[WebAssembly] Remove uses of ThreadModel

Summary:
In the clang UI, replaces -mthread-model posix with -matomics as the
source of truth on threading. In the backend, replaces
-thread-model=posix with the atomics target feature, which is now
collected on the WebAssemblyTargetMachine along with all other used
features. These collected features will also be used to emit the
target features section in the future.

The default configuration for the backend is thread-model=posix and no
atomics, which was previously an invalid configuration. This change
makes the default valid because the thread model is ignored.

A side effect of this change is that objects are never emitted with
passive segments. It will instead be up to the linker to decide
whether sections should be active or passive based on whether atomics
are used in the final link.

Reviewers: aheejin, sbc100, dschuff

Subscribers: mehdi_amini, jgravelle-google, hiraditya, sunfish, steven_wu, dexonsmith, rupprecht, jfb, jdoerfert, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D58742

llvm-svn: 355112

32 files changed, 129 insertions, 144 deletions

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index dd597550d2f..8a68e68a2d7 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -2160,6 +2160,8 @@ def msign_ext : Flag<["-"], "msign-ext">, Group<m_wasm_Features_Group>;
 def mno_sign_ext : Flag<["-"], "mno-sign-ext">, Group<m_wasm_Features_Group>;
 def mexception_handing : Flag<["-"], "mexception-handling">, Group<m_wasm_Features_Group>;
 def mno_exception_handing : Flag<["-"], "mno-exception-handling">, 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 mbulk_memory : Flag<["-"], "mbulk-memory">, Group<m_wasm_Features_Group>;
 def mno_bulk_memory : Flag<["-"], "mno-bulk-memory">, Group<m_wasm_Features_Group>;
 
diff --git a/clang/include/clang/Driver/ToolChain.h b/clang/include/clang/Driver/ToolChain.h
index e82675d3345..eec49ec3dde 100644
--- a/clang/include/clang/Driver/ToolChain.h
+++ b/clang/include/clang/Driver/ToolChain.h
@@ -453,9 +453,7 @@ public:
   virtual bool SupportsEmbeddedBitcode() const { return false; }
 
   /// getThreadModel() - Which thread model does this target use?
-  virtual std::string getThreadModel(const llvm::opt::ArgList &) const {
-    return "posix";
-  }
+  virtual std::string getThreadModel() const { return "posix"; }
 
   /// isThreadModelSupported() - Does this target support a thread model?
   virtual bool isThreadModelSupported(const StringRef Model) const;
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index b405390d44e..eb03e6e87cc 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/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(C.getArgs());
+    OS << "Thread model: " << TC.getThreadModel();
   OS << '\n';
 
   // Print out the install directory.
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index e7fb3fe403c..ff48360b666 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3830,7 +3830,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back(A->getValue());
   }
   else
-    CmdArgs.push_back(Args.MakeArgString(TC.getThreadModel(Args)));
+    CmdArgs.push_back(Args.MakeArgString(TC.getThreadModel()));
 
   Args.AddLastArg(CmdArgs, options::OPT_fveclib);
 
diff --git a/clang/lib/Driver/ToolChains/WebAssembly.cpp b/clang/lib/Driver/ToolChains/WebAssembly.cpp
index f076b528ce4..ce28d447ff2 100644
--- a/clang/lib/Driver/ToolChains/WebAssembly.cpp
+++ b/clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -20,27 +20,6 @@ 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) {}
 
