[WebAssembly] Make thread-related options consistent

Summary:
There have been three options related to threads and users had to set
all three of them separately to get the correct compilation results.
This makes sure the relationship between the options makes sense and
sets necessary options for users if only part of the necessary options
are specified. This does:

- Remove `-matomics`; this option alone does not enable anything, so
  removed it to not confuse users.
- `-mthread-model posix` sets `-target-feature +atomics`
- `-pthread` sets both `-target-feature +atomics` and
  `-mthread-model posix`
Also errors out when explicitly given options don't match, such as
`-pthread` is given with `-mthread-model single`.

Reviewers: dschuff, sbc100, tlively, sunfish

Subscribers: jgravelle-google, jfb, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D57874

llvm-svn: 353761

clang/include/clang/Driver/Options.td

@@ -2160,8 +2160,6 @@ def mexception_handing : Flag<["-"], "mexception-handling">, Group<m_wasm_Featur
 def mno_exception_handing : Flag<["-"], "mno-exception-handling">, Group<m_wasm_Features_Group>;
 def mbulk_memory : Flag<["-"], "mbulk-memory">, Group<m_wasm_Features_Group>;
 def mno_bulk_memory : Flag<["-"], "mno-bulk-memory">, Group<m_wasm_Features_Group>;
-def matomics : Flag<["-"], "matomics">, Group<m_wasm_Features_Group>;
-def mno_atomics : Flag<["-"], "mno-atomics">, Group<m_wasm_Features_Group>;
 
 def mamdgpu_debugger_abi : Joined<["-"], "mamdgpu-debugger-abi=">,
   Flags<[HelpHidden]>,

clang/include/clang/Driver/ToolChain.h

@@ -453,7 +453,9 @@ class ToolChain {
   virtual bool SupportsEmbeddedBitcode() const { return false; }
 
   /// getThreadModel() - Which thread model does this target use?
-  virtual std::string getThreadModel() const { return "posix"; }
+  virtual std::string getThreadModel(const llvm::opt::ArgList &) const {
+    return "posix";
+  }
 
   /// isThreadModelSupported() - Does this target support a thread model?
   virtual bool isThreadModelSupported(const StringRef Model) const;

clang/lib/Driver/Driver.cpp

@@ -1528,7 +1528,7 @@ void Driver::PrintVersion(const Compilation &C, raw_ostream &OS) const {
     if (TC.isThreadModelSupported(A->getValue()))
       OS << "Thread model: " << A->getValue();
   } else
-    OS << "Thread model: " << TC.getThreadModel();
+    OS << "Thread model: " << TC.getThreadModel(C.getArgs());
   OS << '\n';
 
   // Print out the install directory.

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3823,7 +3823,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back(A->getValue());
   }
   else
-    CmdArgs.push_back(Args.MakeArgString(TC.getThreadModel()));
+    CmdArgs.push_back(Args.MakeArgString(TC.getThreadModel(Args)));
 
   Args.AddLastArg(CmdArgs, options::OPT_fveclib);
 

clang/lib/Driver/ToolChains/WebAssembly.cpp

@@ -20,6 +20,27 @@ using namespace clang::driver::toolchains;
 using namespace clang;
 using namespace llvm::opt;
 
+void parseThreadArgs(const Driver &Driver, const ArgList &DriverArgs,
+                     bool &Pthread, StringRef &ThreadModel,
+                     bool CheckForErrors = true) {
+  // Default value for -pthread / -mthread-model options, each being false /
+  // "single".
+  Pthread =
+      DriverArgs.hasFlag(options::OPT_pthread, options::OPT_no_pthread, false);
+  ThreadModel =
+      DriverArgs.getLastArgValue(options::OPT_mthread_model, "single");
+  if (!CheckForErrors)
+    return;
+
+  // Did user explicitly specify -mthread-model / -pthread?
+  bool HasThreadModel = DriverArgs.hasArg(options::OPT_mthread_model);
+  bool HasPthread = Pthread && DriverArgs.hasArg(options::OPT_pthread);
+  // '-pthread' cannot be used with '-mthread-model single'
+  if (HasPthread && HasThreadModel && ThreadModel == "single")
+    Driver.Diag(diag::err_drv_argument_not_allowed_with)
+        << "-pthread" << "-mthread-model single";
+}
+
 wasm::Linker::Linker(const ToolChain &TC)
     : GnuTool("wasm::Linker", "lld", TC) {}
 
