Clean up and improve install-directory locating

Another unclear edge case where UIforETW can't find the WPT install
location was reported. An extraneous "else" probably made this problem
worse, but in addition to removing that this change also cleans up the
code and adds the reading of another registry key.

This should resolve issue #159.

UIforETW/UIforETWDlg.cpp

@@ -337,46 +337,71 @@ void CUIforETWDlg::CheckSymbolDLLs()
 
 void CUIforETWDlg::GetInstallFolder()
 {
-	// The WPT installer is always a 32-bit installer, so we look for it in
+	// The WPT installer is (was?) always a 32-bit installer, so we look for it in
 	// ProgramFilesX86 / WOW6432Node, on 32-bit and 64-bit operating systems.
 	wpt10Dir_ = ReadRegistryString(HKEY_LOCAL_MACHINE, L"SOFTWARE\\Microsoft\\Microsoft SDKs\\Windows\\v10.0", L"InstallationFolder", true);
 	if (!wpt10Dir_.empty())
 	{
 		EnsureEndsWithDirSeparator(wpt10Dir_);
 		wpt10Dir_ += L"Windows Performance Toolkit\\";
+		if (!PathFileExists((wpt10Dir_ + L"xperf.exe").c_str()))
+			wpt10Dir_.clear();
 	}
 
-	// Look for alternate install paths if needed.
+	// Some users (issue #159) reported that the registry key above doesn't work,
+	// and that this registry key should be used instead.
+	if (wpt10Dir_.empty())
+	{
+		// Other sources suggest looking here:
+		// HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Windows Kits\Installed Roots
+		// https://stackoverflow.com/questions/35119223/how-to-programmatically-detect-and-locate-the-windows-10-sdk/35121768#35121768
+		wpt10Dir_ = ReadRegistryString(HKEY_LOCAL_MACHINE, L"SOFTWARE\\WOW6432Node\\Microsoft\\Windows Kits\\Installed Roots", L"KitsRoot10", true);
+		EnsureEndsWithDirSeparator(wpt10Dir_);
+		wpt10Dir_ += L"Windows Performance Toolkit\\";
+		if (!PathFileExists((wpt10Dir_ + L"xperf.exe").c_str()))
+			wpt10Dir_.clear();
+	}
+
+	// Look for alternate install paths if needed. This was needed in 2023 for
+	// when UIforETW installed WPT without first installing the SDK, causing WPT to
+	// be installed into the 64-bit program files directory, but with no
+	// InstallationFolder reg key. It's not clear whether KitsRoot10 resolves this.
+	const wchar_t* const suffix = L"\\Windows Kits\\10\\Windows Performance Toolkit\\";
+	std::wstring windowsKits86Dir;
 	{
-		const wchar_t* const suffix = L"\\Windows Kits\\10\\Windows Performance Toolkit\\";
 		wchar_t* progFilesx86Dir = nullptr;
 		if (!SUCCEEDED(SHGetKnownFolderPath(FOLDERID_ProgramFilesX86, 0, nullptr, &progFilesx86Dir)))
 			std::terminate();
-		std::wstring windowsKits86Dir = progFilesx86Dir;
+		windowsKits86Dir = progFilesx86Dir;
 		CoTaskMemFree(progFilesx86Dir);
 		windowsKits86Dir += suffix;
+	}
 
+	std::wstring windowsKitsDir;
+	{
 		wchar_t* progFilesDir = nullptr;
 		if (!SUCCEEDED(SHGetKnownFolderPath(FOLDERID_ProgramFiles, 0, nullptr, &progFilesDir)))
 			std::terminate();
-		std::wstring windowsKitsDir = progFilesDir;
+		windowsKitsDir = progFilesDir;
 		CoTaskMemFree(progFilesDir);
 		windowsKitsDir += suffix;
+	}
 
-		// If the registry entries were unavailable, fall back to assuming their installation directory.
-		// Starting with the 22H2 SDK this is the ProgramFiles directory rather than ProgramFilesX86
-		if (wpt10Dir_.empty())
-		{
+	// If the registry entries were unavailable, fall back to assuming their installation directory.
+	// Starting with the 22H2 SDK this is the ProgramFiles directory rather than ProgramFilesX86
+	if (wpt10Dir_.empty())
+	{
+		wpt10Dir_ = windowsKitsDir;
+	}
+
+	// If xperf.exe doesn't exist in wpt10Dir_ and it does exist in one of the two
+	// default paths then switch to that.
+	if (!PathFileExists((wpt10Dir_ + L"xperf.exe").c_str()))
+	{
+		if (PathFileExists((windowsKits86Dir + L"xperf.exe").c_str()))
+			wpt10Dir_ = windowsKits86Dir;
+		else if (PathFileExists((windowsKitsDir + L"xperf.exe").c_str()))
 			wpt10Dir_ = windowsKitsDir;
-		}
-		// If xperf.exe doesn't exist in wpt10Dir_ and it does exist elsewhere, switch to that.
-		else if (!PathFileExists((wpt10Dir_ + L"xperf.exe").c_str()))
-		{
-			if (PathFileExists((windowsKits86Dir + L"xperf.exe").c_str()))
-				wpt10Dir_ = windowsKits86Dir;
-			else if (PathFileExists((windowsKitsDir + L"xperf.exe").c_str()))
-				wpt10Dir_ = windowsKitsDir;
-		}
 	}
 }