-O2 breaks this lib on atmel M0

[cujomalainey]

• Arduino board: itsy bitsy m0

• Arduino IDE version (found in Arduino -> About Arduino menu): platformio 6.0.2

• List the steps to reproduce the problem below (if possible attach a sketch or copy the sketch code in too):

Use the following build config and try and use the BusIO library

[env:itsy]
platform = atmelsam
board = adafruit_itsybitsy_m0
framework = arduino
build_flags = -O2
build_unflags = -Os
lib_deps = 6214

main.cpp

#include "Wire.h"
#include <Adafruit_SPIDevice.h>

void setup() {}
void loop() {}

build output (dirty build to reduce length)

Processing itsy (platform: atmelsam; board: adafruit_itsybitsy_m0; framework: arduino)
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Verbose mode can be enabled via `-v, --verbose` option
CONFIGURATION: https://docs.platformio.org/page/boards/atmelsam/adafruit_itsybitsy_m0.html
PLATFORM: Atmel SAM (7.1.0+sha.ec05bdd) > Adafruit ItsyBitsy M0
HARDWARE: SAMD21G18A 48MHz, 32KB RAM, 256KB Flash
DEBUG: Current (atmel-ice) External (atmel-ice, blackmagic, jlink)
PACKAGES:
 - framework-arduino-samd-adafruit @ 1.7.5
 - framework-cmsis @ 2.50400.181126 (5.4.0)
 - framework-cmsis-atmel @ 1.2.2
 - toolchain-gccarmnoneeabi @ 1.90301.200702 (9.3.1)
LDF: Library Dependency Finder -> https://bit.ly/configure-pio-ldf
LDF Modes: Finder ~ chain, Compatibility ~ soft
Found 12 compatible libraries
Scanning dependencies...
Dependency Graph
|-- Adafruit BusIO @ 1.12.0
|   |-- SPI @ 1.0
|   |   |-- Adafruit Zero DMA Library @ 1.1.0
|   |   |   |-- Adafruit TinyUSB Library @ 1.4.3
|   |   |-- Adafruit TinyUSB Library @ 1.4.3
|   |-- Wire @ 1.0
|   |   |-- Adafruit TinyUSB Library @ 1.4.3
|-- Wire @ 1.0
|   |-- Adafruit TinyUSB Library @ 1.4.3
Building in release mode
Compiling .pio/build/itsy/src/main.cpp.o
Archiving .pio/build/itsy/lib716/libAdafruit_ZeroDMA.a
Indexing .pio/build/itsy/lib716/libAdafruit_ZeroDMA.a
Archiving .pio/build/itsy/lib0f0/libSPI.a
Indexing .pio/build/itsy/lib0f0/libSPI.a
Compiling .pio/build/itsy/lib6bd/Wire/Wire.cpp.o
Compiling .pio/build/itsy/libc16/Adafruit BusIO/Adafruit_BusIO_Register.cpp.o
Compiling .pio/build/itsy/libc16/Adafruit BusIO/Adafruit_I2CDevice.cpp.o
Compiling .pio/build/itsy/libc16/Adafruit BusIO/Adafruit_SPIDevice.cpp.o
/var/folders/wy/yddn63455wd2vk7m62shqd780000gn/T//ccEbUdN3.s: Assembler messages:
/var/folders/wy/yddn63455wd2vk7m62shqd780000gn/T//ccEbUdN3.s:462: Error: lo register required -- `sub r10,#1'
Compiling .pio/build/itsy/FrameworkArduino/WInterrupts.c.o
Compiling .pio/build/itsy/FrameworkArduino/WMath.cpp.o
Compiling .pio/build/itsy/FrameworkArduino/WString.cpp.o
Compiling .pio/build/itsy/FrameworkArduino/abi.cpp.o
Compiling .pio/build/itsy/FrameworkArduino/avr/dtostrf.c.o
*** [.pio/build/itsy/libc16/Adafruit BusIO/Adafruit_SPIDevice.cpp.o] Error 1