Project ForgeCompiler Design
Code Generation & Optimization
GATE 2014
Medium
Which one of the following is FALSE?
- AA basic block is a sequence of instructions where control enters the sequence at the beginning and exits at the end.
- BAvailable expression analysis can be used for common subexpression elimination.
- CLive variable analysis can be used for dead code elimination.
- x = 4*5 ⇒ x = 20 is an example of common subexpression elimination.
Explanation
A, B, and C are all standard, correct compiler-optimization facts. D mislabels the optimization: replacing 'x=4*5' with 'x=20' (evaluating a constant expression at compile time) is CONSTANT FOLDING, not common subexpression elimination (which reuses an already-computed value for a repeated expression).
Source: GATE CS 2014 (Session 1) (2014)
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