[Tutor] Re: Why x+=y instead of x=x+y?

[lumbricus@gmx.net]

> > > > I think it is also related to the complexity of the compiler.  I
> > > > expect that any modern compiler will turn "x+=1" into INC X.  
> > > 
> > > If optimisation is turned off I sincerely hope it doesn't!
> > 
> > Why not?
> 
> Because if I'm writing a time critical program and I have 
> a loop that's running just slightly too fast with an x++ 
> in it I expect to be able to slow the loop down by changing 
> x++ to x+=1

I cant get any of my compilers (Digital UNIX Compiler Driver 3.11
and gcc) to compile (with -O0 to turn off all optimization)
 i=i+1, i+=i and i++ differently.
One (on x86) always codes "incl " the other one
(on alpha) always says "addl $1, 1, $1".
 
> If the compiler treats those two as equivalent then the 

But they _are_ equivalent IIRC. 
But I don't have a copy of the
Standard at hand to look it up *wink*.

> loop won't change. That's the kind of premature optimisation 
> that I don't want. (It also affects debugging of complex 
> code too, if the assembler is the same for x++ and x+=1 
> I'm going to have some strange results when running the 
> assembler debugger.)

Now I am really courious what compilers You use.
 
> Alan g.

Greetings, J"o!

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