c2rust-transpile: handle builtin vector types (e.g. AArch64 SVE)

support for these was added in Clang/LLVM 11, so this handling is #ifdef'd on that

Author: fw-immunant

c2rust-ast-exporter/src/AstExporter.cpp

@@ -140,6 +140,25 @@ class TypeEncoder final : public TypeVisitor<TypeEncoder> {
         cbor_encoder_close_container(encoder, &local);
     }
 
+    DiagnosticBuilder getDiagBuilder(SourceLocation Loc,
+                                     DiagnosticsEngine::Level Lvl) {
+        auto &DiagEngine = Context->getDiagnostics();
+        // Prefix warnings with `c2rust`, so the user can distinguish
+        // our warning messages from those generated by clang itself.
+        const auto ID = DiagEngine.getCustomDiagID(Lvl, "c2rust: %0");
+        return DiagEngine.Report(Loc, ID);
+    }
+
+    void printWarning(std::string Message,
+                      SourceLocation S,
+                      SourceRange R = SourceRange()) {
+        auto DiagBuilder =
+            getDiagBuilder(S, DiagnosticsEngine::Warning);
+        DiagBuilder.AddString(Message);
+        DiagBuilder.AddSourceRange(
+            CharSourceRange::getCharRange(R));
+    }
+
   public:
     uintptr_t encodeQualType(QualType t) {
         auto s = t.split();
@@ -303,9 +322,36 @@ class TypeEncoder final : public TypeVisitor<TypeEncoder> {
         TypeTag tag;
         auto kind = T->getKind();
 
+        #if CLANG_VERSION_MAJOR >= 11
+        // Handle built-in vector types as if they're normal vector types
+        if (kind >= BuiltinType::SveInt8 && kind <= BuiltinType::SveBool) {
+            auto Info = Context->getBuiltinVectorTypeInfo(T);
+            auto t = Info.ElementType;
+            auto qt = encodeQualType(t);
+
+            encodeType(T, TagVectorType, [T, qt, Info](CborEncoder *local) {
+                cbor_encode_uint(local, qt);
+                cbor_encode_uint(local, Info.EC.getKnownMinValue() *
+                                            Info.NumVectors);
+            });
+
+            VisitQualType(t);
+            return;
+        }
+        #endif
+
         // clang-format off
         switch (kind) {
-        default:                      tag = TagTypeUnknown; break;
+        default: {
+            auto pol = clang::PrintingPolicy(Context->getLangOpts());
+            auto warning = std::string("Encountered unsupported BuiltinType kind ") +
+                           std::to_string((int)kind) + " for type " +
+                           T->getName(pol).str();
+            printWarning(warning, clang::FullSourceLoc());
+            tag = TagTypeUnknown;
+            break;
+        }
+
         case BuiltinType::BuiltinFn:  tag = TagBuiltinFn;   break;
         case BuiltinType::UInt128:    tag = TagUInt128;     break;
         case BuiltinType::Int128:     tag = TagInt128;      break;