[Bug tree-optimization/92649] New: dead store elimination

[jiangning.liu at amperecomputing dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92649

            Bug ID: 92649
           Summary: dead store elimination
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jiangning.liu at amperecomputing dot com
  Target Milestone: ---

For this small case,

int f(void)
{
        int i, a[1024];

        for (i=0; i<1024; i++)
                a[i] = 5;
        return a[0];
}

"gcc -O3" can't figure out the memory stores from a[1] to a[1023] all can be
eliminated. The assembly code for aarch64 is as below.

        movi    v0.4s, 0x5
        sub     sp, sp, #4096
        mov     x0, sp
        add     x1, sp, 4096
.L2:
        str     q0, [x0], 16
        cmp     x0, x1
        bne     .L2
        ldr     w0, [sp]
        add     sp, sp, 4096
        ret