GCC compatibility provided by ARM® Compiler 6
The compiler in ARM Compiler 6 is based on Clang and LLVM technology. As such, it provides a high degree of compatibility with GCC.
ARM Compiler 6 can build the vast majority of C code that is written to be built with GCC. However, ARM Compiler is not 100% source compatible in all cases. Specifically, ARM Compiler does not aim to be bug-compatible with GCC. That is, ARM Compiler does not replicate GCC bugs.