IMPROVED ARM INTERRUPT HANDLING

[protobits]

  Description: The ARM and Cortex-M3 interrupt handlers restores all registers
               upon return. This could be improved as well:  If there is no
               context switch, then the static registers need not be restored
               because they will not be modified by the called C code.
               (see arch/renesas/src/sh1/sh1_vector.S for example)
  Status:      Open
  Priority:    Low