if statement containing a for loop, wont this be quite slow?

[hughperkins]

Hi,

In sger kernel, we have:

if( row + float4size < numrows ) {
   // use vector maths
} else {
   for( i = row; i < numrows; i++ ) {
      // use scalar maths
   }
}

Per my understanding:

• this will execute both branches of the 'if' systematically?
• And in the second branch, for some threads, it will loop over the entire matrix, every row in the matrix?
• and therefore, since all threads in the warp must be in lock-step, actually every thread in the entire warp will iterate over every row in the entire matrix?

[hughperkins]

Ok I played with this by commenting out these various ifs and stuff, and speed was the same.

=>closing for now.