Math optimization defaults

[RainerMtb]

The API registry says at 5.8.6.3. Optimization Options that

These options are not turned on by default since it can result in incorrect output...

Specifically referring to fmad optimization I found this is not entirely true since there also is 6.15.2.1. Floating-point macros and pragmas in the C registry.

I found that on many hardware FP_CONTRACT is on by default, which enables fmadby default even without the compiler option -cl-mad-enable beeing set. This may be clarified.

[bashbaug]

I've moved this issue from OpenCL-Registry to OpenCL-Docs. It should get more attention here.