@@ -145,15 +124,36 @@ void WebAssembly::addClangTargetOptions(const ArgList &DriverArgs,
                          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") {
+  // '-pthread' implies '-target-feature +atomics' and
+  // '-target-feature +bulk-memory'
+  if (DriverArgs.hasFlag(options::OPT_pthread, options::OPT_no_pthread,
+                         false)) {
+    if (DriverArgs.hasFlag(options::OPT_mno_atomics, options::OPT_matomics,
+                           false))
+      getDriver().Diag(diag::err_drv_argument_not_allowed_with)
+          << "-pthread"
+          << "-mno-atomics";
+    if (DriverArgs.hasFlag(options::OPT_mno_bulk_memory,
+                           options::OPT_mbulk_memory, false))
+      getDriver().Diag(diag::err_drv_argument_not_allowed_with)
+          << "-pthread"
+          << "-mno-bulk-memory";
     CC1Args.push_back("-target-feature");
     CC1Args.push_back("+atomics");
+    CC1Args.push_back("-target-feature");
+    CC1Args.push_back("+bulk-memory");
+  }
+
+  // '-matomics' implies '-mbulk-memory'
+  if (DriverArgs.hasFlag(options::OPT_matomics, options::OPT_mno_atomics,
+                         false)) {
+    if (DriverArgs.hasFlag(options::OPT_mno_bulk_memory,
+                           options::OPT_mbulk_memory, false))
+      getDriver().Diag(diag::err_drv_argument_not_allowed_with)
+          << "-matomics"
+          << "-mno-bulk-memory";
+    CC1Args.push_back("-target-feature");
+    CC1Args.push_back("+bulk-memory");
   }
 }
 
@@ -212,17 +212,6 @@ void WebAssembly::AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
   }
 }
 
-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 {
   return new tools::wasm::Linker(*this);
 }
diff --git a/clang/lib/Driver/ToolChains/WebAssembly.h b/clang/lib/Driver/ToolChains/WebAssembly.h
index 6ededd84ec6..2d9210ac04c 100644
--- a/clang/lib/Driver/ToolChains/WebAssembly.h
+++ b/clang/lib/Driver/ToolChains/WebAssembly.h
@@ -64,7 +64,6 @@ private:
       llvm::opt::ArgStringList &CC1Args) const override;
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
-  std::string getThreadModel(const llvm::opt::ArgList &) const override;
 
   const char *getDefaultLinker() const override { return "wasm-ld"; }
 
diff --git a/clang/test/Driver/wasm-toolchain.c b/clang/test/Driver/wasm-toolchain.c
index 22867117ffd..bdef316c85c 100644
--- a/clang/test/Driver/wasm-toolchain.c
+++ b/clang/test/Driver/wasm-toolchain.c
@@ -40,14 +40,19 @@
 // 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"
 
+// '-pthread' sets '-target-feature +atomics' and '-target-feature +bulk-memory'
 // 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"
+// PTHREAD: clang{{.*}}" "-cc1" {{.*}} "-target-feature" "+atomics" "-target-feature" "+bulk-memory"
+
+// '-pthread' not allowed with '-mno-atomics'
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s -pthread -mno-atomics 2>&1 | FileCheck -check-prefix=PTHREAD_NO_ATOMICS %s
+// PTHREAD_NO_ATOMICS: invalid argument '-pthread' not allowed with '-mno-atomics'
+
+// '-pthread' not allowed with '-mno-bulk-memory'
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s -pthread -mno-bulk-memory 2>&1 | FileCheck -check-prefix=PTHREAD_NO_BULKMEM %s
+// PTHREAD_NO_BULKMEM: invalid argument '-pthread' not allowed with '-mno-bulk-memory'
 
