[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

1 files changed, 6 insertions, 0 deletions

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; }