gh-145866: Implement POP_ITER as macro op using POP_TOP

[brijkapadia]

As the JIT can optimize _POP_TOP uops, I implemented POP_TOP for the POP_ITER instruction. I am fairly confident that this is the right solution but I am new to the JIT and would welcome any feedback.

• Issue: Convert more uops to leave their inputs on the stack to be cleaned up by _POP_TOP #145866

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[brijkapadia]

Okay, I reopened as I found a case where POP_ITER makes it to a tier 2 trace.

Here is one case:

for _ in range(5000):
    for _ in range(5):
        pass

PYTHON_LLTRACE=2 gave this output:

Trace info

   1 ADD_TO_TRACE: _START_EXECUTOR (0, target=27, operand0=0x7f098c758146, operand1=0)
   2 ADD_TO_TRACE: _MAKE_WARM (0, target=0, operand0=0, operand1=0)
0x7f098c758040 27: POP_ITER(0) 0
   3 ADD_TO_TRACE: _CHECK_VALIDITY (0, target=27, operand0=0, operand1=0)
   4 ADD_TO_TRACE: _SET_IP (0, target=27, operand0=0x7f098c758146, operand1=0)
   5 ADD_TO_TRACE: _POP_TOP_NOP (0, target=27, operand0=0, operand1=0)
   6 ADD_TO_TRACE: _POP_TOP (0, target=27, operand0=0, operand1=0)
Trace continuing
   7 ADD_TO_TRACE: _EXIT_TRACE (0, target=28, operand0=0, operand1=0)
Trace done
   8 ADD_TO_TRACE: _EXIT_TRACE (0, target=28, operand0=0, operand1=0)
Optimized trace (length 8):
   0 OPTIMIZED: _START_EXECUTOR_r00 (0, jump_target=7, operand0=0x7f098c755ff0, operand1=0)
   1 OPTIMIZED: _MAKE_WARM_r00 (0, target=0, operand0=0, operand1=0)
   2 OPTIMIZED: _SET_IP_r00 (0, target=27, operand0=0x7f098c758146, operand1=0)
   3 OPTIMIZED: _POP_TOP_NOP_r00 (0, target=27, operand0=0, operand1=0)
   4 OPTIMIZED: _SPILL_OR_RELOAD_r01 (0, target=0, operand0=0, operand1=0)
   5 OPTIMIZED: _POP_TOP_r10 (0, target=27, operand0=0, operand1=0)
   6 OPTIMIZED: _EXIT_TRACE_r00 (0, target=28, operand0=0x7f098c756050, operand1=0)
   7 OPTIMIZED: _DEOPT_r00 (0, target=27, operand0=0, operand1=0)