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3 address code is a very common topic in many of the CS theories. I encountered it while studying Compiler Design. According to the Wikipedia article, it says -

Each TAC instruction has at most three operands and is typically a combination of assignment and a binary operator.

Now my query, does that mean I can assign a variable to another variable(operand) even if it doesn't changes any thing, as this action doesn't violates the exact meaning of TAC(at most three operands). Example for clarity:

a = b*c - d*4

TAC

t1 = b
t2 = c
t3 = d
t4 = t1*t2 
t5 = t3*4
t6 = t4 - t5
a = t6

In all the above lines, I haven't violated the TAC rule of at most 3 operands, but in the first 3 lines, I have assigned three variables to three different operands even if it isn't required.

Now technically will that be considered wrong? I know it's inefficient but is it wrong in technical terms? What I think is it's not wrong because the code optimization stage which comes after this will do the filtration if required. Still I want to know the opinions.

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Three address code is an intermediate language used internally by (some) compilers. What is "right" depends on the specific rules that that compiler expects/enforces. Efficiency, as you state, is normally not an issue, as the intermediate language is designed for easy massaging and ultimately traslating into efficient target code.

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