I warn anybody before using ARM Keil 4.13a. It generates defective code. I have spent several hours with debugging a code that has been already worked. The problem affects local variables of functions and passing arguments. Code has been wrongly compiled without any optimization. I have no courage and time to test optimizations.
I also encourage Keil not to publish Keil 4.13a any more.
Keil 4.12 seems to be OK.
"You are also lucky that your employer is paying hours and/or days (each of you know how much...) of your extra work to locate the bug in development tool and provide the evidence."
But, if you don't know that the problem is with the compiler, you are potentially just giving Keil support the task of finding a bug in your code. They are not paid to do that.