[PATCH] D64537: [WebAssembly] Implement thread-local storage for non-PIC cases

[Guanzhong Chen via Phabricator via cfe-commits]

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Need to add tests for the compiler intrinsic `__builtin_wasm_tls_size`.


Thread local variables are placed inside a `.tdata` segment. Their symbols are
offsets from the start of the segment. The address of a thread local variable
is computed as `__tls_base` + the offset from the start of the segment.

`.tdata` segment is a passive segment and `memory.init` is used once per thread
to initialize the thread local storage.

`__tls_base` is a wasm global. Since each thread has its own wasm instance,
it is effectively thread local. Currently, `__tls_base` must be initialized
at thread startup, and so cannot be used with dynamic libraries.

`__tls_base` is to be initialized with a new linker-synthesized function,
`__wasm_init_tls`, which takes as an argument a block of memory to use as the
storage for thread locals. It then initializes the block of memory and sets
`__tls_base`.

To help allocating memory for thread-local storage, a new compiler intrinsic
is introduced: `__builtin_wasm_tls_size()`. This instrinsic function returns
the size of the thread-local storage for the current function.

The expected usage is to run something like the following upon thread startup:

  __wasm_init_tls(calloc(__builtin_wasm_tls_size(), 1));


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D64537

Files:
  clang/include/clang/Basic/BuiltinsWebAssembly.def
  clang/lib/CodeGen/CGBuiltin.cpp
  lld/test/wasm/data-layout.ll
  lld/test/wasm/gc-sections.ll
  lld/test/wasm/tls.ll
  lld/wasm/Driver.cpp
  lld/wasm/Symbols.cpp
  lld/wasm/Symbols.h
  lld/wasm/Writer.cpp
  llvm/include/llvm/BinaryFormat/Wasm.h
  llvm/include/llvm/IR/IntrinsicsWebAssembly.td
  llvm/include/llvm/MC/MCSectionWasm.h
  llvm/lib/MC/WasmObjectWriter.cpp
  llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
  llvm/lib/Target/WebAssembly/WebAssemblyISD.def
  llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
  llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h
  llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
  llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp
  llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
  llvm/test/CodeGen/WebAssembly/target-features-tls.ll
  llvm/test/CodeGen/WebAssembly/tls.ll

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