[ORC] Fail early in ExecutionSession::registerJITDispatchHandlers.

Check that we're not reusing any handler tag addresses before installing any
handlers. This ensures that either all of the handlers are installed*, or none
of them are, simplifying error recovery.

* Ignoring handlers whose tags couldn't be resolved at all: these were never
installed.

Author: lhames

llvm/lib/ExecutionEngine/Orc/Core.cpp

@@ -1878,31 +1878,39 @@ ExecutionSession::lookup(ArrayRef<JITDylib *> SearchOrder, StringRef Name,
 Error ExecutionSession::registerJITDispatchHandlers(
     JITDylib &JD, JITDispatchHandlerAssociationMap WFs) {
 
-  auto TagAddrs = lookup({{&JD, JITDylibLookupFlags::MatchAllSymbols}},
-                         SymbolLookupSet::fromMapKeys(
-                             WFs, SymbolLookupFlags::WeaklyReferencedSymbol));
-  if (!TagAddrs)
-    return TagAddrs.takeError();
+  auto TagSyms = lookup({{&JD, JITDylibLookupFlags::MatchAllSymbols}},
+                        SymbolLookupSet::fromMapKeys(
+                            WFs, SymbolLookupFlags::WeaklyReferencedSymbol));
+  if (!TagSyms)
+    return TagSyms.takeError();
 
   // Associate tag addresses with implementations.
   std::lock_guard<std::mutex> Lock(JITDispatchHandlersMutex);
-  for (auto &KV : *TagAddrs) {
-    auto TagAddr = KV.second.getAddress();
+
+  // Check that no tags are being overwritten.
+  for (auto &[TagName, TagSym] : *TagSyms) {
+    auto TagAddr = TagSym.getAddress();
     if (JITDispatchHandlers.count(TagAddr))
-      return make_error<StringError>("Tag " + formatv("{0:x16}", TagAddr) +
-                                         " (for " + *KV.first +
+      return make_error<StringError>("Tag " + formatv("{0:x}", TagAddr) +
+                                         " (for " + *TagName +
                                          ") already registered",
                                      inconvertibleErrorCode());
-    auto I = WFs.find(KV.first);
+  }
+
+  // At this point we're guaranteed to succeed. Install the handlers.
+  for (auto &[TagName, TagSym] : *TagSyms) {
+    auto TagAddr = TagSym.getAddress();
+    auto I = WFs.find(TagName);
     assert(I != WFs.end() && I->second &&
            "JITDispatchHandler implementation missing");
-    JITDispatchHandlers[KV.second.getAddress()] =
+    JITDispatchHandlers[TagAddr] =
         std::make_shared<JITDispatchHandlerFunction>(std::move(I->second));
     LLVM_DEBUG({
-      dbgs() << "Associated function tag \"" << *KV.first << "\" ("
-             << formatv("{0:x}", KV.second.getAddress()) << ") with handler\n";
+      dbgs() << "Associated function tag \"" << *TagName << "\" ("
+             << formatv("{0:x}", TagAddr) << ") with handler\n";
     });
   }
+
   return Error::success();
 }