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Diffstat (limited to 'lib/Target/WebAssembly/README.txt')
| -rw-r--r-- | lib/Target/WebAssembly/README.txt | 54 |
1 files changed, 41 insertions, 13 deletions
diff --git a/lib/Target/WebAssembly/README.txt b/lib/Target/WebAssembly/README.txt index 3433b1553e8c..ef0099f07efb 100644 --- a/lib/Target/WebAssembly/README.txt +++ b/lib/Target/WebAssembly/README.txt @@ -2,15 +2,42 @@ This WebAssembly backend is presently under development. -Currently the easiest way to use it is through Emscripten, which provides a -compilation environment that includes standard libraries, tools, and packaging -for producing WebAssembly applications that can run in browsers and other -environments. For more information, see the Emscripten documentation in -general, and this page in particular: +The most notable feature which is not yet stable is the ".o" file format. +".o" file support is needed for many common ways of using LLVM, such as +using it through "clang -c", so this backend is not yet considered widely +usable. However, this backend is usable within some language toolchain +packages: + +Emscripten provides a C/C++ compilation environment that includes standard +libraries, tools, and packaging for producing WebAssembly applications that +can run in browsers and other environments. For more information, see the +Emscripten documentation in general, and this page in particular: + * https://github.com/kripken/emscripten/wiki/New-WebAssembly-Backend + +Rust provides WebAssembly support integrated into Cargo. There are two +main options: + - wasm32-unknown-unknown, which provides a relatively minimal environment + that has an emphasis on being "native" + - wasm32-unknown-emscripten, which uses Emscripten internally and + provides standard C/C++ libraries, filesystem emulation, GL and SDL + bindings +For more information, see: + * https://www.hellorust.com/ + + +This backend does not yet support debug info. Full DWARF support needs a +design for how DWARF should be represented in WebAssembly. Sourcemap support +has an existing design and some corresponding browser implementations, so it +just needs implementing in LLVM. -Other ways of using this backend, such as via a standalone "clang", are also -under development, though they are not generally usable yet. +Work-in-progress documentation for the ".o" file format is here: + + * https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md + +A corresponding linker implementation is also under development: + + * https://lld.llvm.org/WebAssembly.html For more information on WebAssembly itself, see the home page: * https://webassembly.github.io/ @@ -30,6 +57,8 @@ turn red if not. Once most of these pass, further testing will use LLVM's own test suite. The tests can be run locally using: https://github.com/WebAssembly/waterfall/blob/master/src/compile_torture_tests.py +Some notes on ways that the generated code could be improved follow: + //===---------------------------------------------------------------------===// Br, br_if, and br_table instructions can support having a value on the value @@ -127,7 +156,7 @@ However, if moving the binary operator to its user moves it to a place where its operands can't be moved to, it would be better to leave it in place, or perhaps move it up, so that it can stackify its operands. A binary operator has two operands and one result, so in such cases there could be a net win by -prefering the operands. +preferring the operands. //===---------------------------------------------------------------------===// @@ -138,11 +167,10 @@ instructions advantageously for this purpose. //===---------------------------------------------------------------------===// -WebAssembly is now officially a stack machine, rather than an AST, and this -comes with additional opportunities for WebAssemblyRegStackify. Specifically, -the stack doesn't need to be empty after an instruction with no return values. -WebAssemblyRegStackify could be extended, or possibly rewritten, to take -advantage of the new opportunities. +WebAssemblyRegStackify currently assumes that the stack must be empty after +an instruction with no return values, however wasm doesn't actually require +this. WebAssemblyRegStackify could be extended, or possibly rewritten, to take +full advantage of what WebAssembly permits. //===---------------------------------------------------------------------===// |