Currently clangDriver passes -femulated-tls and -fno-emulated-tls to cc1.
cc1 forwards the option to LLVMCodeGen and ExplicitEmulatedTLS is used
to decide the value. Simplify this by moving the Clang decision to
clangDriver and moving the LLVM decision to InitTargetOptionsFromCodeGenFlags.
Currently the driver does not propagate the `-f[no-]emulated-tls` flags
to the linker under LTO. This can be surprising when the platform
defaults differ from the flags being passed. A related discussion can be
found in https://reviews.llvm.org/D143619. While the focus there was
RISC-V support, the root cause was that setting `-femualted-tls` and
`-flto` when compiling with Clang resulted in missing symbols because
the platform defaults for Android differed from the flags being passed
to Clang.
This patch changes the Clang driver's behavior to pass the emulated-tls
flags through to the linker when compiling with LTO/ThinLTO.
Reviewed By: phosek, vit9696
Differential Revision: https://reviews.llvm.org/D147834
Since LLVM r326341, default EmulatedTLS mode is decided in backend
according to target triple. Any front-end should pass -f[no]-emulated-tls
to backend and set up ExplicitEmulatedTLS only when the flags are used.
Differential Revision: https://reviews.llvm.org/D43965
llvm-svn: 326499
FIXME: Add more targets to use emutls into clang/test/Driver/emulated-tls.cpp.
FIXME: Add cygwin tests into llvm/test/CodeGen/X86. Working in progress.
llvm-svn: 257984