-// 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'
+// '-matomics' not allowed with '-mno-bulk-memory'
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s -matomics -mno-bulk-memory 2>&1 | FileCheck -check-prefix=ATOMICS_NO_BULKMEM %s
+// ATOMICS_NO_BULKMEM: invalid argument '-matomics' not allowed with '-mno-bulk-memory'
diff --git a/clang/test/Preprocessor/wasm-target-features.c b/clang/test/Preprocessor/wasm-target-features.c
index 3ab22500c15..80e299247c7 100644
--- a/clang/test/Preprocessor/wasm-target-features.c
+++ b/clang/test/Preprocessor/wasm-target-features.c
@@ -6,7 +6,7 @@
 // RUN:   | FileCheck %s -check-prefix=SIMD128
 //
 // SIMD128:#define __wasm_simd128__ 1{{$}}
-//
+
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -munimplemented-simd128 \
 // RUN:   | FileCheck %s -check-prefix=SIMD128-UNIMPLEMENTED
@@ -15,7 +15,7 @@
 // RUN:   | FileCheck %s -check-prefix=SIMD128-UNIMPLEMENTED
 //
 // SIMD128-UNIMPLEMENTED:#define __wasm_unimplemented_simd128__ 1{{$}}
-//
+
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mnontrapping-fptoint \
 // RUN:   | FileCheck %s -check-prefix=NONTRAPPING-FPTOINT
@@ -24,7 +24,7 @@
 // RUN:   | FileCheck %s -check-prefix=NONTRAPPING-FPTOINT
 //
 // NONTRAPPING-FPTOINT:#define __wasm_nontrapping_fptoint__ 1{{$}}
-//
+
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -msign-ext \
 // RUN:   | FileCheck %s -check-prefix=SIGN-EXT
@@ -33,7 +33,7 @@
 // RUN:   | FileCheck %s -check-prefix=SIGN-EXT
 //
 // SIGN-EXT:#define __wasm_sign_ext__ 1{{$}}
-//
+
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mexception-handling \
 // RUN:   | FileCheck %s -check-prefix=EXCEPTION-HANDLING
@@ -42,7 +42,7 @@
 // RUN:   | FileCheck %s -check-prefix=EXCEPTION-HANDLING
 //
 // EXCEPTION-HANDLING:#define __wasm_exception_handling__ 1{{$}}
-//
+
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mbulk-memory \
 // RUN:   | FileCheck %s -check-prefix=BULK-MEMORY
@@ -51,18 +51,27 @@
 // RUN:   | FileCheck %s -check-prefix=BULK-MEMORY
 //
 // BULK-MEMORY:#define __wasm_bulk_memory__ 1{{$}}
-//
-// 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 -mthread-model posix \
+// RUN:     -target wasm32-unknown-unknown -matomics \
 // RUN:   | FileCheck %s -check-prefix=ATOMICS
 // RUN: %clang -E -dM %s -o - 2>&1 \
-// RUN:     -target wasm64-unknown-unknown -mthread-model posix \
+// RUN:     -target wasm64-unknown-unknown -matomics \
 // RUN:   | FileCheck %s -check-prefix=ATOMICS
 //
-// ATOMICS:#define __wasm_atomics__ 1{{$}}
+// ATOMICS-DAG:#define __wasm_atomics__ 1{{$}}
+// ATOMICS-DAG:#define __wasm_bulk_memory__ 1{{$}}
+
+// RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm32-unknown-unknown -pthread \
+// RUN:   | FileCheck %s -check-prefix=PTHREAD
+// RUN: %clang -E -dM %s -o - 2>&1 \
+// RUN:     -target wasm64-unknown-unknown -pthread \
+// RUN:   | FileCheck %s -check-prefix=PTHREAD
 //
+// PTHREAD-DAG:#define __wasm_atomics__ 1{{$}}
+// PTHREAD-DAG:#define __wasm_bulk_memory__ 1{{$}}
+
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mcpu=mvp \
 // RUN:   | FileCheck %s -check-prefix=MVP
@@ -77,7 +86,7 @@
 // MVP-NOT:#define __wasm_exception_handling__
 // MVP-NOT:#define __wasm_bulk_memory__
 // MVP-NOT:#define __wasm_atomics__
-//
+
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mcpu=bleeding-edge \
 // RUN:   | FileCheck %s -check-prefix=BLEEDING-EDGE
@@ -90,7 +99,7 @@
 // BLEEDING-EDGE-DAG:#define __wasm_simd128__ 1{{$}}
 // BLEEDING-EDGE-DAG:#define __wasm_atomics__ 1{{$}}
 // BLEEDING-EDGE-NOT:#define __wasm_unimplemented_simd128__ 1{{$}}
-//
+
 // RUN: %clang -E -dM %s -o - 2>&1 \
 // RUN:     -target wasm32-unknown-unknown -mcpu=bleeding-edge -mno-simd128 \
 // RUN:   | FileCheck %s -check-prefix=BLEEDING-EDGE-NO-SIMD128
diff --git a/lld/test/wasm/init-fini.ll b/lld/test/wasm/init-fini.ll
index f0d6092867b..b17020b177c 100644
--- a/lld/test/wasm/init-fini.ll
+++ b/lld/test/wasm/init-fini.ll
@@ -1,5 +1,5 @@
-; RUN: llc -filetype=obj -thread-model=single -o %t.o %s
-; RUN: llc -filetype=obj -thread-model=single %S/Inputs/global-ctor-dtor.ll -o %t.global-ctor-dtor.o
+; RUN: llc -filetype=obj -o %t.o %s
+; RUN: llc -filetype=obj %S/Inputs/global-ctor-dtor.ll -o %t.global-ctor-dtor.o
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/lld/test/wasm/lto/atomics.ll b/lld/test/wasm/lto/atomics.ll
index a5a82ae2a5f..00340f12b2b 100644
--- a/lld/test/wasm/lto/atomics.ll
+++ b/lld/test/wasm/lto/atomics.ll
@@ -1,7 +1,8 @@
 ; RUN: llvm-as %s -o %t.o
 ; RUN: wasm-ld %t.o -o %t.wasm -lto-O0
-; Atomic operations with fail to compile if the ThreadModel is not
-; correctly set to Single (i.e. if atomics are not lowered to regular ops).
+
+; Atomic operations will not fail to compile if atomics are not
+; enabled because LLVM atomics will be lowered to regular ops.
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown-wasm"
diff --git a/lld/wasm/LTO.cpp b/lld/wasm/LTO.cpp
index 19b23d50c50..2b49bac5cf2 100644
--- a/lld/wasm/LTO.cpp
+++ b/lld/wasm/LTO.cpp
@@ -47,9 +47,6 @@ static std::unique_ptr<lto::LTO> createLTO() {
   C.Options.FunctionSections = true;
   C.Options.DataSections = true;
 
