[NFC] Be more lazy about looking up simulator SDKs on macs

[jasonmolenda]

Summary

This is a perf fix for when lldb on a mac is iterating through all of the Platforms looking for a good one, and the iOS/watchOS/tvOS simulators all call xcrun to find an SDK. If those SDKs are not installed, the xcruns can be quite expensive. The code today determines the SDK path before it knows if the Platform will create itself or not. When the SDKs are present, these xcrun calls are very inexpensive, but some people have different setups.

This patch passes the names of the SDKs into the central method that decides whether to create the Platform, and only searches for the SDK path via xcrun if this Platform is a match.

Adrian, I think you might have written this? If you'd like to review. Else I can ask around if anyone wants to take a look.

[aprantl]

Fair word of warning — i've broken more than one LLDB build in the past while messing with this code :-)

So you're basically sinking the calls to GetXcodeSDKPath into PlatformAppleSimulator. That looks safe & good to me!

lldb/source/Host/macosx/objcxx/HostInfoMacOSX.mm

       args.AppendArgument("/usr/bin/env");
       args.AppendArgument("DEVELOPER_DIR=" + developer_dir.str());
     }
     args.AppendArgument("/usr/bin/xcrun");
     args.AppendArgument("--show-sdk-path");
     args.AppendArgument("--sdk");
     args.AppendArgument(sdk);
 
+    Log *log = GetLog(LLDBLog::Host);
+    if (log) {
+      std::string cmdstr;
+      args.GetCommandString(cmdstr);
+      log->Printf("GetXcodeSDK() running shell cmd '%s'", cmdstr.c_str());
+    }
+
     int status = 0;
     int signo = 0;
     std::string output_str;
     lldb_private::Status error =
         Host::RunShellCommand(args, FileSpec(), &status, &signo, &output_str,
                               std::chrono::seconds(15));
 
     // Check that xcrun return something useful.

lldb/source/Plugins/Platform/MacOSX/PlatformAppleSimulator.h

public:
 
   static lldb::PlatformSP
   CreateInstance(const char *class_name, const char *description,
                  ConstString plugin_name,
                  llvm::SmallVector<llvm::Triple::ArchType, 4> supported_arch,
                  llvm::Triple::OSType preferred_os,
                  llvm::SmallVector<llvm::Triple::OSType, 4> supported_os,
                  llvm::SmallVector<llvm::StringRef, 4> supported_triples,
-                 llvm::StringRef sdk, XcodeSDK::Type sdk_type,
+                 std::string sdk_name_preferred, std::string sdk_name_secondary,
+                 XcodeSDK::Type sdk_type,
                  CoreSimulatorSupport::DeviceType::ProductFamilyID kind,
                  bool force, const ArchSpec *arch);
 
   virtual ~PlatformAppleSimulator();
 
   llvm::StringRef GetPluginName() override {
     return m_plugin_name.GetStringRef();
   }

lldb/source/Plugins/Platform/MacOSX/PlatformAppleSimulator.cpp

 std::vector<ArchSpec> PlatformAppleSimulator::GetSupportedArchitectures(
     const ArchSpec &process_host_arch) {
   std::vector<ArchSpec> result(m_supported_triples.size());
   llvm::transform(m_supported_triples, result.begin(),
                   [](llvm::StringRef triple) { return ArchSpec(triple); });
   return result;
 }
 
+static llvm::StringRef GetXcodeSDKDir(std::string preferred,
+                                      std::string secondary) {
+  llvm::StringRef sdk;
+  sdk = HostInfo::GetXcodeSDKPath(XcodeSDK(std::move(preferred)));
+  if (sdk.empty())
+    sdk = HostInfo::GetXcodeSDKPath(XcodeSDK(std::move(secondary)));
+  return sdk;
+}
+
 PlatformSP PlatformAppleSimulator::CreateInstance(
     const char *class_name, const char *description, ConstString plugin_name,
     llvm::SmallVector<llvm::Triple::ArchType, 4> supported_arch,
     llvm::Triple::OSType preferred_os,
     llvm::SmallVector<llvm::Triple::OSType, 4> supported_os,
     llvm::SmallVector<llvm::StringRef, 4> supported_triples,
-    llvm::StringRef sdk, lldb_private::XcodeSDK::Type sdk_type,
+    std::string sdk_name_preferred, std::string sdk_name_secondary,
+    lldb_private::XcodeSDK::Type sdk_type,
     CoreSimulatorSupport::DeviceType::ProductFamilyID kind, bool force,
     const ArchSpec *arch) {
   Log *log = GetLog(LLDBLog::Platform);
   if (log) {
     const char *arch_name;
     if (arch && arch->GetArchitectureName())
       arch_name = arch->GetArchitectureName();
     else

         else
           create = false;
       }
     }
   }
   if (create) {
     LLDB_LOGF(log, "%s::%s() creating platform", class_name, __FUNCTION__);
 
+    llvm::StringRef sdk =
+        GetXcodeSDKDir(sdk_name_preferred, sdk_name_secondary);
     return PlatformSP(new PlatformAppleSimulator(
         class_name, description, plugin_name, preferred_os, supported_triples,
         sdk, sdk_type, kind));
   }
 
