-fsplit-machine-functions is an optimization in codegen phase. when -flto is use, clang generate IR bitcode in .o files, and linker will call into these codegen optimization passes. Current clang driver doesn't pass this option to linker when both -fsplit-machine-functions and -flto are used, so the optimization is silently ignored. My fix generates linker option -plugin-opt=-split-machine-functions for this case. It allows the linker to pass "split-machine-functions" to code generator to turn on that optimization. It works for both gold and lld.
Reviewed By: hoy, wenlei
Differential Revision: https://reviews.llvm.org/D121969
Junfeng Dong