[Bug target/122140] New: bpf: wrong code for __builtin_memmove

[kristerw at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122140

            Bug ID: 122140
           Summary: bpf: wrong code for __builtin_memmove
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
            Blocks: 118443
  Target Milestone: ---
            Target: bpf-unknown-none

The following function is miscompiled at -O1 and higher optimization levels:

char a[32];
void foo (void)
{
  __builtin_memmove (a+1, a, 4);
}

The generated code is:

  foo:
        lddw    %r0,a+1
        lddw    %r1,a
        jge     %r1,%r0,.L2
        ldxb    %r2,[%r1+4]
        stxb    [%r0+4],%r2
        ldxb    %r3,[%r1+3]
        stxb    [%r0+3],%r3
        ldxb    %r4,[%r1+2]
        stxb    [%r0+2],%r4
        ldxb    %r5,[%r1+1]
        stxb    [%r0+1],%r5
        exit
  .L2:
        ldxb    %r9,[%r1+0]
        stxb    [%r0+0],%r9
        stxb    [%r0+1],%r9
        stxb    [%r0+2],%r9
        stxb    [%r0+3],%r9
        exit

wich performs an operation equivalent to: __builtin_memmove (a+2, a+1, 4).


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118443
[Bug 118443] [Meta bug] Bugs triggered by and blocking more smtgcc testing