GATE Computer Science Engineering(CSE) 2027 Test: Code Generation & Optimization-

The phases of compiler
1. Lexical
2. Syntax
3. Semantic
4. Intermediate code generation, are all machine dependent phases and are not relocatable.
The together make pass-1 of the compiler. This program hence can not be made to execute in any area of storage other than the one designated for it at the time of its coding or translation.

The self relocating program is one which can itself perform the relocation of its address sensitive portion. Code-optimization and target code generation comes under the pass-2 of the compiler and is machine independent.

Option C is correct.

Abstract machine model provides a machine-independent representation so the front end can generate a single intermediate code that is not tied to any real machine.

This improves portability because the same front end can be paired with different back ends (target code generators) for different machines without changing the front end.

Although syntax-directed translations can be used to produce intermediate code, that statement (Option B) is a general fact about implementation technique and does not specifically capture the benefit of using an abstract machine model for portability, which is the key point here.

Option A is incorrect because lexical and syntax analysis are performed before intermediate code generation; choosing an abstract machine model does not make these analyses easier.

Option D is incorrect because it is possible to generate code directly for real machines; using an intermediate representation is a design choice to improve modularity and portability, not because direct generation is impossible.

Therefore, Option C best answers the question.

The preorder expansion can be represented as 

$ + x*yz* + xyz

Quadruples is not the intermediate code form.

Properties of a basic block are as follows:

• The flow of control can only enter the basic block through the first instruction in the block.
• No numps in the middle of the block.
• Control leaves the block without halting/branching.

The basic blocks become the nodes of a flow graph, whose edges indicate which blocks can follows which other blocks.

The graph that shows the basic blocks and their successor relationship is called control graph.

(a) i%2 is inner loop invariant, it can be moved before inner loop.
(b) 4*j is common sub-expression-appeared in two statements.
(c) 4*j can be reduced to j<<2 by strength reduction.
(d) There is no dead code in given code segment. So there is no scope of dead code elimination in this code.
Hence only option (d) is FALSE.

Some code optimizations are carried out on the intermediate code because program analysis is more accurate on intermediate code than on machine code.

Runtime environment means we deal with dynamic memory allocation and Heap is a dynamic data structure.
So it is clear that those languages that allow dynamic data structure necessarily need heap allocation in the runtime environment.