-  // Wasm currently only supports ThreadModel::Single
-  C.Options.ThreadModel = ThreadModel::Single;
-
   C.DisableVerify = Config->DisableVerify;
   C.DiagHandler = diagnosticHandler;
   C.OptLevel = Config->LTOO;
diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index c50c6476ec5..436076f33b9 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -1697,9 +1697,6 @@ MCSection *TargetLoweringObjectFileWasm::getExplicitSectionGlobal(
       getContext().getWasmSection(Name, Kind, Group,
                                   MCContext::GenericSectionID);
 
-  if (TM.Options.ThreadModel != ThreadModel::Single)
-    Section->setPassive();
-
   return Section;
 }
 
@@ -1730,11 +1727,7 @@ static MCSectionWasm *selectWasmSectionForGlobal(
     (*NextUniqueID)++;
   }
 
-  MCSectionWasm* Section = Ctx.getWasmSection(Name, Kind, Group, UniqueID);
-  if (Section->isWasmData() && TM.Options.ThreadModel != ThreadModel::Single)
-    Section->setPassive();
-
-  return Section;
+  return Ctx.getWasmSection(Name, Kind, Group, UniqueID);
 }
 
 MCSection *TargetLoweringObjectFileWasm::SelectSectionForGlobal(
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index 8e8b4878c52..768ab7a099c 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -115,6 +115,10 @@ WebAssemblyTargetMachine::WebAssemblyTargetMachine(
 
   initAsmInfo();
 
+  // Create a subtarget using the unmodified target machine features to
+  // initialize the used feature set with explicitly enabled features.
+  getSubtargetImpl(getTargetCPU(), getTargetFeatureString());
+
   // Note that we don't use setRequiresStructuredCFG(true). It disables
   // optimizations than we're ok with, and want, such as critical edge
   // splitting and tail merging.
@@ -123,6 +127,17 @@ WebAssemblyTargetMachine::WebAssemblyTargetMachine(
 WebAssemblyTargetMachine::~WebAssemblyTargetMachine() = default; // anchor.
 
