Don't search for sim SDK path until we know we need it

When iterating over all Platforms looking for the best one, on a Mac the
Simulator platforms (iOS, tvOS, watchOS) will first find their SDK
directory by calling xcrun, then decide if they should activate or not.
When that SDK is absent, the call to xcrun to find it can be very slow.
This patch delays that directory search until we know we're activating
this platform, so non-simulator environments don't pay a perf cost ever
time they go through the list of platforms.

Differential Revision: https://reviews.llvm.org/D122373
rdar://87960090

Author: jasonmolenda

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

@@ -379,6 +379,13 @@ static void ParseOSVersion(llvm::VersionTuple &version, NSString *Key) {
     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/source/Plugins/Platform/MacOSX/PlatformAppleSimulator.cpp

@@ -274,13 +274,23 @@ std::vector<ArchSpec> PlatformAppleSimulator::GetSupportedArchitectures(
   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);
@@ -338,6 +348,8 @@ PlatformSP PlatformAppleSimulator::CreateInstance(
   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));
@@ -514,15 +526,6 @@ static bool shouldSkipSimulatorPlatform(bool force, const ArchSpec *arch) {
          !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.";
 
@@ -540,10 +543,6 @@ struct PlatformiOSSimulator {
   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,
@@ -566,7 +565,7 @@ struct PlatformiOSSimulator {
 #endif
 #endif
         },
-        GetXcodeSDKDir("iPhoneSimulator.Internal.sdk", "iPhoneSimulator.sdk"),
+        "iPhoneSimulator.Internal.sdk", "iPhoneSimulator.sdk",
         XcodeSDK::Type::iPhoneSimulator,
         CoreSimulatorSupport::DeviceType::ProductFamilyID::iPhone, force, arch);
   }
@@ -604,7 +603,7 @@ struct PlatformAppleTVSimulator {
 #endif
 #endif
         },
-        GetXcodeSDKDir("AppleTVSimulator.Internal.sdk", "AppleTVSimulator.sdk"),
+        "AppleTVSimulator.Internal.sdk", "AppleTVSimulator.sdk",
         XcodeSDK::Type::AppleTVSimulator,
         CoreSimulatorSupport::DeviceType::ProductFamilyID::appleTV, force,
         arch);
@@ -646,7 +645,7 @@ struct PlatformAppleWatchSimulator {
 #endif
 #endif
         },
-        GetXcodeSDKDir("WatchSimulator.Internal.sdk", "WatchSimulator.sdk"),
+        "WatchSimulator.Internal.sdk", "WatchSimulator.sdk",
         XcodeSDK::Type::WatchSimulator,
         CoreSimulatorSupport::DeviceType::ProductFamilyID::appleWatch, force,
         arch);

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

@@ -59,7 +59,8 @@ class PlatformAppleSimulator : public PlatformDarwin {
                  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);