In a disassembled code:
movsx eax,[address1]
# a few fpu computations
dec eax
# so many fpu computations
jz label2
If fpu computations do not influence zero flag, then we can assume that it is equal to:
# a few fpu computations
# so many fpu computations
movsx eax,[address1]
dec eax
jz label2
Then, my question is that do mov
or dec
have any influence on zero flag?
Of course you should look this up in the manuals but here's a general rule:
So movsx
falls in the first category and will not change any flag.
But dec
clearly does a computation and most certainly changes several flags including the ZeroFlag.