 const WebAssemblySubtarget *
+WebAssemblyTargetMachine::getSubtargetImpl(std::string CPU,
+                                           std::string FS) const {
+  auto &I = SubtargetMap[CPU + FS];
+  if (!I) {
+    I = llvm::make_unique<WebAssemblySubtarget>(TargetTriple, CPU, FS, *this);
+    UsedFeatures |= I->getFeatureBits();
+  }
+  return I.get();
+}
+
+const WebAssemblySubtarget *
 WebAssemblyTargetMachine::getSubtargetImpl(const Function &F) const {
   Attribute CPUAttr = F.getFnAttribute("target-cpu");
   Attribute FSAttr = F.getFnAttribute("target-features");
@@ -134,15 +149,12 @@ WebAssemblyTargetMachine::getSubtargetImpl(const Function &F) const {
                        ? FSAttr.getValueAsString().str()
                        : TargetFS;
 
-  auto &I = SubtargetMap[CPU + FS];
-  if (!I) {
-    // This needs to be done before we create a new subtarget since any
-    // creation will depend on the TM and the code generation flags on the
-    // function that reside in TargetOptions.
-    resetTargetOptions(F);
-    I = llvm::make_unique<WebAssemblySubtarget>(TargetTriple, CPU, FS, *this);
-  }
-  return I.get();
+  // This needs to be done before we create a new subtarget since any
+  // creation will depend on the TM and the code generation flags on the
+  // function that reside in TargetOptions.
+  resetTargetOptions(F);
+
+  return getSubtargetImpl(CPU, FS);
 }
 
 namespace {
@@ -202,14 +214,15 @@ FunctionPass *WebAssemblyPassConfig::createTargetRegisterAllocator(bool) {
 //===----------------------------------------------------------------------===//
 
 void WebAssemblyPassConfig::addIRPasses() {
-  if (TM->Options.ThreadModel == ThreadModel::Single) {
-    // In "single" mode, atomics get lowered to non-atomics.
-    addPass(createLowerAtomicPass());
-    addPass(new StripThreadLocal());
-  } else {
+  if (static_cast<WebAssemblyTargetMachine *>(TM)
+          ->getUsedFeatures()[WebAssembly::FeatureAtomics]) {
     // Expand some atomic operations. WebAssemblyTargetLowering has hooks which
     // control specifically what gets lowered.
     addPass(createAtomicExpandPass());
+  } else {
+    // If atomics are not enabled, they get lowered to non-atomics.
+    addPass(createLowerAtomicPass());
+    addPass(new StripThreadLocal());
   }
 
   // Add signatures to prototype-less function declarations
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.h b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.h
index e13ad7d4eac..0630797fe81 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.h
@@ -23,6 +23,7 @@ namespace llvm {
 class WebAssemblyTargetMachine final : public LLVMTargetMachine {
   std::unique_ptr<TargetLoweringObjectFile> TLOF;
   mutable StringMap<std::unique_ptr<WebAssemblySubtarget>> SubtargetMap;
+  mutable FeatureBitset UsedFeatures;
 
 public:
   WebAssemblyTargetMachine(const Target &T, const Triple &TT, StringRef CPU,
@@ -32,6 +33,9 @@ public:
                            bool JIT);
 
   ~WebAssemblyTargetMachine() override;
+
+  const WebAssemblySubtarget *getSubtargetImpl(std::string CPU,
+                                               std::string FS) const;
   const WebAssemblySubtarget *
   getSubtargetImpl(const Function &F) const override;
 
@@ -42,6 +46,8 @@ public:
     return TLOF.get();
   }
 
+  FeatureBitset getUsedFeatures() const { return UsedFeatures; }
+
   TargetTransformInfo getTargetTransformInfo(const Function &F) override;
 
   bool usesPhysRegsForPEI() const override { return false; }
diff --git a/llvm/test/CodeGen/WebAssembly/atomic-mem-consistency.ll b/llvm/test/CodeGen/WebAssembly/atomic-mem-consistency.ll
index 3a714370d84..c2cb02acc1e 100644
--- a/llvm/test/CodeGen/WebAssembly/atomic-mem-consistency.ll
+++ b/llvm/test/CodeGen/WebAssembly/atomic-mem-consistency.ll
@@ -1,4 +1,4 @@
-; RUN: not llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt
 ; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -mattr=+atomics,+sign-ext | FileCheck %s
 
