Comment 2 for bug 1812887

Okay , I've played a bit more .

I'm now using gcc 8 in my full case I still get the output I posted, but it turns out the critical line which I had simplified was

  uint8_t data = gpio & 0x3FC>>2;

My current test case :

#include <stdint.h>
static uint8_t * ram;
static uint8_t * Memory;
static unsigned int ram_addr;

void test(unsigned int gpio)
{
   uint8_t data = gpio & 0x3FC>>2;
   ram[ram_addr] = data;
   Memory[3] = data;
}

void main()
{
   ram_addr= 3;
   Memory = (uint8_t *) 0x8000000;
   ram = (uint8_t *) 0x9000000;

   test(0x7745);
   ram_addr= 4;
   test(0x7712);
   while(1);
}

void _exit(unsigned int fred)
{
   while(1);
}

gives :

00008230 <test>:
    8230: e59f3010 ldr r3, [pc, #16] ; 8248 <test+0x18>
    8234: e6ef0070 uxtb r0, r0
    8238: e893000e ldm r3, {r1, r2, r3}
    823c: e7c10002 strb r0, [r1, r2]
    8240: e5c30003 strb r0, [r3, #3]
    8244: e12fff1e bx lr
    8248: 00018af0 .word 0x00018af0