IR program failed to compile with "-O0" "-S" options

[stkeke]

tony@Win11Z790I:~/ir/tests/debug$ cat ./dce_001.ir
{
        uintptr_t c_1 = 0;
        bool c_2 = 0;
        bool c_3 = 1;
        int32_t c_4 = 10;
        int32_t c_5 = 2;
        int32_t c_6 = 1;
        int32_t c_7 = 0;
        l_1 = START(l_14);
        int32_t d_2 = PARAM(l_1, "x", 0);
        l_3 = END(l_1);
        l_4 = LOOP_BEGIN(l_3, l_12);
        int32_t d_5 = PHI(l_4, c_7, d_7);
        int32_t d_6 = ADD(d_2, c_6);
        int32_t d_7 = ADD(d_6, d_5);
        int32_t d_8 = MUL(d_7, c_5);
        int32_t xxx = DIV(d_8, c_4);
        bool d_9 = LT(d_7, c_4);
        l_10 = IF(l_4, d_9);
        l_11 = IF_TRUE(l_10);
        l_12 = LOOP_END(l_11);
        l_13 = IF_FALSE(l_10);
        l_14 = RETURN(l_13, d_8);
}

# failed with -O0 option
tony@Win11Z790I:~/ir/tests/debug$ ~/ir/ir -O0 ./dce_001.ir -S
ir: ./ir_x86.dasc:3173: ir_emit_mul_div_mod: Assertion `def_reg != -1' failed.
Aborted

# succeeded with -O2 option
tony@Win11Z790I:~/ir/tests/debug$ ~/ir/ir -O2 ./dce_001.ir -S
test:
        leal 1(%rdi), %eax
        xorl %ecx, %ecx
.L1:
        addl %eax, %ecx
        cmpl $0xa, %ecx
        jl .L1
        leal (%rcx, %rcx), %eax
        retq

[dstogov]

I suppose, something is wrong (may be recently broken) in -O0 register allocator.
I'm going to completely rewrite it, but this is not a top priority task.