 ; Currently all wasm atomic memory access instructions are sequentially
diff --git a/llvm/test/CodeGen/WebAssembly/atomic-rmw.ll b/llvm/test/CodeGen/WebAssembly/atomic-rmw.ll
index 27b3be09943..34f505b7d6b 100644
--- a/llvm/test/CodeGen/WebAssembly/atomic-rmw.ll
+++ b/llvm/test/CodeGen/WebAssembly/atomic-rmw.ll
@@ -1,4 +1,4 @@
-; RUN: not llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers
 ; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -mattr=+atomics,+sign-ext | FileCheck %s
 
 ; Test atomic RMW (read-modify-write) instructions are assembled properly.
diff --git a/llvm/test/CodeGen/WebAssembly/global.ll b/llvm/test/CodeGen/WebAssembly/global.ll
index d341ebc8f36..12f4db43f38 100644
--- a/llvm/test/CodeGen/WebAssembly/global.ll
+++ b/llvm/test/CodeGen/WebAssembly/global.ll
@@ -1,5 +1,5 @@
-; RUN: llc < %s -thread-model=single -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s --check-prefixes=CHECK,SINGLE
-; RUN: llc < %s -thread-model=posix -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s --check-prefixes=CHECK,THREADS
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -mattr=-atomics | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -mattr=+atomics | FileCheck %s
 
 ; Test that globals assemble as expected.
 
@@ -192,8 +192,7 @@ define i8* @call_memcpy(i8* %p, i8* nocapture readonly %q, i32 %n) {
 
 ; Constant global.
 ; CHECK: .type    rom,@object{{$}}
-; SINGLE: .section .rodata.rom,""
-; THREADS: .section .rodata.rom,"passive"
+; CHECK: .section .rodata.rom,""
 ; CHECK: .globl   rom{{$}}
 ; CHECK: .p2align   4{{$}}
 ; CHECK: rom:
@@ -206,8 +205,7 @@ define i8* @call_memcpy(i8* %p, i8* nocapture readonly %q, i32 %n) {
 ; CHECK-NEXT: .skip       8
 ; CHECK-NEXT: .size       array, 8
 ; CHECK: .type       pointer_to_array,@object
-; SINGLE-NEXT: .section    .rodata.pointer_to_array,""
-; THREADS-NEXT: .section    .rodata.pointer_to_array,"passive"
+; CHECK-NEXT: .section    .rodata.pointer_to_array,""
 ; CHECK-NEXT: .globl      pointer_to_array
 ; CHECK-NEXT: .p2align      2
 ; CHECK-NEXT: pointer_to_array:
diff --git a/llvm/test/CodeGen/WebAssembly/tls.ll b/llvm/test/CodeGen/WebAssembly/tls.ll
index 6843aa0f9be..21e84f9fa97 100644
--- a/llvm/test/CodeGen/WebAssembly/tls.ll
+++ b/llvm/test/CodeGen/WebAssembly/tls.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -thread-model=single | FileCheck --check-prefix=SINGLE %s
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck --check-prefix=SINGLE %s
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/CodeGen/WebAssembly/vtable.ll b/llvm/test/CodeGen/WebAssembly/vtable.ll
index 5a6d89d4e54..6a0d902254d 100644
--- a/llvm/test/CodeGen/WebAssembly/vtable.ll
+++ b/llvm/test/CodeGen/WebAssembly/vtable.ll
@@ -1,6 +1,6 @@
-; RUN: llc < %s -asm-verbose=false -thread-model=single -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s --check-prefix=TYPEINFONAME
-; RUN: llc < %s -asm-verbose=false -thread-model=single -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s --check-prefix=VTABLE
-; RUN: llc < %s -asm-verbose=false -thread-model=single -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s --check-prefix=TYPEINFO
+; RUN: llc < %s -asm-verbose=false -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s --check-prefix=TYPEINFONAME
+; RUN: llc < %s -asm-verbose=false -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s --check-prefix=VTABLE
+; RUN: llc < %s -asm-verbose=false -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s --check-prefix=TYPEINFO
 
