BUG: nrf_delay doesn't compile using nRF52 on GCC

Question

Building nrf_delay.c (or anything else including nrf_delay.h ) with NRF52 defined produces: 
 arm-none-eabi-gcc -I C:\Nordic
RF5_SDK_11.0.0-2.alpha\components\device -D_DEBUG -DNRF52 -DDEBUG -std=gnu11 -mcpu=cortex-m0 -mthumb -mabi=aapcs -Wall -Wno-switch -ffunction-sections -fdata-sections -ggdb -c C:\Nordic
RF5_SDK_11.0.0-2.alpha\components\drivers_nrf\delay
rf_delay.c -o build
rf_delay.o
C:\Windows\ccESAXKg.s: Assembler messages:
C:\Windows\ccESAXKg.s:58: Error: instruction not supported in Thumb16 mode -- `subs r0,r0,#1'
 
 (Using GCC ARM Tools for Embedded 5_2-2015q4, nRF5 SDK 11.0.0-2.alpha.) 
 If where nrf_delay.h has 
 #ifdef NRF51
 
 I replace it with 
 #if defined(NRF51) || defined(NRF52)
 
 the problem is fixed. There are other NRF52 checks in the file (mainly to add more NOP s).

RK · Accepted Answer

it's because you're compiling for the wrong core. 
 -mcpu-cortex-m0
 
 the nRF52 you're targetting is the M4 and gas treats subs differently by default (which is arguably incorrect gas behaviour but it's long-standing incorrect gas behaviour) 
 Not that anyone should be using divided assembler syntax anyway anymore, and that's not going to, and doesn't work with, clang for instance. So I think the whole ifdef should go and the entire file should be 
 .syntax unified
 
 I don't know why it's switched only for the nrf51, possibly in an attempt to 'do no harm' when someone found the original didn't compile.