[WebAssembly] Explicily disable comdat support for wasm output

For now at least.  We clearly need some kind of comdat or
linkonce_odr support for wasm but currently COMDAT is not
supported.

Disable COMDAT support in the same way we do the Mach-O.  This
also causes clang not to generated COMDATs.

Differential Revision: https://reviews.llvm.org/D39873

llvm-svn: 318123

llvm/include/llvm/ADT/Triple.h

@@ -661,7 +661,9 @@ public:
   }
 
   /// Tests wether the target supports comdat
-  bool supportsCOMDAT() const { return !isOSBinFormatMachO(); }
+  bool supportsCOMDAT() const {
+    return !isOSBinFormatMachO() && !isOSBinFormatWasm();
+  }
 
   /// @}
   /// @name Mutators

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -1825,10 +1825,10 @@ Expected<Value *> BitcodeReader::recordValue(SmallVectorImpl<uint64_t> &Record,
   auto *GO = dyn_cast<GlobalObject>(V);
   if (GO) {
     if (GO->getComdat() == reinterpret_cast<Comdat *>(1)) {
-      if (TT.isOSBinFormatMachO())
-        GO->setComdat(nullptr);
-      else
+      if (TT.supportsCOMDAT())
         GO->setComdat(TheModule->getOrInsertComdat(V->getName()));
+      else
+        GO->setComdat(nullptr);
     }
   }
   return V;

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -1233,21 +1233,21 @@ void TargetLoweringObjectFileCOFF::emitLinkerFlagsForGlobal(
 //                                  Wasm
 //===----------------------------------------------------------------------===//
 
-static const Comdat *getWasmComdat(const GlobalValue *GV) {
+static void checkWasmComdat(const GlobalValue *GV) {
   const Comdat *C = GV->getComdat();
   if (!C)
-    return nullptr;
+    return;
 
-  if (C->getSelectionKind() != Comdat::Any)
-    report_fatal_error("Wasm COMDATs only support SelectionKind::Any, '" +
-                       C->getName() + "' cannot be lowered.");
-
-  return C;
+  // TODO(sbc): At some point we may need COMDAT support but currently
+  // they are not supported.
+  report_fatal_error("WebAssembly doesn't support COMDATs, '" + C->getName() +
+                     "' cannot be lowered.");
 }
 
 MCSection *TargetLoweringObjectFileWasm::getExplicitSectionGlobal(
     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
   StringRef Name = GO->getSection();
+  checkWasmComdat(GO);
   return getContext().getWasmSection(Name, SectionKind::getData());
 }
 
@@ -1255,8 +1255,7 @@ static MCSectionWasm *selectWasmSectionForGlobal(
     MCContext &Ctx, const GlobalObject *GO, SectionKind Kind, Mangler &Mang,
     const TargetMachine &TM, bool EmitUniqueSection, unsigned *NextUniqueID) {
   StringRef Group = "";
-  if (getWasmComdat(GO))
-    llvm_unreachable("comdat not yet supported for wasm");
+  checkWasmComdat(GO);
 
   bool UniqueSectionNames = TM.getUniqueSectionNames();
   SmallString<128> Name = getSectionPrefixForGlobal(Kind);

llvm/test/CodeGen/WebAssembly/comdat.ll

@@ -0,0 +1,5 @@
+; RUN: not llc -mtriple wasm32-unknown-unknown-wasm %s 2>&1 | FileCheck %s
+
+$f = comdat any
+@f = global i32 0, comdat
+; CHECK: LLVM ERROR: WebAssembly doesn't support COMDATs, 'f' cannot be lowered.