ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Deprecated and Obsolete Features
D.5 Use of the SP as a general-purpose register
In the Thumb instruction set, you can only use the SP (R13) in a restricted set of instructions. This set covers
all the legitimate uses of the SP as a stack pointer. An attempt to encode any other instruction with SP in
place of a legitimate register results in either UNPREDICTABLE behavior, or a different instruction.
In addition, the use of SP (R13) as Rm in the high register forms of the 16-bit CMP and ADD instructions is
deprecated. Also, some forms of MOV (register) that use SP are deprecated, see MOV (register) on
page A8-196.
Most ARM instructions, unlike Thumb instructions, provide exactly the same access to the SP as to R0-R12.
This means that it is possible to use the SP as a general-purpose register. However, the use of the SP in an
ARM instruction, in any way that is not possible in the corresponding Thumb instruction, is deprecated.
See ARM instructions where SP use is not deprecated for a list of instructions that you can use for SP
manipulation.
D.5.1 ARM instructions where SP use is not deprecated
The use of the SP is deprecated in any ARM instruction that is not specified in this section.
Some uses of the SP are not deprecated in the following ARM data-processing instructions:
ADD (SP plus immediate) on page A8-28
ADD (SP plus register) on page A8-30
CMN (immediate) on page A8-74
CMN (register) on page A8-76
CMP (immediate) on page A8-80
CMP (register) on page A8-82
MOV (register) on page A8-196
SUB (SP minus immediate) on page A8-426
SUB (SP minus register) on page A8-428.
In these ARM instructions, the uses of the SP that are not deprecated are the same as those uses listed in
32-bit Thumb instruction support for R13 on page A6-4.
The use of the SP as the base register in load/store/preload instructions is not deprecated. In addition, the
use of the SP as destination or source register is not deprecated in the following instructions:
LDR (immediate, ARM) on page A8-120
LDR (literal) on page A8-122
LDR (register) on page A8-124
STR (immediate, ARM) on page A8-384
STR (register) on page A8-386.
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