when I build a union include float16_t and uint16 with aarch64-linux-gnu-gcc-6.2.0,I will get a random value at "-O2",but a unique value at "-O0".
case:
#include "arm_neon.h"
#include <stdio.h>
typedef union {
float16_t m1;
unsigned short m2;
}MYUNION;
int main(void)
{
MYUNION U1;
U1.m1 = 5;
printf("m2 = 0x%x \n",U1.m2);
return 0;
}
aarch64-linux-gnu-gcc test.c -S -O2
1 .arch armv8-a
2 .file "test.c"
3 .section .text.startup,"ax",@progbits
4 .align 2
5 .p2align 3,,7
6 .global main
7 .type main, %function
8 main:
9 stp x29, x30, [sp, -16]!
10 adrp x0, .LC0
11 add x0, x0, :lo12:.LC0
12 mov w1, 61573
13 add x29, sp, 0
14 bl printf
15 mov w0, 0
16 ldp x29, x30, [sp], 16
17 ret
18 .size main, .-main
19 .section .rodata.str1.8,"aMS",@progbits,1
20 .align 3
21 .LC0:
22 .string "m2 = 0x%x \n"
23 .ident "GCC: (GNU) 6.2.0"
24 .section .note.GNU-stack,"",@progbits
the "61573" is a random value,why?
btw:If I use "-O0" option, I will get a unique value .
