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Load and store multiple register instructions

The ARM and Thumb instruction sets include instructions that load and store multiple registers. These instructions can provide a more efficient way of transferring the contents of several registers to and from memory than using single register loads and stores.

Multiple register transfer instructions are most often used for block copy and for stack operations at subroutine entry and exit. The advantages of using a multiple register transfer instruction instead of a series of single data transfer instructions include:

  • Smaller code size.
  • A single instruction fetch overhead, rather than many instruction fetches.
  • On uncached ARM processors, the first word of data transferred by a load or store multiple is always a nonsequential memory cycle, but all subsequent words transferred can be sequential memory cycles. Sequential memory cycles are faster in most systems.

The lowest numbered register is transferred to or from the lowest memory address accessed, and the highest numbered register to or from the highest address accessed. The order of the registers in the register list in the instructions makes no difference.

You can use the --diag_warning 1206 assembler command line option to check that registers in register lists are specified in increasing order.