[WebAssembly] Don't inline -emscripten-cxx-exceptions-allowed functions

[aheejin]

Summary

Functions specified in -emscripten-cxx-exceptions-allowed, which is
set by Emscripten's EXCEPTION_CATCHING_ALLOWED setting, can be inlined
in LLVM middle ends before we reach WebAssemblyLowerEmscriptenEHSjLj
pass in the wasm backend and thus don't get transformed for exception
catching.

This fixes the issue by adding --force-attribute=FUNC_NAME:noinline
for each function name in -emscripten-cxx-exceptions-allowed, which
adds noinline attribute to the specified function and thus excludes
the function from inlining candidates in optimization passes.

Fixes the remaining half of
https://github.com/emscripten-core/emscripten/issues/10721.

[aheejin]

Comment fix

[sbc100]

Nice!

[aheejin]

Add break

clang/lib/Driver/ToolChains/WebAssembly.cpp

for (const Arg *A : DriverArgs.filtered(options::OPT_mllvm)) {
         getDriver().Diag(diag::err_drv_argument_not_allowed_with)
             << "-fwasm-exceptions"
             << "-mllvm -enable-emscripten-cxx-exceptions";
     }
     // '-fwasm-exceptions' implies exception-handling feature
     CC1Args.push_back("-target-feature");
     CC1Args.push_back("+exception-handling");
   }
+
+  for (const Arg *A : DriverArgs.filtered(options::OPT_mllvm)) {
+    StringRef Opt = A->getValue(0);
+    if (Opt.startswith("-emscripten-cxx-exceptions-allowed")) {
+      // '-mllvm -emscripten-cxx-exceptions-allowed' should be used with
+      // '-mllvm -enable-emscripten-cxx-exceptions'
+      bool EmExceptionArgExists = false;
+      for (const Arg *A : DriverArgs.filtered(options::OPT_mllvm)) {
+        if (StringRef(A->getValue(0)) == "-enable-emscripten-cxx-exceptions") {
+          EmExceptionArgExists = true;
+          break;
+        }
+      }
+      if (!EmExceptionArgExists)
+        getDriver().Diag(diag::err_drv_argument_only_allowed_with)
+            << "-mllvm -emscripten-cxx-exceptions-allowed"
+            << "-mllvm -enable-emscripten-cxx-exceptions";
+
+      // Prevent functions specified in -emscripten-cxx-exceptions-allowed list
+      // from being inlined before reaching the wasm backend.
+      StringRef FuncNamesStr = Opt.split('=').second;
+      SmallVector<StringRef, 4> FuncNames;
+      FuncNamesStr.split(FuncNames, ',');
+      for (auto Name : FuncNames) {
+        CC1Args.push_back("-mllvm");
+        CC1Args.push_back(DriverArgs.MakeArgString("--force-attribute=" + Name +
+                                                   ":noinline"));
+      }
+    }
+  }
 }
 
 ToolChain::RuntimeLibType WebAssembly::GetDefaultRuntimeLibType() const {
   return ToolChain::RLT_CompilerRT;
 }
 
 ToolChain::CXXStdlibType
 WebAssembly::GetCXXStdlibType(const ArgList &Args) const {

clang/test/Driver/wasm-toolchain.c

 // PTHREAD_NO_MUT_GLOBALS: invalid argument '-pthread' not allowed with '-mno-mutable-globals'
 
 // '-pthread' not allowed with '-mno-sign-ext'
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown \
 // RUN:     --sysroot=/foo %s -pthread -mno-sign-ext 2>&1 \
 // RUN:   | FileCheck -check-prefix=PTHREAD_NO_SIGN_EXT %s
 // PTHREAD_NO_SIGN_EXT: invalid argument '-pthread' not allowed with '-mno-sign-ext'
 
+// '-mllvm -emscripten-cxx-exceptions-allowed=foo,bar' sets
+// '-mllvm --force-attribute=foo:noinline -mllvm --force-attribute=bar:noinline'
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown \
+// RUN:    --sysroot=/foo %s -mllvm -enable-emscripten-cxx-exceptions \
+// RUN:    -mllvm -emscripten-cxx-exceptions-allowed=foo,bar 2>&1 \
+// RUN:  | FileCheck -check-prefix=EMSCRIPTEN_EH_ALLOWED_NOINLINE %s
+// EMSCRIPTEN_EH_ALLOWED_NOINLINE: clang{{.*}}" "-cc1" {{.*}} "-mllvm" "--force-attribute=foo:noinline" "-mllvm" "--force-attribute=bar:noinline"
+
+// '-mllvm -emscripten-cxx-exceptions-allowed' only allowed with
+// '-mllvm -enable-emscripten-cxx-exceptions'
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown \
+// RUN:     --sysroot=/foo %s -mllvm -emscripten-cxx-exceptions-allowed 2>&1 \
+// RUN:   | FileCheck -check-prefix=EMSCRIPTEN_EH_ALLOWED_WO_ENABLE %s
+// EMSCRIPTEN_EH_ALLOWED_WO_ENABLE: invalid argument '-mllvm -emscripten-cxx-exceptions-allowed' only allowed with '-mllvm -enable-emscripten-cxx-exceptions'
+
 // '-fwasm-exceptions' sets +exception-handling
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown \
 // RUN:    --sysroot=/foo %s -fwasm-exceptions 2>&1 \
 // RUN:  | FileCheck -check-prefix=WASM_EXCEPTIONS %s
 // WASM_EXCEPTIONS: clang{{.*}}" "-cc1" {{.*}} "-target-feature" "+exception-handling"
 
 // '-fwasm-exceptions' not allowed with '-mno-exception-handling'
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown \