A problem about loop store motion

["Jiangning Liu" <jiangning dot liu at arm dot com>]

Hi,

For this small test case,

int *l, *r;
int test_func(void)
{
	int i;
	int direction;
	static int pos;

	pos = 0;
	direction = 1;

	for ( i = 0; i <= 400; i++ )
	{
		if ( direction == 0 )
			pos = l[pos];
		else
			pos = r[pos];

		if ( pos == -1 )
		{
			pos = 0;
			direction = !direction;
		}
	}
	return i;
}

In middle end, I don't see pos is sunk out of loop by loop store motion. Any
idea?

The dump after lim is like below, and I expect a SSA symbole xxx_lsm could
be created with this pass.

;; Function test_func (test_func, funcdef_no=0, decl_uid=4057, cgraph_uid=0)


Symbols to be put in SSA form
{ .MEM }
Incremental SSA update started at block: 0
Number of blocks in CFG: 12
Number of blocks to update: 11 ( 92%)


test_func ()
{
  int pretmp.14;
  unsigned int pretmp.13;
  int prephitmp.12;
  int pretmp.11;
  unsigned int pretmp.10;
  int pretmp.9;
  int D.4088;
  static int pos;
  int direction;
  int i;
  _Bool D.4082;
  int pos.5;
  int * D.4078;
  int * r.4;
  int pos.3;
  int * D.4074;
  unsigned int D.4073;
  unsigned int pos.2;
  int pos.1;
  int * l.0;

<bb 2>:
  pos = 0;
  l.0_6 = l;
  r.4_12 = r;

<bb 3>:
  # i_32 = PHI <i_21(11), 0(2)>
  # direction_37 = PHI <direction_2(11), 1(2)>
  # prephitmp.12_35 = PHI <pretmp.11_1(11), 0(2)>
  if (direction_37 == 0)
    goto <bb 4>;
  else
    goto <bb 5>;

<bb 4>:
  pos.1_7 = prephitmp.12_35;
  pos.2_8 = (unsigned int) pos.1_7;
  D.4073_9 = pos.2_8 * 4;
  D.4074_10 = l.0_6 + D.4073_9;
  pos.3_11 = *D.4074_10;
  pos = pos.3_11;
  goto <bb 6>;

<bb 5>:
  pos.1_13 = prephitmp.12_35;
  pos.2_14 = (unsigned int) pos.1_13;
  D.4073_15 = pos.2_14 * 4;
  D.4078_16 = r.4_12 + D.4073_15;
  pos.5_17 = *D.4078_16;
  pos = pos.5_17;

<bb 6>:
  # prephitmp.12_31 = PHI <pos.3_11(4), pos.5_17(5)>
  pos.1_18 = prephitmp.12_31;
  if (pos.1_18 == -1)
    goto <bb 7>;
  else
    goto <bb 10>;

<bb 10>:
  goto <bb 8>;

<bb 7>:
  pos = 0;
  D.4088_36 = direction_37 ^ 1;
  direction_20 = D.4088_36 & 1;

<bb 8>:
  # direction_2 = PHI <direction_37(10), direction_20(7)>
  i_21 = i_32 + 1;
  if (i_21 != 401)
    goto <bb 11>;
  else
    goto <bb 9>;

<bb 11>:
  pretmp.11_1 = pos;
  goto <bb 3>;

<bb 9>:
  return 401;

}

Thanks,
-Jiangning