SuccessChanges

Summary

  1. [WebAssembly] Compile all TLS on Emscripten as local-exec Summary: Currently, on Emscripten, dynamic linking is not supported with threads. This means that if thread-local storage is used, it must be used in a statically-linked executable. Hence, local-exec is the only possible model. This diff compiles all TLS variables to use local-exec on Emscripten as a temporary measure until dynamic linking is supported with threads. The goal for this is to allow C++ types with constructors to be thread-local. Currently, when `clang` compiles a `thread_local` variable with a constructor, it generates `__tls_guard` variable: @__tls_guard = internal thread_local global i8 0, align 1 As no TLS model is specified, this is treated as general-dynamic, which we do not support (and cannot support without implementing dynamic linking support with threads in Emscripten). As a result, any C++ constructor in `thread_local` variables would not compile. By compiling all `thread_local` as local-exec, `__tls_guard` will compile and we can support C++ constructors with TLS without implementing dynamic linking with threads. Depends on D64537 Reviewers: tlively, aheejin, sbc100 Reviewed By: aheejin Subscribers: dschuff, jgravelle-google, hiraditya, sunfish, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D64776
Revision 366275 by quantum:
[WebAssembly] Compile all TLS on Emscripten as local-exec

Summary:
Currently, on Emscripten, dynamic linking is not supported with threads.
This means that if thread-local storage is used, it must be used in a
statically-linked executable. Hence, local-exec is the only possible model.

This diff compiles all TLS variables to use local-exec on Emscripten as a
temporary measure until dynamic linking is supported with threads.

The goal for this is to allow C++ types with constructors to be thread-local.

Currently, when `clang` compiles a `thread_local` variable with a constructor,
it generates `__tls_guard` variable:

    @__tls_guard = internal thread_local global i8 0, align 1

As no TLS model is specified, this is treated as general-dynamic, which we do
not support (and cannot support without implementing dynamic linking support
with threads in Emscripten). As a result, any C++ constructor in `thread_local`
variables would not compile.

By compiling all `thread_local` as local-exec, `__tls_guard` will compile and
we can support C++ constructors with TLS without implementing dynamic linking
with threads.

Depends on D64537

Reviewers: tlively, aheejin, sbc100

Reviewed By: aheejin

Subscribers: dschuff, jgravelle-google, hiraditya, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64776
Change TypePath in RepositoryPath in Workspace
The file was modified/llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp (diff)llvm.src/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp
The file was added/llvm/trunk/test/CodeGen/WebAssembly/tls-general-dynamic.llllvm.src/test/CodeGen/WebAssembly/tls-general-dynamic.ll
The file was added/llvm/trunk/test/CodeGen/WebAssembly/tls-local-exec.llllvm.src/test/CodeGen/WebAssembly/tls-local-exec.ll
The file was removed/llvm/trunk/test/CodeGen/WebAssembly/tls.llllvm.src/test/CodeGen/WebAssembly/tls.ll