GCC options and floating-point correctness (benchmarks)

[Scott Robert Ladd]

Theodore Papadopoulo wrote:
> coyote@coyotegulch.com said:
> 
>>I produced the following results for a C version of PARANOIA on a
>>2.8GHz  Pentium 4 (Northwood core), HT enabled, using a very recent
>>build of the  tree-ssa branch. I'll be glad to send copies of the
>>benchmark source to  anyone who requests it privately. 
> 
> 
> Do you have those for intel's compiler ??

icc -o paranoiai -xN -tpp7 paranoia.c
icc -o paranoiai -xN -tpp7 -mp1 paranoia.c
icc -o paranoiai -xN -tpp7 -mp paranoia.c
icc -o paranoiai -xN -tpp7 -ipo paranoia.c
icc -o paranoiai -xN -tpp7 -mp1 paranoia.c
icc -o paranoiai -xN -tpp7 -mp paranoia.c
icc -o paranoiai -xN -tpp7 -O1 paranoia.c
icc -o paranoiai -xN -tpp7 -O2 paranoia.c
icc -o paranoiai -xN -tpp7 -O3 paranoia.c
icc -o paranoiai -xN -tpp7 -O1 -ipo paranoia.c
icc -o paranoiai -xN -tpp7 -O2 -ipo paranoia.c
icc -o paranoiai -xN -tpp7 -O3 -ipo paranoia.c
icc -o paranoiai -xN -tpp7 -O1 -ipo -mp1 paranoia.c
icc -o paranoiai -xN -tpp7 -O2 -ipo -mp1 paranoia.c
icc -o paranoiai -xN -tpp7 -O3 -ipo -mp1 paranoia.c
icc -o paranoiai -xN -tpp7 -O1 -ipo -mp paranoia.c
icc -o paranoiai -xN -tpp7 -O2 -ipo -mp paranoia.c
icc -o paranoiai -xN -tpp7 -O3 -ipo -mp paranoia.c

(no failures)
(no serious defects)
(no defects)
The number of  FLAWs  discovered =         1.
  - - - - - - - - - - - - - - -

Yes, I checked to see if the code changed with each combination of 
options; it did. In fact, the "flaw" is different with different options.

With -mp, the single test that failed was:

  - - - - - - - - - - - - - - -
Sticky bit used incorrectly or not at all.
FLAW:  lack(s) of guard digits or failure(s) to correctly round or chop
  - - - - - - - - - - - - - - -

Without -mp, the single flaw was:

  - - - - - - - - - - - - - - -
FLAW:  X = 3.05947655544740190e-308
         is not equal to Z = 2.22507385850720138e-308 .
yet X - Z yields 0.00000000000000000e+00 .
  - - - - - - - - - - - - - - -

Given that GCC exhibits FAILURES and DEFECTS, even under the best of 
circumstances, suggests that ICC may have a leg up when it comes to this 
benchmark.


-- 
Scott Robert Ladd
Coyote Gulch Productions (http://www.coyotegulch.com)
Software Invention for High-Performance Computing