[fpc-devel] Const optimization is a serious bug

[Martin]

On 07/07/2011 16:27, Alexander Klenin wrote:
>
> 1) That the code you posted would work quite correctly if "const
> string" is fixed,
>    including all the optimizations you are suggesting in the rest of
> your message.

No.

As I said: IF the result of constant expressions like "s[a] = '<'" are 
cached (in future) depending on optimization level, then it breaks.

The 2nd evaluation, of this expression without optimization returns a 
different result from the 1st evaluation. (It may be that the example 
would need updating, but there is code where this can happen, including 
if ref-counting was done)

So depending on the 2nd evaluation being done, or cached (future 
optimization) the program flow differs.

Code which behaves unpredictable is broken.
In this case the none predictability comes from the fact that the code 
relies on a randomly observed and undocumented behaviour of todays fpc 
implementation. (the fact that today no such optimization is done)