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Example of branch table in Wikibooks for IBM S/360; Examples of, and arguments for, Jump Tables via Function Pointer Arrays in C/C++; Example code generated by 'Switch/Case' branch table in C, versus IF/ELSE. Example code generated for array indexing if structure size is divisible by powers of 2 or otherwise.
Switch statements (or case statements, or multiway branches) compare a given value with specified constants and take action according to the first constant to match. There is usually a provision for a default action ("else", "otherwise") to be taken if no match succeeds. Switch statements can allow compiler optimizations, such as lookup tables.
A lookup table, which contains, as keys, the case values and, as values, the part under the case statement. (In some languages, only actual data types are allowed as values in the lookup table. In other languages, it is also possible to assign functions as lookup table values, gaining the same flexibility as a real switch statement.
For C and C++, the compiler is allowed to give a compile-time diagnostic in these cases, but is not required to: the implementation will be considered correct whatever it does in such cases, analogous to don't-care terms in digital logic. It is the responsibility of the programmer to write code that never invokes undefined behavior, although ...
In computing, inline expansion, or inlining, is a manual or compiler optimization that replaces a function call site with the body of the called function. Inline expansion is similar to macro expansion, but occurs during compilation, without changing the source code (the text), while macro expansion occurs prior to compilation, and results in different text that is then processed by the compiler.
Φ functions are not implemented as machine operations on most machines. A compiler can implement a Φ function by inserting "move" operations at the end of every predecessor block. In the example above, the compiler might insert a move from y 1 to y 3 at the end of the middle-left block and a move from y 2 to y 3 at the
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In this case it is "d=b" (l.7) Search for the first time the variable is read. In this case it is "return d" Write down this information in the following style: [name of the variable you are creating a def-use-chain for, the concrete write access, the concrete read access] In this case it is: [d, d=b, return d]