[sanitizers] Use covering ObjectFormatType switches

[hubert.reinterpretcast]

Summary

This patch removes the default case from some switches on llvm::Triple::ObjectFormatType, and cases for the missing enumerators (UnknownObjectFormat, Wasm, and XCOFF) are then added.

For UnknownObjectFormat, the effect of the action for the default case is maintained; otherwise, where llvm_unreachable is called, report_fatal_error is used instead.

Where the default case returns a default value, report_fatal_error is used for XCOFF as a placeholder. For Wasm, the effect of the action for the default case in maintained.

The code is structured to avoid strongly implying that the Wasm case is present for any reason other than to make the switch cover all ObjectFormatType enumerator values.

[sfertile]

LGTM.

clang/lib/CodeGen/BackendUtil.cpp

static bool asanUseGlobalsGC(const Triple &T, const CodeGenOptions &CGOpts) {
   if (!CGOpts.SanitizeAddressGlobalsDeadStripping)
     return false;
   switch (T.getObjectFormat()) {
   case Triple::MachO:
   case Triple::COFF:
     return true;
   case Triple::ELF:
     return CGOpts.DataSections && !CGOpts.DisableIntegratedAS;
-  default:
-    return false;
+  case Triple::XCOFF:
+    llvm::report_fatal_error("ASan not implemented for XCOFF.");
+  case Triple::Wasm:
+  case Triple::UnknownObjectFormat:
+    break;
   }
+  return false;
 }
 
 static void addAddressSanitizerPasses(const PassManagerBuilder &Builder,
                                       legacy::PassManagerBase &PM) {
   const PassManagerBuilderWrapper &BuilderWrapper =
       static_cast<const PassManagerBuilderWrapper&>(Builder);
   const Triple &T = BuilderWrapper.getTargetTriple();
   const CodeGenOptions &CGOpts = BuilderWrapper.getCGOpts();

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

bool ModuleAddressSanitizer::ShouldUseMachOGlobalsSection() const {
   return false;
 }
 
 StringRef ModuleAddressSanitizer::getGlobalMetadataSection() const {
   switch (TargetTriple.getObjectFormat()) {
   case Triple::COFF:  return ".ASAN$GL";
   case Triple::ELF:   return "asan_globals";
   case Triple::MachO: return "__DATA,__asan_globals,regular";
-  default: break;
+  case Triple::Wasm:
+  case Triple::XCOFF:
+    report_fatal_error(
+        "ModuleAddressSanitizer not implemented for object file format.");
+  case Triple::UnknownObjectFormat:
+    break;
   }
   llvm_unreachable("unsupported object format");
 }
 
 void ModuleAddressSanitizer::initializeCallbacks(Module &M) {
   IRBuilder<> IRB(*C);
 
   // Declare our poisoning and unpoisoning functions.