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If one macro is defined for "assignment": Ex. #define equal(a,b) {a=b; }
And write: equal(A,1); equal(A,2); equal(A,3);
where A is pointer to XDATA space(mapped to H/W)
Keil C will "optimize" them and final result is A=3 ? or Keil C won't do this and expand them one by one ?
Thanks in advance...
As Nevill says, the macros are expanded by the preprocessor, and the compiler "sees" only the result of the expansion.
Therefore whether the code originated from a macro expansion, or was typed verbatim, makes absolutely no differences whatsoever to the compiler.
This, in turn, means that the use of a macro (or not) makes absolutely no differences whatsoever to the optimisation behaviour.
This is all standard 'C' stuff - nothing specifically to do with Keil or the 8051.
Incidentally, what would be the point of such a macro?
Thanks for all your opinions first ! Maybe i used unsuitable example...Below is the true story and I want to explain why.
@1 I got one code base and found the following way is used to access h/w registers: #define regA *((unsigned char xdata *) 0xa1) ... regA = 0xFF; ... while(regA);
@2 I try to add code segments: regA = 0x01; regA = 0x02; regA=0x03; and I found each statement is executed and no loss...
@3 "volatile" is not used above and my entire code did not use "volatile" , but h/w access works well. Besides, XBYTE/XWORD and _at_ are NOT used... (that is, the 3 ways listed in doc: http://www.keil.com/support/docs/1455.htm are NOT used)
I can not explain the phenomenon and the only thing I can suspect is: #define creates a macro and maybe after expansion these codes are NOT optimized...
"I can not explain the phenomenon"
I explained it to you in your other thread on exactly the same subject:
http://www.keil.com/forum/docs/thread13388.asp
That's the trouble with creating duplicate threads on the same subject!
Thanks for your opinion...Initially I thought these 2 were different and thus posted 2 threads.
Please help to remove one of them if available...
Thanks anyway !
Thanks for your opinion
It is not an "opinion" =:0
They did not respond with opinions, but with facts.
Another thing - a #define named equal(a,b) should really represent a comparison - (is a equal to b?).
If you want your define to assign values, you should call it assign(a,b). Now, this was an opinion - never use confusing names for variables, defines, functions, ...
But as already mentioned, the preprocessor is really a preprocessor (even if implemented inside the compiler) doing text-based search/replace in your source code before the compiler starts to decide what the code looks like and starts with optimizations/code generation.
Thanks for all the facts you provided ^o^