Lpc2000

At 01:35 AM 4/10/2006 +0000, jayasooriah wrote:
>--- In lpc2000@yahoogroups.com, Robert Adsett <subscriptions@...> wrote:
> > I do see uses for assembler, I am just of the opinion, informed
> > by my experiences, that inline assembler causes more problems
> > than it fixes.
>
>My experience tells me otherwise.  Inline assembler has its place just
>like any other feature *provided* one understands how to use it before
>one does.

Apparently we have experienced different projects and tools.

I have never used a compiler seriously and not had it break at some point 
on me.  The only exception so far is GCC.  The most common point of 
failure, by far, are the architecture specific extensions.  Interrupt 
keywords, inline assembly, memory placement modifiers etc...  Curiously, 
the second most common failure point seems to be switch statements.

>If you can give us some examples of where it has caused more problems
>than it fixed, I might be able to explain what I think went wrong.

Problem 1:  Nearly all implementations suffer from a lack of 
documentation.  One case in particular I remember the documentation boiling 
down to more or less "the inline asm syntax is  asm assembly 
instruction;"  Needless to say, I didn't even attempt that one.

Problem 2: Incompatible C syntax The form above is obviously not 
compatible, so is the form
         #asm
                 assembly instructions
         #endasm
They both cause problems with tools and reuse.  Tools are generally the 
bigger issue.

Problem 3: optimization. If the assembly is just inserted in the middle of 
the generated code before being passed to the backend it is sometimes 
optimized away.

Problem 4: Register reappropriation.  Not a good term but it will do.  The 
compiler documents the calling convention but when using inline even at the 
beginning of the function the compiler appropriates the register for other 
temporary uses first so you can never be sure that you will get what you 
were expecting when you originally wrote it.

That being said I have run across compilers that only allowed inline (they 
had no separate assembler)  In both cases though the compilers resembled C 
in much the same way Java  does so the solution in both cases was really to 
get a proper tool chain.


I have used multiple compilers on multiple architectures and experience has 
taught me to approach architecture specific extensions with caution and if 
their are clear simple alternatives as there are for interrupts and 
assembler avoid them all together.    I'd rather not spend my time 
debugging the compiler if I can avoid it.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
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