PTX Registers
In CUDA, PTX registers are more like symbolic virtual locations than hardware registers in the classic sense. At any given point during the execution of CUDA device code, a variable that has been assigned to a PTX register may live in one of three places:
• A hardware (SAS) register
• Local storage
• Nowhere (its value is dead)
Variables that are assigned to PTX registers are qualified with the "@register" type storage qualifier, and their locations are PTX register names. The name of a PTX register can be anything, but the compiler usually assigns a name in one of the following formats: %rN, %rdN, or %fN, where N is a decimal number.
Using compiler-generated location information, TotalView maps a PTX register name to the SASS hardware register or local memory address where the PTX register is currently allocated. If the PTX register value is "live", then TotalView shows you the SASS hardware register name or local memory address. If the PTX register value is "dead", then TotalView displays
Bad address and the PTX register name as show in
Figure 267.
