[Bug c/30475] assert(int+100 > int) optimized away

[felix-gcc at fefe dot de]

------- Comment #25 from felix-gcc at fefe dot de  2007-01-17 19:04 -------
Well, duh.  You removed the security checks.

Hey, I have one for you, too.  Optimize away all calls to pthread_mutex_lock,
and lo and behold, multithreaded code will be much faster!  It will also be
broken, but apparently, that's not much of a concern around here.

The most time critical code I have, I just benchmarked.

  $ gcc -O3 -fomit-frame-pointer -funroll-loops -march=athlon64 -o t t.c misc.c
add.c mul.c write.c read.c comba.c
  $ ./t
  adding two bignums: 84 cycles
  multiply two bignums: 1414 cycles
  writing a bignum as radix 10: 207488 cycles
  comba: 1467 cycles
  $ gcc -O3 -fomit-frame-pointer -funroll-loops -march=athlon64 -o t t.c misc.c
add.c mul.c write.c read.c comba.c -fwrapv
  adding two bignums: 82 cycles
  multiply two bignums: 1414 cycles
  writing a bignum as radix 10: 202761 cycles
  comba: 1465 cycles
  $

So, uh, where does the optimization part about your "optimization" come in? 
This is code that has no integer overflow checks.  So my conjecture is: your
"optimization" makes code faster in exactly those cases where it removes
security checks from it, endangering people on the way.

So, again, please make -fwrapv the default, and I'll leave you alone.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30475