[EH] Use LLVM implementation for new Wasm EH (#23469)

This adds a new `WASM` mode in `ExceptionLibrary`, which uses the new
standard Wasm (exnref) EH, adds a library variant for it, and make the
tests use the new LLVM implementation instead of the Binaryen
translator.

The CI won't pass until llvm/llvm-project#123915
lands.

This requires adding `-wasmexcept` and `-wasmsjlj` variants to
`MINIMAL_TASKS` in `embuilder.py`
because they are necessary to run coreX tests in CircleCI, because
dylink coreX tests in CircleCI rellies on `./embuilder build MINIMAL_PIC
--pic`, which is the sum of `MINIMAL_TASKS` and `MINIMAL_PIC_TASKS`.

Because a new variant is added to `ExceptionLibrary`, this increases
`SYSTEM` library size from 366M to 400M, roughly by 11%. We discussed
about the possibility of not shipping the exnref libraries and let them
be built on demand, but given that `SYSTEM` include all variants, I'm
not sure how we are going to do that:
https://github.com/emscripten-core/emscripten/blob/73ebb91029948e62b3a4cea9ccc8db2dd87162b5/embuilder.py#L174-L177

Author: aheejin

ChangeLog.md

@@ -20,6 +20,11 @@ See docs/process.md for more on how version tagging works.
 
 4.0.2 (in development)
 ----------------------
+- The standard Wasm EH, enabled by `-sWASM_LEGACY_EXCEPTIONS=0`, now uses the
+  LLVM backend implementation rather than the previously used Binaryen
+  translator
+  (https://github.com/WebAssembly/binaryen/blob/main/src/passes/TranslateEH.cpp).
+  (#23469) No specific action from the user is required.
 - Added support for compiling AVX2 intrinsics, 256-bit wide intrinsic is emulated
   on top of 128-bit Wasm SIMD instruction set. (#23035). Pass `-msimd128 -mavx2`
   to enable targeting AVX2.

embuilder.py

@@ -32,6 +32,7 @@
 MINIMAL_TASKS = [
     'libcompiler_rt',
     'libcompiler_rt-legacysjlj',
+    'libcompiler_rt-wasmsjlj',
     'libcompiler_rt-ww',
     'libc',
     'libc-debug',
@@ -40,13 +41,16 @@
     'libc_optz-debug',
     'libc++abi',
     'libc++abi-legacyexcept',
+    'libc++abi-wasmexcept',
     'libc++abi-noexcept',
     'libc++abi-debug',
     'libc++abi-debug-legacyexcept',
+    'libc++abi-debug-wasmexcept',
     'libc++abi-debug-noexcept',
     'libc++abi-debug-ww-noexcept',
     'libc++',
     'libc++-legacyexcept',
+    'libc++-wasmexcept',
     'libc++-noexcept',
     'libc++-ww-noexcept',
     'libal',
@@ -80,6 +84,7 @@
     'crt1_proxy_main',
     'crtbegin',
     'libunwind-legacyexcept',
+    'libunwind-wasmexcept',
     'libnoexit',
     'sqlite3',
     'sqlite3-mt',

site/source/docs/tools_reference/settings_reference.rst

@@ -1165,6 +1165,8 @@ https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-
 If false, emit instructions for the standardized exception handling proposal:
 https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/Exceptions.md
 
+.. note:: Applicable during both linking and compilation
+
 Default value: true
 
 .. _nodejs_catch_exit:

src/settings.js

@@ -781,7 +781,7 @@ var EXCEPTION_STACK_TRACES = false;
 // https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/legacy/Exceptions.md
 // If false, emit instructions for the standardized exception handling proposal:
 // https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/Exceptions.md
-// [link]
+// [compile+link]
 var WASM_LEGACY_EXCEPTIONS = true;
 
 // Emscripten throws an ExitStatus exception to unwind when exit() is called.

test/other/codesize/test_codesize_cxx_except_wasm.size

@@ -1 +1 @@
-144652
+144531

test/test_other.py

@@ -3535,7 +3535,10 @@ def test_embind_tsgen_jspi(self):
     'legacy': [1]
   })
   def test_embind_tsgen_exceptions(self, legacy):
+    if not legacy and shared.get_node_version(config.NODE_JS)[0] < 22:
+      self.skipTest('Node version needs to be 22 or greater to run tsgen with exnref')
     self.set_setting('WASM_LEGACY_EXCEPTIONS', legacy)
+
     # Check that when Wasm exceptions and assertions are enabled bindings still generate.
     self.run_process([EMXX, test_file('other/embind_tsgen.cpp'),
                       '-lembind', '-fwasm-exceptions', '-sASSERTIONS',

tools/building.py

@@ -93,6 +93,12 @@ def llvm_backend_args():
   elif settings.SUPPORT_LONGJMP == 'wasm':
     args += ['-wasm-enable-sjlj']
 
+  if settings.WASM_EXCEPTIONS:
+    if settings.WASM_LEGACY_EXCEPTIONS:
+      args += ['-wasm-use-legacy-eh']
+    else:
+      args += ['-wasm-use-legacy-eh=0']
+
   # better (smaller, sometimes faster) codegen, see binaryen#1054
   # and https://bugs.llvm.org/show_bug.cgi?id=39488
   args += ['-disable-lsr']
@@ -277,6 +283,10 @@ def link_lld(args, target, external_symbols=None):
 
   if settings.WASM_EXCEPTIONS:
     cmd += ['-mllvm', '-wasm-enable-eh']
+    if settings.WASM_LEGACY_EXCEPTIONS:
+      cmd += ['-mllvm', '-wasm-use-legacy-eh']
+    else:
+      cmd += ['-mllvm', '-wasm-use-legacy-eh=0']
   if settings.WASM_EXCEPTIONS or settings.SUPPORT_LONGJMP == 'wasm':
     cmd += ['-mllvm', '-exception-model=wasm']
 

tools/link.py

@@ -431,10 +431,6 @@ def check_human_readable_list(items):
     extras = settings.BINARYEN_EXTRA_PASSES.split(',')
     passes += [('--' + p) if p[0] != '-' else p for p in extras if p]
 
-  # Run the translator to the standardized EH instructions.
-  if not settings.WASM_LEGACY_EXCEPTIONS:
-    passes += ['--emit-exnref']
-
   # If we are going to run metadce then that means we will be running binaryen
   # tools after the main invocation, whose flags are determined here
   # (specifically we will run metadce and possibly also wasm-opt for import/

tools/settings.py

@@ -84,6 +84,7 @@
     'INLINING_LIMIT',
     'DISABLE_EXCEPTION_CATCHING',
     'DISABLE_EXCEPTION_THROWING',
+    'WASM_LEGACY_EXCEPTIONS',
     'MAIN_MODULE',
     'SIDE_MODULE',
     'RELOCATABLE',

tools/shared.py

@@ -379,11 +379,13 @@ def node_reference_types_flags(nodejs):
 
 def node_exception_flags(nodejs):
   node_version = get_node_version(nodejs)
-  # Exception handling was enabled by default in node v17.
+  # Legacy exception handling was enabled by default in node v17.
   if node_version and node_version < (17, 0, 0):
     return ['--experimental-wasm-eh']
-  else:
-    return []
+  # Standard exception handling was supported behind flag in node v22.
+  if node_version and node_version >= (22, 0, 0) and not settings.WASM_LEGACY_EXCEPTIONS:
+    return ['--experimental-wasm-exnref']
+  return []
 
 
 def node_pthread_flags(nodejs):