Fuchsia uses TLSDESC by default for all target architectures. We also
make the comment and check for hasDefaultTLSDESC more accurately reflect
its usage.
The implementation only enables when the `-enable-tlsdesc` option is
passed and the TLS model is `dynamic`.
LoongArch's GCC has the same option(-mtls-dialet=) as RISC-V.
Reviewers: heiher, MaskRay, SixWeining
Reviewed By: SixWeining, MaskRay
Pull Request: https://github.com/llvm/llvm-project/pull/90159
GCC supports -mtls-dialect= for several architectures to select TLSDESC.
This patch supports the following values
* x86: "gnu". "gnu2" (TLSDESC) is not supported yet.
* RISC-V: "trad" (general dynamic), "desc" (TLSDESC, see #66915)
AArch64 toolchains seem to support TLSDESC from the beginning, and the
general dynamic model has poor support. Nobody seems to use the option
-mtls-dialect= at all, so we don't bother with it.
There also seems very little interest in AArch32's TLSDESC support.
TLSDESC does not change IR, but affects object file generation. Without
a backend option the option is a no-op for in-process ThinLTO.
There seems no motivation to have fine-grained control mixing trad/desc
for TLS, so we just pass -mllvm, and don't bother with a modules flag
metadata or function attribute.
Co-authored-by: Paul Kirth <paulkirth@google.com>
