[Bug tree-optimization/106533] loop distribution not distributing inner loop (to memcpy) when perfect loop nest

[vineetg at rivosinc dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106533

--- Comment #3 from Vineet Gupta <vineetg at rivosinc dot com> ---
FWIW this was seen with riscv64 build of gcc, but same tree behavior seen with
aarch64 gcc 12.1.

For single copy-loop src, final output is inline copy loop

-->8--
  <bb 11> [local count: 1063004409]:
  # j_131 = PHI <j_92(28), 0(10)>
  # ivtmp_135 = PHI <ivtmp_88(28), 10000000(10)>
  _10 = a[j_131];
  c[j_131] = _10;
  j_92 = j_131 + 1;
  ivtmp_88 = ivtmp_135 - 1;
  if (ivtmp_88 != 0)
    goto <bb 28>; [99.00%]
  else
    goto <bb 12>; [1.00%]


.L74:
// ../stream-4-loop.c:315:          c[j] = a[j];
        ldr     q0, [x27, x0]   // MEM <vector(2) double> [(double *)&a +
ivtmp.224_247 * 1], MEM <vector(2) double> [(double *)&a + ivtmp.224_247 * 1]
        str     q0, [x19, x0]   // MEM <vector(2) double> [(double *)&a +
ivtmp.224_247 * 1], MEM <vector(2) double> [(double *)&c + ivtmp.224_247 * 1]
        add     x0, x0, 16      // ivtmp.224, ivtmp.224,
        cmp     x0, x28 // ivtmp.224, tmp291
        bne     .L74
-->8--


While for multi-loop src we see

-->8--

  MEM <unsigned char[80000000]> [(char * {ref-all})&c] = MEM <unsigned
char[80000000]> [(char * {ref-all})&a];

        bl      memcpy
-->8--