GCC options and floating-point correctness (benchmarks)

[Scott Robert Ladd]

Dan Nicolaescu wrote:
> Scott Robert Ladd <coyote@coyotegulch.com> writes:
> 
>   > Joseph S. Myers wrote:
>   >> What if -ffloat-store is used in alternative to those?  It doesn't
>   >> actually work as far as causing conformance (e.g., casts to same type
>   >> still get discarded rather than reducing precision), but it is supposed to
>   >> help.
>   >
>   > -ffloat-store and -mieee-fp don't change the results.
> 
> This is contradicted by my results. 

Okey-dokey, as we say here in the wild, wild west.

 From my proc/cpuingo, I get:

vendor_id       : GenuineIntel
cpu family      : 15
model           : 2
model name      : Pentium 4 (Northwood)
stepping        : 7
cpu MHz         : 2785.075
cache size      : 512 KB

The following two command lines produce the exact same result from 
paranoia (1 defect):

   gcc -o paranoiag -ffloat-store -march=pentium4 -ffast-math \
               -mfpmath=sse -lm paranoia.c

   gcc -o paranoiag -march=pentium4 -ffast-math -mfpmath=sse \
		-lm paranoia.c

In other words, -ffloat-store made no difference -- and using the either 
command above produces a better (fewer problems) result than does your:

   gcc -O2 -ffloat-store paranoia.c -lm

Note that I am running tree-ssa as my compiler; this is very different 
from gcc 3.2.

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