Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

Andrew Pinski <pinskia@physics.uc.edu> writes:

| > 
| > | > If the above is the only without Autoconf change, I would highly
| > | > recommend Autoconf change if GCC optimizers highly value benchmarks
| > | > over running real world code.
| > | 
| > | Which one, mine or Paul's?
| > 
| > If what you propose is the only way out, and there is no way to make
| > GCC optimizers reasonable, then I believe Paul's proposal is the next
| > option. 
| 
| But that still does not address the issue is that this is not just about
| GCC any more since autoconf can be used many different compilers and is right
| now.

The Autoconf change, as I see it, is to active switches when enough
recent version of GCC is detected as I understand it is the primary
compiler at issue.

|  So if you change autoconf to default to -fwrapv and someone comes alongs
| and tries to use it with say ACC (some made up compiler right now).  The loop
| goes into an infinite loop because they treat (like GCC did) signed type overflow
| as undefined, autoconf still becomes an issue.
| 
| If you want to make the code more readable and maintainable, you can use macros like:

CPP hackery seldom repairs a fundamentally problematic construct.

| 
| MAX_USING_TYPE(type, othertype, max) \
| { \
|  ... \
|  max = (othertype) _real_max; \
| }
| 
| 
| MAX_TYPE(type, max) \
| { \
|   if (sizeof(type)==sizeof(unsigned int))\
|     MAX_USING_TYPE(unsigned int, type, max);
|   else if (..... \
|   else \
|     {
|       printf("Need another integeral type sized, %d\n", sizeof(type)); \
|       abort (); \
|     } \
| }
| 
| 
| Yes people think macros can be less reabable, but this one case actually makes
| it readable.

I dispute it is readable.  More fundamentally, I don't see how that
magically becomes more portable, and maintainable.  The set of
built-in integer types is NOT given by a closed list.  I posit that
any solution based on sizeof hackery is fundamentally non-portable and
broken. 

-- Gaby