为什么启用优化时 GCC 11 编译器会产生奇怪的输出

请查看以下代码:

#include <stdio.h>
#include <stdint.h>

int main()
{
    uint8_t run = 1;

    /* Define variable of interest and set to random value */
    uint32_t dwTime = 0xdeadc0de;

    /* Define uint16_t pointer */
    uint16_t* tmpU16;
    /* Assign least 16 bits from dwTime to tmpU16 by downcasting from uint32_t to uint16_t */
    tmpU16 = (uint16_t*)&dwTime;

    /* Print content of tmpU16 */
    fprintf(stderr, "TEST: %04x\n", *tmpU16); /* Will print "TEST: c0de" here */

    /* This loop will run exactly once */
    while (run)
    {
        /* Print content of tmpU16 AGAIN (content of tmpU16 should not have changed here!) */
        /* Will print "TEST: 0000" here when optimization is enabled */
        /* Will print "TEST: c0de" here when optimization is disabled */
        fprintf(stderr, "TEST: %04x\n", *tmpU16);

        /* Increment tmpU16 pointer by 1 (yes, this does not make sense but it should not do any harm
        either, unless something gets written to its address AFTER incrementing */
        tmpU16++;
        run--;
    }

    return 0;
}

当使用GCC 11编译此代码并启用优化(例如-O2)时，它将产生以下输出:

TEST: c0de
TEST: 0000

当编译此代码时，没有进行优化(-O0)，它将生成:

TEST: c0de
TEST: c0de

我假设在执行第一个fprintf之后，while循环中的下一个fprintf将立即执行.在这两个fprintf之间什么都不应该发生，因此tmpU16的内容保持不变.

然而，当我注释掉tmpU16++指针增量时，它会产生正确的优化输出.

为什么，这里发生了什么？