   LLDB_LOGF(log, "%s::%s() aborting creation of platform", class_name,
             __FUNCTION__);
 

   // If the arch is known not to specify a simulator environment, skip creating
   // the simulator platform (we can create it later if there's a matching arch).
   // This avoids very slow xcrun queries for non-simulator archs (the slowness
   // is due to xcrun not caching negative queries (rdar://74882205)).
   return !force && arch && arch->IsValid() &&
          !arch->TripleEnvironmentWasSpecified();
 }
 
-static llvm::StringRef GetXcodeSDKDir(std::string preferred,
-                                      std::string secondary) {
-  llvm::StringRef sdk;
-  sdk = HostInfo::GetXcodeSDKPath(XcodeSDK(std::move(preferred)));
-  if (sdk.empty())
-    sdk = HostInfo::GetXcodeSDKPath(XcodeSDK(std::move(secondary)));
-  return sdk;
-}
-
 static const char *g_ios_plugin_name = "ios-simulator";
 static const char *g_ios_description = "iPhone simulator platform plug-in.";
 
 /// IPhone Simulator Plugin.
 struct PlatformiOSSimulator {
   static void Initialize() {
     PluginManager::RegisterPlugin(g_ios_plugin_name, g_ios_description,
                                   PlatformiOSSimulator::CreateInstance);
   }
 
   static void Terminate() {
     PluginManager::UnregisterPlugin(PlatformiOSSimulator::CreateInstance);
   }
 
   static PlatformSP CreateInstance(bool force, const ArchSpec *arch) {
     if (shouldSkipSimulatorPlatform(force, arch))
       return nullptr;
-    llvm::StringRef sdk;
-    sdk = HostInfo::GetXcodeSDKPath(XcodeSDK("iPhoneSimulator.Internal.sdk"));
-    if (sdk.empty())
-      sdk = HostInfo::GetXcodeSDKPath(XcodeSDK("iPhoneSimulator.sdk"));
 
     return PlatformAppleSimulator::CreateInstance(
         "PlatformiOSSimulator", g_ios_description,
         ConstString(g_ios_plugin_name),
         {llvm::Triple::aarch64, llvm::Triple::x86_64, llvm::Triple::x86},
         llvm::Triple::IOS,
         {// Deprecated, but still support Darwin for historical reasons.
          llvm::Triple::Darwin, llvm::Triple::MacOSX,
          // IOS is not used for simulator triples, but accept it just in
          // case.
          llvm::Triple::IOS},
         {
 #ifdef __APPLE__
 #if __arm64__
           "arm64e-apple-ios-simulator", "arm64-apple-ios-simulator",
               "x86_64-apple-ios-simulator", "x86_64h-apple-ios-simulator",
 #else
           "x86_64h-apple-ios-simulator", "x86_64-apple-ios-simulator",
               "i386-apple-ios-simulator",
 #endif
 #endif
         },
-        GetXcodeSDKDir("iPhoneSimulator.Internal.sdk", "iPhoneSimulator.sdk"),
+        "iPhoneSimulator.Internal.sdk", "iPhoneSimulator.sdk",
         XcodeSDK::Type::iPhoneSimulator,
         CoreSimulatorSupport::DeviceType::ProductFamilyID::iPhone, force, arch);
   }
 };
 
 static const char *g_tvos_plugin_name = "tvos-simulator";
 static const char *g_tvos_description = "tvOS simulator platform plug-in.";
 

 #if __arm64__
           "arm64e-apple-tvos-simulator", "arm64-apple-tvos-simulator",
               "x86_64h-apple-tvos-simulator", "x86_64-apple-tvos-simulator",
 #else
           "x86_64h-apple-tvos-simulator", "x86_64-apple-tvos-simulator",
 #endif
 #endif
         },
-        GetXcodeSDKDir("AppleTVSimulator.Internal.sdk", "AppleTVSimulator.sdk"),
+        "AppleTVSimulator.Internal.sdk", "AppleTVSimulator.sdk",
         XcodeSDK::Type::AppleTVSimulator,
         CoreSimulatorSupport::DeviceType::ProductFamilyID::appleTV, force,
         arch);
   }
 };
 
 
 static const char *g_watchos_plugin_name = "watchos-simulator";

 #if __arm64__
           "arm64e-apple-watchos-simulator", "arm64-apple-watchos-simulator",
 #else
           "x86_64-apple-watchos-simulator", "x86_64h-apple-watchos-simulator",
               "i386-apple-watchos-simulator",
 #endif
 #endif
         },
-        GetXcodeSDKDir("WatchSimulator.Internal.sdk", "WatchSimulator.sdk"),
+        "WatchSimulator.Internal.sdk", "WatchSimulator.sdk",
         XcodeSDK::Type::WatchSimulator,
         CoreSimulatorSupport::DeviceType::ProductFamilyID::appleWatch, force,
         arch);
   }
 };
 
 
 static unsigned g_initialize_count = 0;