Semantic analysis is a critical phase in the compilation process, situated after syntax analysis and before code generation. It ensures that the parsed code adheres to the language’s semantic rules, focusing on meaning rather than structure. This phase verifies that the program’s operations are valid and logically consistent, setting the foundation for robust and error-free code execution. Let’s delve into its key components, including type checking, attribute grammars, symbol tables, and semantic errors.
Type Checking
Type checking ensures that operations in the code are applied to compatible data types. For example, assigning an integer value to a string variable or attempting arithmetic operations on incompatible types would raise errors. Type checking can be:
1. Static Type Checking
Conducted during compilation, it ensures type safety before the program runs. For instance:
int x = “hello”; // Compile-time error: incompatible types
2. Dynamic Type Checking
Performed at runtime, allowing more flexibility but with potential performance costs. For example:
x = 5
if isinstance(x, str):
print(x + ” world”)
—
Attribute Grammars
Attribute grammars extend context-free grammars to include semantic information, enabling rules to define attributes for grammar symbols. Attributes can be:
Synthesized Attributes: Derived from child nodes in the parse tree.
Inherited Attributes: Propagated from parent or sibling nodes.
For example, consider an expression grammar:
E -> E1 + T { E.val = E1.val + T.val }
E -> T { E.val = T.val }
T -> int { T.val = int.lexeme }
This grammar computes the value of an expression during parsing, blending syntactic structure with semantic meaning.
Symbol Tables
The symbol table is a core data structure that stores information about program identifiers, such as variables, functions, and classes. It maps names to their attributes, such as type, scope, and memory location. Consider the following C code:
int a = 10;
float b = 3.14;
The symbol table entries would be: | Name | Type | Scope | Value | |——|——–|———|——–| | a | int | global | 10 | | b | float | global | 3.14 |
Semantic Errors
Semantic errors violate logical correctness but are syntactically valid. Examples include:
Using undeclared variables:
int x = y + 1; // Error: y is undeclared
Type mismatches in function calls:
void foo(int x);
foo(“hello”); // Error: incompatible argument type
Accessing out-of-scope variables.
Semantic analysis ensures the program’s integrity by integrating type systems, grammars, and symbol tables while guarding against errors. It is a cornerstone of compiler design, enabling efficient and accurate program execution.
The article above is rendered by integrating outputs of 1 HUMAN AGENT & 3 AI AGENTS, an amalgamation of HGI and AI to serve technology education globally.