is already in a time-critical part of the program. Remember the essay: measure, measure, measure.
An intrinsic function often makes the code size larger, although the code is faster. If you need it, you can simply declare
#pragma intrinsic(strcmp)
and all invocations of strcmp which follow will be expanded as inline code. You can also use the /Oi compiler switch, which is set by Project | Settings, C/C++ tab, category Optimizations, and if you select Custom, select Generate Intrinsic Functions. You will probably never see a bug which occurs in optimized code because of intrinsic expansions.
Note that coding strcmp as a function call in your code can be a seriously losing idea anyway, if you ever think you might build a Unicode version of your app. You should be writing _tcscmp, which expands to strcmp in ANSI (8-bit character) applications and _wcscmp in Unicode (16-bit character) applications.
Really Tight Control
If you have a high-performance inner loop, you may want to tell the compiler that everything is safe. First, apply any const or volatile modifiers that would be necessary. Then turn on individual optimizations, such as
#pragma optimize("aw", on)
This tells the compiler that it can make a lot of deep assumptions about aliasing not being present. The result will be much faster, much tighter code. Do NOT tell the compiler, globally, to assume no aliasing! You are very likely to do yourself in because you have systematically violated this limitation all over the place (it is easy to do, and hard to find if you've done it). That's why you only want to do this sort of optimization in very restricted contexts, where you know you have total control over what is going on.
When I have to do this, I usually move the function to a file of its own, and only the function I want to optimize can therefore be affected.
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