On 02/01/2016 12:55 PM, Jose Miguel Reynolds Barredo wrote:
Hi everyone, I was developing a tridiagonal block solver and I found a performance issue that is ingriguing me: doing operations with numbers in the denormalized range is around ten times slower than regular numbers (https://en.wikipedia.org/wiki/Denormal_number). As an example, I builded a very simple code:
The reason operations with denormal numbers are ten times slower has - unfortunately, as otherwise we could do something about it - nothing to do with the compiler or the run time library (of *any* language).
Denormal number operations are handled by the operating system, because it is too costly to allocate silicon to handle them on the CPU. So when the CPU detects a denormal number, it traps. This trap is caught by the OS, which dispatches the computation to a routine written for the purpose. The trap and the software implementation of the handling of the operation involving a denormal are costly, as you observed.
There is nothing the compiler writers (*any* compiler writers, not just GCC's) can do about this.
Kind regards, -- Toon Moene - e-mail: toon@xxxxxxxxx - phone: +31 346 214290 Saturnushof 14, 3738 XG Maartensdijk, The Netherlands At home: http://moene.org/~toon/; weather: http://moene.org/~hirlam/ Progress of GNU Fortran: http://gcc.gnu.org/wiki/GFortran#news
