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Intermediate Topic 27 of 50 Languages & Compilers

Three-Address Code

Simple IR with at most three operands per instruction.

How it works

Three-address code is an intermediate representation in which each instruction has at most three operands, typically a result and two sources, as in t1 = a + b. Complex expressions are broken into sequences of simple instructions using temporaries, and control flow is expressed with labels and jumps. It resembles assembly while staying machine independent, which makes optimization, analysis and instruction selection straightforward. Quadruples, triples and indirect triples are storage formats.

Step-by-step walkthrough

  1. Complex expressions are broken into simple steps.
  2. Each instruction has at most one operator and three addresses.
  3. t1 holds c times d.
  4. t2 adds b.
  5. It is easy to analyze and optimize.

Where it is used

Compilers translate expression trees into three-address code to apply constant folding, common subexpression elimination, dead code elimination and register allocation.

Common pitfall

Naively generated code has many redundant temporaries and copies that optimization must clean up. Handling short-circuit boolean expressions, array indexing and function calls needs care. Without SSA form, analyses must track variable redefinitions. Use consistent temporary naming and a control flow graph for global analysis.

Where it fits in the course

Three-Address Code is topic 27 of 50 in Languages & Compilers, rated Intermediate. It follows Intermediate Representations. The next topic is Static Single Assignment.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Languages & Compilers quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Three-Address Code?
Simple IR with at most three operands per instruction. It belongs to Languages & Compilers and is an intermediate-level topic.
Where do people use Three-Address Code?
Compilers translate expression trees into three-address code to apply constant folding, common subexpression elimination, dead code elimination and register allocation.
What is the most common mistake with Three-Address Code?
Naively generated code has many redundant temporaries and copies that optimization must clean up.
What should I learn before this topic?
Start with Intermediate Representations, the topic just before it in Languages & Compilers.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Languages & Compilers quiz.
Is Three-Address Code hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn Three-Address Code?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Three-Address Code?
Intermediate Representations, Static Single Assignment, Parser Generators are closely connected. The full list is in the related topics section of this page.
What should I study after Three-Address Code?
Continue with Static Single Assignment, the next topic in Languages & Compilers.

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