If you're compiling this from C source code, use the "__asm__
__volatile__ ("isync");" syntax. If you're generating straight LLVM
IR, then I'm not entirely sure. You'll have to create some type of
CallInst instruction. See TreeToLLVM::EmitASM_EXPR() in the LLVM-GCC
gcc/llvm-convert.cpp file for an example of how it generates one of
these.