While Clang/LLVM is cool, this is more of a pure business decision. IBM supports multiple compiler toolchains: XL C/C++/FORTRAN, GCC, Java, COBOL, etc... So,

While Clang/LLVM is cool, this is more of a pure business decision. IBM supports multiple compiler toolchains: XL C/C++/FORTRAN, GCC, Java, COBOL, etc... So, when a customer comes by with a codebase and wants to run it on their System x/System p/System z big iron, IBM's response needs to be a simple "Yes" when it comes to support. Customer A has used XL since the epoch of computing, cool, that's supported. Customer B has codebase tuned and littered with GCC attributes, cool, that's supported as well. Customer C wants Clang/LLVM because devs find it easier to debug and it's growing in features, cool, that will be supported as well.