@@ -123,6 +144,17 @@ void WebAssembly::addClangTargetOptions(const ArgList &DriverArgs,
   if (DriverArgs.hasFlag(clang::driver::options::OPT_fuse_init_array,
                          options::OPT_fno_use_init_array, true))
     CC1Args.push_back("-fuse-init-array");
+
+  // Either '-mthread-model posix' or '-pthread' sets '-target-feature
+  // +atomics'. We intentionally didn't create '-matomics' and set the atomics
+  // target feature here depending on the other two options.
+  bool Pthread = false;
+  StringRef ThreadModel = "";
+  parseThreadArgs(getDriver(), DriverArgs, Pthread, ThreadModel);
+  if (Pthread || ThreadModel != "single") {
+    CC1Args.push_back("-target-feature");
+    CC1Args.push_back("+atomics");
+  }
 }
 
 ToolChain::RuntimeLibType WebAssembly::GetDefaultRuntimeLibType() const {
@@ -180,12 +212,15 @@ void WebAssembly::AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
   }
 }
 
-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.
-  // When threading support is standardized and implemented in popular engines,
-  // this override should be removed.
-  return "single";
+std::string WebAssembly::getThreadModel(const ArgList &DriverArgs) const {
+  // The WebAssembly MVP does not yet support threads. We set this to "posix"
+  // when '-pthread' is set.
+  bool Pthread = false;
+  StringRef ThreadModel = "";
+  parseThreadArgs(getDriver(), DriverArgs, Pthread, ThreadModel, false);
+  if (Pthread)
+    return "posix";
+  return ThreadModel;
 }
 
 Tool *WebAssembly::buildLinker() const {

clang/lib/Driver/ToolChains/WebAssembly.h

@@ -64,7 +64,7 @@ class LLVM_LIBRARY_VISIBILITY WebAssembly final : public ToolChain {
       llvm::opt::ArgStringList &CC1Args) const override;
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
-  std::string getThreadModel() const override;
+  std::string getThreadModel(const llvm::opt::ArgList &) const override;
 
   const char *getDefaultLinker() const override { return "wasm-ld"; }
 

clang/test/Driver/wasm-toolchain.c

@@ -38,3 +38,16 @@
 
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-wasi-musl --sysroot=/foo %s 2>&1 | FileCheck -check-prefix=COMPILE %s
 // COMPILE: clang{{.*}}" "-cc1" {{.*}} "-internal-isystem" "/foo/include/wasm32-wasi-musl" "-internal-isystem" "/foo/include"
+
+// Thread-related command line tests.
+// - '-mthread-model' sets '-target-feature +matomics'
+// - '-phread' sets both '-target-featuer +atomics' and '-mthread-model posix'
+
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s -mthread-model posix 2>&1 | FileCheck -check-prefix=POSIX %s
+// POSIX: clang{{.*}}" "-cc1" {{.*}} "-target-feature" "+atomics"
+
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s -pthread 2>&1 | FileCheck -check-prefix=PTHREAD %s
+// PTHREAD: clang{{.*}}" "-cc1" {{.*}} "-mthread-model" "posix" {{.*}} "-target-feature" "+atomics"
+
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s -pthread -mthread-model single 2>&1 | FileCheck -check-prefix=THREAD_OPT_ERROR %s
+// THREAD_OPT_ERROR: invalid argument '-pthread' not allowed with '-mthread-model single'

clang/test/Preprocessor/wasm-target-features.c

@@ -52,11 +52,13 @@
 //
 // BULK-MEMORY:#define __wasm_bulk_memory__ 1{{$}}
 //
+// We don't use -matomics directly and '-mthread-model posix' sets the atomics
+// target feature.
 // RUN: %clang -E -dM %s -o - 2>&1 \
-// RUN:     -target wasm32-unknown-unknown -matomics \
+// RUN:     -target wasm32-unknown-unknown -mthread-model posix \
 // RUN:   | FileCheck %s -check-prefix=ATOMICS
 // RUN: %clang -E -dM %s -o - 2>&1 \
-// RUN:     -target wasm64-unknown-unknown -matomics \
+// RUN:     -target wasm64-unknown-unknown -mthread-model posix \
 // RUN:   | FileCheck %s -check-prefix=ATOMICS
 //
 // ATOMICS:#define __wasm_atomics__ 1{{$}}