LOAD_FAST_BORROW not being used even when safe to do so, if value is live at BB end. #133672
Description
This function
def f(x, y, c):
return 1 + (x if c else y)
compiles to
1 RESUME 0
2 LOAD_SMALL_INT 1
LOAD_FAST_BORROW 2 (c)
TO_BOOL
POP_JUMP_IF_FALSE 9 (to L1)
NOT_TAKEN
LOAD_FAST_BORROW 0 (x)
BINARY_OP 0 (+)
RETURN_VALUE
L1: LOAD_FAST 1 (y)
BINARY_OP 0 (+)
RETURN_VALUE
Note that the load of y uses LOAD_FAST even though LOAD_FAST_BORROW is safe.
This becomes important with virtual iterators as the iterable for the loop is live at BB end.