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Conversely, loop fusion (or loop jamming) is a compiler optimization and loop transformation which replaces multiple loops with a single one. [3] [2] Loop fusion does not always improve run-time speed. On some architectures, two loops may actually perform better than one loop because, for example, there is increased data locality within
In computing, C localization functions are a group of functions in the C programming language implementing basic localization routines. [1] [2] The functions are used in multilingual programs to adapt to the specific locale. In particular, the way of displaying of numbers and currency can be modified.
System cost or reliability may be more important than the code speed. For example, compilers for embedded software usually offer options that reduce code size at the expense of speed. The code's timing may need to be predictable, rather than as fast as possible, so code caching might be disabled, along with compiler optimizations that require it.
Vectorization – attempts to run as many of the loop iterations as possible at the same time on a SIMD system. Unrolling – duplicates the body of the loop multiple times, in order to decrease the number of times the loop condition is tested and the number of jumps, which may degrade performance by impairing the instruction pipeline.
A run-time system can inline function as well. Run-time inlining can use dynamic profiling information to make better decisions about which functions to inline, as in the Java Hotspot compiler. [9] Here is a simple example of inline expansion performed "by hand" at the source level in the C programming language:
Despite the seemingly greater complexity of the second example, it may actually run faster on modern CPUs because they use an instruction pipeline. By nature, any jump in the code causes a pipeline stall, which is a detriment to performance. Additionally, loop inversion allows safe loop-invariant code motion.
Loop unrolling, also known as loop unwinding, is a loop transformation technique that attempts to optimize a program's execution speed at the expense of its binary size, which is an approach known as space–time tradeoff. The transformation can be undertaken manually by the programmer or by an optimizing compiler.
A diagram depicting an optimizing compiler removing a potentially useless call to assembly instruction "b" by sinking it to its point of use. Code Sinking, also known as lazy code motion, is a term for a technique that reduces wasted instructions by moving instructions to branches in which they are used: [1] If an operation is executed before a branch, and only one of the branch paths use the ...