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This had a large performance penalty of between a factor 10 and 20 for Java versus C in average applications. [5] To combat this, a just-in-time (JIT) compiler was introduced into Java 1.1. Due to the high cost of compiling, an added system called HotSpot was introduced in Java 1.2 and was made the default in Java 1.3.
To optimize this, a C++ compiler would need to: Inline the sin and operator+ function calls. Fuse the loops into a single loop. Remove the unused stores into the temporary arrays (can use a register or stack variable instead). Remove the unused allocation and free. All of these steps are individually possible.
Here is an example of ANSI C code that will generally cause a segmentation fault on platforms with memory protection. It attempts to modify a string literal, which is undefined behavior according to the ANSI C standard. Most compilers will not catch this at compile time, and instead compile this to executable code that will crash:
In some languages (e.g. Java [9]) some forms of unreachable code are explicitly disallowed. The optimization that removes unreachable code is known as dead code elimination . Code may become unreachable as a consequence of transformations performed by an optimizing compiler (e.g., common subexpression elimination ).
This also implies that C++ compilers can automatically select the most efficient representation for the target platform (i.e., 64-bit integers for a 64-bit platform), while the representation is fixed in Java, meaning the values can either be stored in the less-efficient size, or must pad the remaining bits and add code to emulate the reduced ...
Heap modeling: Run-time allocations may be abstracted by: their allocation sites (the statement or instruction that performs the allocation, e.g., a call to malloc or an object constructor), a more complex model based on a shape analysis, the type of the allocation, or; one single allocation (this is called heap-insensitivity).
Java 5 Update 5 (1.5.0_05) is the last release of Java to work on Windows 95 (with Internet Explorer 5.5 installed) and Windows NT 4.0. [36] Java 5 was first available on Apple Mac OS X 10.4 (Tiger) [37] and was the default version of Java installed on Apple Mac OS X 10.5 (Leopard). Public support and security updates for Java 1.5 ended in ...