Re: Filed PR jit/66812 for the code generation issue

[Dibyendu Majumdar <mobile@majumdar.org.uk>]

Apologies I think the previous description of the flow was incorrect.
Here is my second attempt (this is doing my head in so I will stop
now):

1 [2] LOADNIL   0 0

entry:
  cl = (struct ravi_LClosure *)L->ci->func->value_.gc;
  (void)raviV_op_loadnil (L->ci, (int)0, (int)0);

Above sets register 0 (local variable IX) to NIL

2 [3] LOADK     1 -1 ; 10

  (&L->ci->u.l.base[(int)1])->value_.i = (&cl->p->k[(int)0])->value_.i;
  (&L->ci->u.l.base[(int)1])->tt_ = (&cl->p->k[(int)0])->tt_;

This sets the register at 1 (temporary) to 10.

3 [3] TEST     1 1
4 [3] JMP       0 0 ; to 5

The above two bytecodes go together. This says that if register 1 is
true then do JMP else skip JMP.

So we get:

  comparison_0_5 = (&L->ci->u.l.base[(int)1])->tt_ == (int)0;
  comparison_0_6 = (&L->ci->u.l.base[(int)1])->tt_ == (int)1;
  comparison_0_7 = (&L->ci->u.l.base[(int)1])->value_.b == (int)0;
  isfalse_0_4 = comparison_0_5 || comparison_0_6 && comparison_0_7;
  if (!(isfalse_0_4)) goto OP_TEST_do_jmp_2_8; else goto OP_TEST_do_skip_2_9;

Since register 1 is true (ie. not false) we therefore jump to jmp_2_8.

OP_TEST_do_jmp_2_8:
  goto jmp_5_1;

jmp_5_1:

5 [3] LOADBOOL 1 0 0

This is setting register 1 to false so we get:

  (&L->ci->u.l.base[(int)1])->value_.b = (int)0;
  (&L->ci->u.l.base[(int)1])->tt_ = (int)1;

Next instruction is:

6 [3] TEST     1 0
7 [3] JMP       0 1 ; to 9

Now this is saying that if register 1 is false then do JMP else skip JMP.

  comparison_0_11 = (&L->ci->u.l.base[(int)1])->tt_ == (int)0;
  comparison_0_12 = (&L->ci->u.l.base[(int)1])->tt_ == (int)1;
  comparison_0_13 = (&L->ci->u.l.base[(int)1])->value_.b == (int)0;
  isfalse_0_10 = comparison_0_11 || comparison_0_12 && comparison_0_13;
  if (!(!(isfalse_0_10))) goto OP_TEST_do_jmp_5_14; else goto
OP_TEST_do_skip_5_15;

Since we know that register 1 is false as above then the code should
do the jump to jmp_5_14:

OP_TEST_do_jmp_5_14:
  goto jmp_9_2;

Next we jump to 9_2 which is the start of the return statement.

Here we essentially have a repeat of what was in entry block:

9 [3] LOADK     1 -1 ; 10
10 [3] TEST     1 1
11 [3] JMP       0 0 ; to 12

jmp_9_2:
  (&L->ci->u.l.base[(int)1])->value_.i = (&cl->p->k[(int)0])->value_.i;
  (&L->ci->u.l.base[(int)1])->tt_ = (&cl->p->k[(int)0])->tt_;
  comparison_0_17 = (&L->ci->u.l.base[(int)1])->tt_ == (int)0;
  comparison_0_18 = (&L->ci->u.l.base[(int)1])->tt_ == (int)1;
  comparison_0_19 = (&L->ci->u.l.base[(int)1])->value_.b == (int)0;
  isfalse_0_16 = comparison_0_17 || comparison_0_18 && comparison_0_19;
  if (!(isfalse_0_16)) goto OP_TEST_do_jmp_9_20; else goto OP_TEST_do_skip_9_21;

So the JMP is taken and we go to 9_20:
OP_TEST_do_jmp_9_20:
  goto jmp_12_3;

jmp_12_3:

12 [3] LOADBOOL 1 0 0

  (&L->ci->u.l.base[(int)1])->value_.b = (int)0;
  (&L->ci->u.l.base[(int)1])->tt_ = (int)1;

Above sets the register 1 to false and this is the return value.

Next the return instruction begins:

  L->top = &L->ci->u.l.base[(int)2];
  comparison_0_22 = cl->p->sizep > (int)0;
  if (comparison_0_22) goto OP_RETURN_if_sizep_gt_0_12_23; else goto
OP_RETURN_else_sizep_gt_0_12_24;