Big differences on SpecFP results for gcc and icc

[Scott Robert Ladd]

Menezes, Evandro wrote:
> Each HPC application tends to be unlike others, making it difficult
> to optimize GCC for an elusive typical FP application.  Not that
> there isn't room for improvement though.

The performance of almost any HPC application can be isolated to
specific key loops, and every critical loop has different optimization
characteristics -- what improves performance on algorithm A may degrade
performance on algorithm B. See my Acovea work for many supporting examples.

My conclusion is the composite switches like -O2 are good only for
general-purpose code. Anyone explicitly interested in squeezing out the
most performance needs to do analysis and use application-specific switches.

..Scott