IBM XL C C Compilers

XL C/C++ is the name of IBM's proprietary optimizing C/C++ compiler for IBM-supported environments.

The IBM XL compilers are built from modularized components consisting of front ends (for different programming languages), a platform agnostic high level optimizer, and platform-specific low-level optimizers/code generators to target specific hardware and operating systems. The XL C/C++ compilers target POWER, BlueGene/Q, and z Systems hardware architectures.

A common high level optimizer across the POWER and z/OS XL C/C++ compilers optimizes the source program using platform-agnostic optimizations such as inter-procedural analysis, profile-directed feedback, and loop and vector optimizations.

A low-level optimizer on each platform performs function-level optimizations, and generates optimized code for a specific operating system and hardware platform.

The particular optimizations performed for any given compilation depend upon the optimization level chosen under option control (O2 to O5) along with any other optimization-related options, such as those for interprocedural analysis or loop optimizations.

A 60-day installable evaluation version is available for download for the XL C/C++ for AIX, XL C/C++ for Linux on Power, and XL C/C++ for Linux on z compilers. z/OS XL C/C++ is available for a 15-day zero install trial via the IBM Integrated Solution for z Systems Development.

In June 2016, IBM introduced XL C/C++ for Linux Community Edition which is free of charge. It can be downloaded from this link.

The XL compilers on AIX have delivered leadership scores in the SPEC CPU2000 and CPU2006 benchmarks, in combination with specific IBM POWER system processor announcements, for example CPU2006 Floating Point score of 71.5 in May 2010 and SPEC CPU2000 Floating Point score of 4051 in August 2006.

Current (2016) versions of the XL C/C++ compilers support a subset of the C++03 standard on AIX; while XL C/C++ for Linux (Power) v13.1.3 supports C++11.

The XL C/C++ compiler for Linux on Power little endian edition, released in December 2014, is based on the open source Clang front end (part of the Clang/LLVM open source project) and therefore provides a higher level of language and GCC compatibility than IBM C/C++ compilers on other platforms, although that support is a subset of what Clang/LLVM itself supports.