diff --git a/clang/unittests/Frontend/CompilerInvocationTest.cpp b/clang/unittests/Frontend/CompilerInvocationTest.cpp
--- a/clang/unittests/Frontend/CompilerInvocationTest.cpp
+++ b/clang/unittests/Frontend/CompilerInvocationTest.cpp
@@ -77,6 +77,155 @@
   ASSERT_TRUE(Invocation.getFrontendOpts().UseTemporary);
 }
 
+// Boolean option with a keypath that defaults to true.
+// The flag with negative spelling can set the keypath to false.
+// The flag with positive spelling can reset the keypath to true.
+
+TEST_F(CommandLineTest, BoolOptionDefaultTruePresentNone) {
+  const char *Args[] = {""};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_FALSE(Diags->hasErrorOccurred());
+  ASSERT_TRUE(Invocation.getCodeGenOpts().Autolink);
+
+  // TODO: Test argument generation.
+}
+
+TEST_F(CommandLineTest, BoolOptionDefaultTruePresentNegChange) {
+  const char *Args[] = {"-fno-autolink"};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_FALSE(Diags->hasErrorOccurred());
+  ASSERT_FALSE(Invocation.getCodeGenOpts().Autolink);
+
+  // TODO: Test argument generation.
+}
+
+TEST_F(CommandLineTest, BoolOptionDefaultTruePresentPosReset) {
+  const char *Args[] = {"-fautolink"};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_TRUE(Diags->hasErrorOccurred()); // Driver-only flag.
+  ASSERT_TRUE(Invocation.getCodeGenOpts().Autolink);
+}
+
+// Boolean option with a keypath that defaults to false.
+// The flag with negative spelling can set the keypath to true.
+// The flag with positive spelling can reset the keypath to false.
+
+TEST_F(CommandLineTest, BoolOptionDefaultFalsePresentNone) {
+  const char *Args[] = {""};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_FALSE(Diags->hasErrorOccurred());
+  ASSERT_FALSE(Invocation.getCodeGenOpts().NoInlineLineTables);
+
+  // TODO: Test argument generation.
+}
+
+TEST_F(CommandLineTest, BoolOptionDefaultFalsePresentNegChange) {
+  const char *Args[] = {"-gno-inline-line-tables"};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_FALSE(Diags->hasErrorOccurred());
+  ASSERT_TRUE(Invocation.getCodeGenOpts().NoInlineLineTables);
+
+  // TODO: Test argument generation.
+}
+
+TEST_F(CommandLineTest, BoolOptionDefaultFalsePresentPosReset) {
+  const char *Args[] = {"-ginline-line-tables"};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_TRUE(Diags->hasErrorOccurred()); // Driver-only flag.
+  ASSERT_FALSE(Invocation.getCodeGenOpts().NoInlineLineTables);
+}
+
+// Boolean option with a keypath that defaults to false.
+// The flag with positive spelling can set the keypath to true.
+// The flag with negative spelling can reset the keypath to false.
+
+TEST_F(CommandLineTest, BoolOptionDefaultFalsePresentNoneX) {
+  const char *Args[] = {""};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_FALSE(Diags->hasErrorOccurred());
+  ASSERT_FALSE(Invocation.getCodeGenOpts().CodeViewGHash);
+
+  // TODO: Test argument generation.
+}
+
+TEST_F(CommandLineTest, BoolOptionDefaultFalsePresentPosChange) {
+  const char *Args[] = {"-gcodeview-ghash"};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_FALSE(Diags->hasErrorOccurred());
+  ASSERT_TRUE(Invocation.getCodeGenOpts().CodeViewGHash);
+
+  // TODO: Test argument generation.
+}
+
+TEST_F(CommandLineTest, BoolOptionDefaultFalsePresentNegReset) {
+  const char *Args[] = {"-gno-codeview-ghash"};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_TRUE(Diags->hasErrorOccurred()); // Driver-only flag.
+  ASSERT_FALSE(Invocation.getCodeGenOpts().CodeViewGHash);
+}
+
+// Boolean option with a keypath that defaults to an arbitrary expression.
+// The flag with positive spelling can set the keypath to true.
+// The flag with negative spelling can set the keypath to false.
+
+static constexpr unsigned PassManagerDefault =
+    !static_cast<unsigned>(LLVM_ENABLE_NEW_PASS_MANAGER);
+
+static constexpr const char *PassManagerResetByFlag =
+    LLVM_ENABLE_NEW_PASS_MANAGER ? "-fno-legacy-pass-manager"
+                                 : "-flegacy-pass-manager";
+
+static constexpr const char *PassManagerChangedByFlag =
+    LLVM_ENABLE_NEW_PASS_MANAGER ? "-flegacy-pass-manager"
+                                 : "-fno-legacy-pass-manager";
+
+TEST_F(CommandLineTest, BoolOptionDefaultArbitraryTwoFlagsPresentNone) {
+  const char *Args = {""};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+
+  ASSERT_FALSE(Diags->hasErrorOccurred());
+  ASSERT_EQ(Invocation.getCodeGenOpts().LegacyPassManager, PassManagerDefault);
+
+  Invocation.generateCC1CommandLine(GeneratedArgs, *this);
+
+  ASSERT_THAT(GeneratedArgs, Contains(StrEq(PassManagerResetByFlag)));
+  ASSERT_THAT(GeneratedArgs, Not(Contains(StrEq(PassManagerChangedByFlag))));
+}
+
+TEST_F(CommandLineTest, BoolOptionDefaultArbitraryTwoFlagsPresentChange) {
+  const char *Args[] = {PassManagerChangedByFlag};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_FALSE(Diags->hasErrorOccurred());
+  ASSERT_EQ(Invocation.getCodeGenOpts().LegacyPassManager, !PassManagerDefault);
+
+  Invocation.generateCC1CommandLine(GeneratedArgs, *this);
+  ASSERT_THAT(GeneratedArgs, Contains(StrEq(PassManagerChangedByFlag)));
+  ASSERT_THAT(GeneratedArgs, Not(Contains(StrEq(PassManagerResetByFlag))));
+}
+
+TEST_F(CommandLineTest, BoolOptionDefaultArbitraryTwoFlagsPresentReset) {
+  const char *Args[] = {PassManagerResetByFlag};
+
+  CompilerInvocation::CreateFromArgs(Invocation, Args, *Diags);
+  ASSERT_FALSE(Diags->hasErrorOccurred());
+  ASSERT_EQ(Invocation.getCodeGenOpts().LegacyPassManager, PassManagerDefault);
+
+  Invocation.generateCC1CommandLine(GeneratedArgs, *this);
+  ASSERT_THAT(GeneratedArgs, Contains(StrEq(PassManagerResetByFlag)));
+  ASSERT_THAT(GeneratedArgs, Not(Contains(StrEq(PassManagerChangedByFlag))));
+}
+
 TEST_F(CommandLineTest, CanGenerateCC1CommandLineFlag) {
   const char *Args[] = {"-fmodules-strict-context-hash"};