[Bug c/90027] New: misalign variable access by piece load/store even when define STRICT_ALIGNMENT nonzero

[zhongyunde at huawei dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90027

            Bug ID: 90027
           Summary: misalign variable access by piece load/store even when
                    define STRICT_ALIGNMENT nonzero
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhongyunde at huawei dot com
  Target Milestone: ---

base gcc 7.3.0, in function expand_expr_real_1 we can see the follow code:      
 else if (SLOW_UNALIGNED_ACCESS (mode, align))
              temp = extract_bit_field (temp, GET_MODE_BITSIZE (mode),
                                        0, TYPE_UNSIGNED (TREE_TYPE (exp)),
                                        (modifier == EXPAND_STACK_PARM
                                         ? NULL_RTX : target),
                                        mode, mode, false);

it means even when we define STRICT_ALIGNMENT 1, it may still extract the store
insns with narrow alignment.
In Gcc internal, it say that SLOW_UNALIGNED_ACCESS should produce a nonzero
value when STRICT_ALIGNMENT is nonzero.

A test cases:
int foo ()
{
   volatile int *pswData = 2;  /* point to address 2 is not aligned with 4
bytes.  */
   return *pswData - *pswData;
}