[llvm-rtdyld] Avoid repeated hash lookups (NFC) (#130711)

Author: kazutakahirata

llvm/tools/llvm-rtdyld/llvm-rtdyld.cpp

@@ -929,15 +929,17 @@ static int linkAndVerify() {
                                        StringRef SymbolName,
                                        StringRef KindNameFilter)
       -> Expected<RuntimeDyldChecker::MemoryRegionInfo> {
-    if (!StubMap.count(StubContainer))
+    auto SMIt = StubMap.find(StubContainer);
+    if (SMIt == StubMap.end())
       return make_error<StringError>("Stub container not found: " +
                                          StubContainer,
                                      inconvertibleErrorCode());
-    if (!StubMap[StubContainer].count(SymbolName))
+    auto It = SMIt->second.find(SymbolName);
+    if (It == SMIt->second.end())
       return make_error<StringError>("Symbol name " + SymbolName +
                                          " in stub container " + StubContainer,
                                      inconvertibleErrorCode());
-    auto &SI = StubMap[StubContainer][SymbolName];
+    auto &SI = It->second;
     RuntimeDyldChecker::MemoryRegionInfo StubMemInfo;
     StubMemInfo.setTargetAddress(Dyld.getSectionLoadAddress(SI.SectionID) +
                                  SI.Offset);