 ; Test that simple vtables assemble as expected.
 ;
diff --git a/llvm/test/MC/WebAssembly/bss.ll b/llvm/test/MC/WebAssembly/bss.ll
index a274982ed5b..36785caa3ba 100644
--- a/llvm/test/MC/WebAssembly/bss.ll
+++ b/llvm/test/MC/WebAssembly/bss.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single %s -o - | obj2yaml | FileCheck %s
+; RUN: llc -filetype=obj %s -o - | obj2yaml | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/MC/WebAssembly/comdat.ll b/llvm/test/MC/WebAssembly/comdat.ll
index 9b1ac501dbf..95b77b9da61 100644
--- a/llvm/test/MC/WebAssembly/comdat.ll
+++ b/llvm/test/MC/WebAssembly/comdat.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single %s -o - | obj2yaml | FileCheck %s
+; RUN: llc -filetype=obj %s -o - | obj2yaml | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/MC/WebAssembly/debug-info.ll b/llvm/test/MC/WebAssembly/debug-info.ll
index 374f5b3528b..fe4a4cf6983 100644
--- a/llvm/test/MC/WebAssembly/debug-info.ll
+++ b/llvm/test/MC/WebAssembly/debug-info.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single %s -o - | llvm-readobj -r -s -symbols | FileCheck %s
+; RUN: llc -filetype=obj %s -o - | llvm-readobj -r -s -symbols | FileCheck %s
 
 ; CHECK: Format: WASM
 ; CHECK-NEXT:Arch: wasm32
diff --git a/llvm/test/MC/WebAssembly/explicit-sections.ll b/llvm/test/MC/WebAssembly/explicit-sections.ll
index 7fa6d4b6017..f6e9cae2868 100644
--- a/llvm/test/MC/WebAssembly/explicit-sections.ll
+++ b/llvm/test/MC/WebAssembly/explicit-sections.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single %s -o - | obj2yaml | FileCheck %s
+; RUN: llc -filetype=obj %s -o - | obj2yaml | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/MC/WebAssembly/external-data.ll b/llvm/test/MC/WebAssembly/external-data.ll
index 7598c920903..c1ebca69c37 100644
--- a/llvm/test/MC/WebAssembly/external-data.ll
+++ b/llvm/test/MC/WebAssembly/external-data.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single %s -o - | obj2yaml | FileCheck %s
+; RUN: llc -filetype=obj %s -o - | obj2yaml | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/MC/WebAssembly/external-func-address.ll b/llvm/test/MC/WebAssembly/external-func-address.ll
index 7ad4faa2701..95e679ab65d 100644
--- a/llvm/test/MC/WebAssembly/external-func-address.ll
+++ b/llvm/test/MC/WebAssembly/external-func-address.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single %s -o - | obj2yaml | FileCheck %s
+; RUN: llc -filetype=obj %s -o - | obj2yaml | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/MC/WebAssembly/global-ctor-dtor.ll b/llvm/test/MC/WebAssembly/global-ctor-dtor.ll
index 1405803dd8f..d7e9bc9676b 100644
--- a/llvm/test/MC/WebAssembly/global-ctor-dtor.ll
+++ b/llvm/test/MC/WebAssembly/global-ctor-dtor.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single %s -o - | obj2yaml | FileCheck %s
+; RUN: llc -filetype=obj %s -o - | obj2yaml | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/MC/WebAssembly/init-flags.ll b/llvm/test/MC/WebAssembly/init-flags.ll
deleted file mode 100644
index a5d2662436e..00000000000
--- a/llvm/test/MC/WebAssembly/init-flags.ll
+++ /dev/null
@@ -1,25 +0,0 @@
-; RUN: llc -filetype=obj %s -thread-model=single -o - | obj2yaml | FileCheck %s --check-prefix=SINGLE
-; RUN: llc -filetype=obj %s -thread-model=posix -o - | obj2yaml | FileCheck %s --check-prefix=THREADS
-
-; Test that setting thread-model=posix causes data segments to be
-; emitted as passive segments (i.e. have InitFlags set to 1).
-
-target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
-target triple = "wasm32-unknown-unknown"
-
-@str = private unnamed_addr constant [7 x i8] c"Hello!\00", align 1
-
-; SINGLE:       - Type:            DATA
-; SINGLE-NEXT:    Segments:
-; SINGLE-NEXT:      - SectionOffset:   6
-; SINGLE-NEXT:        InitFlags:       0
-; SINGLE-NEXT:        Offset:
-; SINGLE-NEXT:          Opcode:          I32_CONST
-; SINGLE-NEXT:          Value:           0
-; SINGLE-NEXT:        Content:         48656C6C6F2100
-
-; THREADS:       - Type:            DATA
-; THREADS-NEXT:    Segments:
-; THREADS-NEXT:      - SectionOffset:   3
-; THREADS-NEXT:        InitFlags:       1
-; THREADS-NEXT:        Content:         48656C6C6F2100
diff --git a/llvm/test/MC/WebAssembly/reloc-data.ll b/llvm/test/MC/WebAssembly/reloc-data.ll
index c812939711f..2c4b206fe9f 100644
--- a/llvm/test/MC/WebAssembly/reloc-data.ll
+++ b/llvm/test/MC/WebAssembly/reloc-data.ll
@@ -1,4 +1,4 @@
-; RUN: llc -O0 -filetype=obj -thread-model=single %s -o - | llvm-readobj -r -expand-relocs | FileCheck %s
+; RUN: llc -O0 -filetype=obj %s -o - | llvm-readobj -r -expand-relocs | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/MC/WebAssembly/unnamed-data.ll b/llvm/test/MC/WebAssembly/unnamed-data.ll
index 2eb30c71f4a..3b3b414dbf7 100644
--- a/llvm/test/MC/WebAssembly/unnamed-data.ll
+++ b/llvm/test/MC/WebAssembly/unnamed-data.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single %s -o - | obj2yaml | FileCheck %s
+; RUN: llc -filetype=obj %s -o - | obj2yaml | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/MC/WebAssembly/weak-alias.ll b/llvm/test/MC/WebAssembly/weak-alias.ll
index fe8112ddacb..7abdc79b569 100644
--- a/llvm/test/MC/WebAssembly/weak-alias.ll
+++ b/llvm/test/MC/WebAssembly/weak-alias.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single -wasm-keep-registers %s -o %t.o
+; RUN: llc -filetype=obj -wasm-keep-registers %s -o %t.o
 ; RUN: obj2yaml %t.o | FileCheck %s
 ; RUN: llvm-objdump -t %t.o | FileCheck --check-prefix=CHECK-SYMS %s
 
