3.7 Predeclared extension register names in AArch32 state
You can write the names of Advanced SIMD and floating-point registers either in upper case or lower case.
The following table shows the predeclaredextension register names:
Table 3-3 Predeclared extension registers in AArch32 state
Advanced SIMD quadword registers
Advanced SIMD doubleword registers, floating-point double-precisionregisters
Floating-point single-precision registers
You can write the register names either in upper case or lowercase.