[WebAssembly] supports -stdlib=libc++ switch

[patcheng]

Summary

Referenced implementation from Fuchsia and Darwin Toolchain.

Still only support CST_Libcxx.

Now checks that the argument is really '-stdlib=libc++', and display error.

Also, now will pass -lc++ and -lc++abi to the linker.

[sbc100]

Nice. I happened to just upload a similar (but orthogonal) patch: https://reviews.llvm.org/D41966

[dschuff]

LGTM, but does it need to be rebased after the -allow-undefined-file change?

[sbc100]

lib/Driver/ToolChains/WebAssembly.cpp

151

Can you add -lc++abi too? Then I can drop D41966

[patcheng]

lib/Driver/ToolChains/WebAssembly.cpp

151

Sure, but I am not in front of a computer with the code at the moment.

I should be able to get this done later this evening (PST).

[patcheng]

Added -lc++abi per @sbc100 's suggestion

[sbc100]

lgtm

[patcheng]

Thanks @sbc100.

BTW I don't have commit access. When it's ready to be committed, I would need help with that.

Thanks

lib/Driver/ToolChains/WebAssembly.h

   void AddClangCXXStdlibIncludeArgs(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
+  void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
+                           llvm::opt::ArgStringList &CmdArgs) const override;
   std::string getThreadModel() const override;
 
   const char *getDefaultLinker() const override {

lib/Driver/ToolChains/WebAssembly.cpp

 #include "CommonArgs.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
+#include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "llvm/Option/ArgList.h"
 

 }
 
 ToolChain::CXXStdlibType WebAssembly::GetCXXStdlibType(const ArgList &Args) const {
+  if (Arg *A = Args.getLastArg(options::OPT_stdlib_EQ)) {
+    StringRef Value = A->getValue();
+    if (Value != "libc++")
+      getDriver().Diag(diag::err_drv_invalid_stdlib_name)
+        << A->getAsString(Args);
+  }
   return ToolChain::CST_Libcxx;
 }
 

                      getDriver().SysRoot + "/include/c++/v1");
 }
 
+void WebAssembly::AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
+                           llvm::opt::ArgStringList &CmdArgs) const {
+
+  switch (GetCXXStdlibType(Args)) {
+  case ToolChain::CST_Libcxx:
+    CmdArgs.push_back("-lc++");
+    CmdArgs.push_back("-lc++abi");
+    break;
+  case ToolChain::CST_Libstdcxx:
+    llvm_unreachable("invalid stdlib name");
+  }
+}
+
 std::string WebAssembly::getThreadModel() const {
   // The WebAssembly MVP does not yet support threads; for now, use the
   // "single" threading model, which lowers atomics to non-atomic operations.

test/Driver/wasm-toolchain.cpp

+// A basic clang -cc1 command-line. WebAssembly is somewhat special in
+// enabling -ffunction-sections, -fdata-sections, and -fvisibility=hidden by
+// default.
+
+// RUN: %clang++ %s -### -no-canonical-prefixes -target wasm32-unknown-unknown 2>&1 | FileCheck -check-prefix=CC1 %s
+// CC1: clang{{.*}} "-cc1" "-triple" "wasm32-unknown-unknown" {{.*}} "-fvisibility" "hidden" {{.*}} "-ffunction-sections" "-fdata-sections"
+
+// Ditto, but ensure that a user -fno-function-sections disables the
+// default -ffunction-sections.
+
+// RUN: %clang++ %s -### -target wasm32-unknown-unknown -fno-function-sections 2>&1 | FileCheck -check-prefix=NO_FUNCTION_SECTIONS %s
+// NO_FUNCTION_SECTIONS-NOT: function-sections
+
+// Ditto, but ensure that a user -fno-data-sections disables the
+// default -fdata-sections.
+
+// RUN: %clang++ %s -### -target wasm32-unknown-unknown -fno-data-sections 2>&1 | FileCheck -check-prefix=NO_DATA_SECTIONS %s
+// NO_DATA_SECTIONS-NOT: data-sections
+
+// Ditto, but ensure that a user -fvisibility=default disables the default
+// -fvisibility=hidden.
+
+// RUN: %clang++ %s -### -target wasm32-unknown-unknown -fvisibility=default 2>&1 | FileCheck -check-prefix=FVISIBILITY_DEFAULT %s
+// FVISIBILITY_DEFAULT-NOT: hidden
+
+// A basic C++ link command-line.
+
+// RUN: %clang++ -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo --stdlib=c++ %s 2>&1 | FileCheck -check-prefix=LINK %s
+// LINK: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
+// LINK: lld{{.*}}" "-flavor" "wasm" "-L/foo/lib" "crt1.o" "[[temp]]" "-lc++" "-lc++abi" "-allow-undefined-file" "wasm.syms" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
+
+// A basic C++ link command-line with optimization.
+
+// RUN: %clang++ -### -O2 -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s --stdlib=c++ 2>&1 | FileCheck -check-prefix=LINK_OPT %s
+// LINK_OPT: clang{{.*}}" "-cc1" {{.*}} "-o" "[[temp:[^"]*]]"
+// LINK_OPT: lld{{.*}}" "-flavor" "wasm" "-L/foo/lib" "crt1.o" "[[temp]]" "-lc++" "-lc++abi" "-allow-undefined-file" "wasm.syms" "-lc" "{{.*[/\\]}}libclang_rt.builtins-wasm32.a" "-o" "a.out"
+