diff --git a/llvm/test/tools/llvm-nm/wasm/local-symbols.ll b/llvm/test/tools/llvm-nm/wasm/local-symbols.ll
index cc64f2e7f47..f7c0e837cc9 100644
--- a/llvm/test/tools/llvm-nm/wasm/local-symbols.ll
+++ b/llvm/test/tools/llvm-nm/wasm/local-symbols.ll
@@ -1,4 +1,4 @@
-; RUN: llc -filetype=obj -thread-model=single -mtriple=wasm32-unknown-unknown -o %t.o %s
+; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown -o %t.o %s
 ; RUN: llvm-nm %t.o | FileCheck %s
 
 @foo = internal global i32 1, align 4
diff --git a/llvm/test/tools/llvm-objdump/WebAssembly/relocations.test b/llvm/test/tools/llvm-objdump/WebAssembly/relocations.test
index d86e9392651..acf276e7ba7 100644
--- a/llvm/test/tools/llvm-objdump/WebAssembly/relocations.test
+++ b/llvm/test/tools/llvm-objdump/WebAssembly/relocations.test
@@ -1,4 +1,4 @@
-; RUN: llc -thread-model=single -mtriple=wasm32-unknown-unknown -filetype=obj %s -o - | llvm-objdump -r - | FileCheck %s
+; RUN: llc -mtriple=wasm32-unknown-unknown -filetype=obj %s -o - | llvm-objdump -r - | FileCheck %s
 
 @foo = external global i32, align 4
 @bar = global i32* @foo, align 4