[Bug tree-optimization/95685] New: Loop invariants can't be moved out of the loop

[bina2374 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95685

            Bug ID: 95685
           Summary: Loop invariants can't be moved out of the loop
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bina2374 at gmail dot com
                CC: kito at gcc dot gnu.org, wilson at gcc dot gnu.org
  Target Milestone: ---
            Target: riscv32-unknown-elf

Command line: bin/riscv64-unknown-elf-gcc -march=rv32imafc -mabi=ilp32f -O2
-funroll-loops bar.c -S

==========
 C Source
==========
unsigned short bar(unsigned char data, unsigned short crc) {
  unsigned char i = 0;

  for (i = 0; i < 3; i++) {
    data >>= 1;
    if ((data & 1) == 1)
      crc ^= 0x2001;
  }
  return crc;
}

=========
 GCC asm
=========
bar:
        srli    a4,a0,1
        andi    t0,a4,1
        mv      a5,a0
        mv      a0,a1
        beq     t0,zero,.L2
        li      t1,8192     #
        addi    t2,t1,1     # 0x2001
        xor     a0,a1,t2
.L2:
        srli    a1,a5,2
        andi    a2,a1,1
        beq     a2,zero,.L3
        li      a3,8192     #
        addi    a6,a3,1     # 0x2001
        xor     a0,a0,a6
.L3:
        srli    a7,a5,3
        andi    t3,a7,1
        beq     t3,zero,.L4
        li      t4,8192     #
        addi    t5,t4,1     # 0x2001
        xor     a0,a0,t5
.L4:
        ret

If I compile it without -funroll-loops, loop invariant code motion works:
bar:
        li      a2,8192     #
        mv      a4,a0
        li      a5,3
        mv      a0,a1
        addi    a2,a2,1     # 0x2001
.L3:
        srli    a4,a4,1
        addi    a5,a5,-1
        andi    a3,a4,1
        andi    a5,a5,0xff
        beq     a3,zero,.L2
        xor     a0,a0,a2
.L2:
        bne     a5,zero,.L3
        ret

I guess the problem is the order of optimization passes.
Because cunroll pass makes the loop no longer a loop, loop2_invariant can't
work on it.

=======================
 Ideal Code Generation 
=======================
bar:
        srli    a4,a0,1
        andi    t0,a4,1
        mv      a5,a0
        mv      a0,a1
        li      t1,8192     #
        addi    t2,t1,1     # t2 = 0x2001
        beq     t0,zero,.L2
        xor     a0,a1,t2
.L2:
        srli    a1,a5,2
        andi    a2,a1,1
        beq     a2,zero,.L3
        xor     a0,a0,t2    # Use t2
.L3:
        srli    a7,a5,3
        andi    t3,a7,1
        beq     t3,zero,.L4
        xor     a0,a0,t2    # Use t2
.L4:
        ret