In software engineering, retargeting is an attribute of software development tools that have been specifically designed to generate code for more than one computing platform.
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A retargetable compiler is a compiler that has been designed to be relatively easy to modify to generate code for different CPU instruction set architectures. The machine code produced by these is sometimes of lower quality than that produced by a compiler developed specifically for a single processor.
A retargetable compiler is a kind of cross compiler. Often (but not always) a retargetable compiler is portable (the compiler itself can run on several different CPUs) and self-hosting.
The goal of easily retargeting the compiler conflicts to some degree with the goal of providing fast execution and small code size. The optimization of code for some high performance processors requires a detailed and specific knowledge of the architecture and how the instructions are executed. The optimizations usually done by a retargetable compiler are only those applicable to any processor. This is unless developers have taken the large amount of time necessary to write a code generator specifically for an architecture.
A general-purpose global optimizer followed by machine-specific peephole optimization can work well.[1]
Examples of retargetable compilers:
Conversely, retargetable assemblers are capable of generating object files of different formats, which is useful in porting assembly language programs to various operating systems that run on the same CPU architecture (such as Windows and Linux on the x86 platform). NASM is one such assembler.