🧠 Target Language and Addresses in Target Code (Compiler Construction)

This topic belongs to the Code Generation phase of a compiler. It explains what the final output language is and how memory locations (addresses) are represented in generated code.

---

📌 1. Target Language

📖 Definition

The target language is the language into which a compiler translates the source program.

👉 It is the final output language of the compiler.

---

🧠 Types of Target Language

🔹 1. Machine Language

• Binary instructions (0s and 1s)
• Directly executed by CPU

🔹 2. Assembly Language (Most Common)

• Uses mnemonics like MOV, ADD, MUL
• Easier to read than machine code

🔹 3. Intermediate Target Code

• Sometimes pseudo-assembly is used before final machine code

---

📊 Example

Source Code:

x = a + b;

Target (Assembly Code):

MOV R1, a
ADD R1, b
MOV x, R1

---

⭐ Key Points (Exam Important)

✔ Target language is final output of compiler ✔ Can be machine code or assembly code ✔ Must be efficient and executable ✔ Depends on target machine architecture

---

🧠 2. Addresses in Target Code

📖 Definition

Addresses in target code refer to the locations where data is stored or accessed during execution.

👉 These may represent:

• Memory locations
• Registers
• Stack locations
• Labels (for jumps)

---

🧠 3. Types of Addresses

🔹 1. Absolute Address

📖 Definition

Fixed memory location in physical memory.

Example:

MOV R1, 5000

👉 5000 = fixed memory address

---

🔹 2. Relative Address

📖 Definition

Address relative to a base register or current instruction.

Example:

LOAD R1, 8(R2)

👉 Means: R2 + 8

---

🔹 3. Symbolic Address

📖 Definition

Uses labels instead of actual memory locations.

Example:

L1: ADD R1, R2
JMP L1

---

🔹 4. Register Address

📖 Definition

Uses CPU registers instead of memory.

Example:

MOV R1, R2

---

🧠 4. Addressing Modes in Target Code

Addressing modes define how operands are accessed.

---

🔹 1. Immediate Addressing

Operand is given directly.

MOV R1, #5

---

🔹 2. Direct Addressing

Memory address is given.

MOV R1, A

---

🔹 3. Indirect Addressing

Address stored in a pointer/register.

MOV R1, (R2)

---

🔹 4. Indexed Addressing

Base + offset form.

MOV R1, 4(R2)

---

🧠 5. Address Representation in Compiler

During code generation, compiler assigns:

🔹 Variables → Memory addresses

a → 1000
b → 1004
c → 1008

---

🔹 Temporary Variables

Created during intermediate code:

t1 = a + b
t1 → register or stack memory

---

🔹 Labels for Control Flow

L1, L2, L3

Used in:

• loops
• if-else
• switch

---

🧠 6. Example of Address Translation

Source Code:

if (a < b)
   x = a + b;

---

Intermediate Code:

if a < b goto L1
goto L2
L1: t1 = a + b
    x = t1
L2:

---

Target Code:

MOV R1, a
CMP R1, b
JGE L2

MOV R2, a
ADD R2, b
MOV x, R2

L2:

---

🧠 7. Importance of Addresses in Code Generation

✔ Helps map variables to memory ✔ Enables correct execution flow ✔ Required for jumps and loops ✔ Used for register allocation ✔ Improves efficiency of target code

---

🧠 8. Relocation of Addresses

📖 Definition

Relocation means adjusting addresses when program is loaded into memory.

---

Types:

• Compile-time relocation
• Load-time relocation
• Run-time relocation

---

📊 9. Target Language vs Address Types

Concept	Meaning
Target language	Final output (assembly/machine code)
Absolute address	Fixed memory location
Relative address	Base + offset
Symbolic address	Label-based reference
Register address	CPU register usage

---

📌 10. Key Exam Points

✔ Target language is final compiler output ✔ Usually assembly or machine code ✔ Addresses define memory locations of data ✔ Types: absolute, relative, symbolic, register ✔ Addressing modes control how operands are accessed ✔ Labels are used for control flow

---

🎯 Final Exam Definition

Target language is the final language produced by a compiler, usually assembly or machine code. Addresses in target code refer to the memory locations, registers, or labels used to access data and control program execution. These addresses may be absolute, relative, symbolic, or register-based depending on the addressing mode used.

---

📊 FINAL REVISION TABLE

Concept	Description	Example
Target language	Final output code	Assembly code
Absolute address	Fixed memory	5000
Relative address	Base + offset	8(R2)
Symbolic address	Labels	L1, L2
Register address	CPU registers	R1, R2
Immediate mode	Constant value	#5

---