[clang] [llvm] [AArch64TargetParser]Fix reconstructFromParsedFeatures ignoring negative features (PR #142236)

[Alexandros Lamprineas via llvm-commits]

================
@@ -1831,6 +1831,22 @@ TEST_P(AArch64ExtensionDependenciesBaseCPUTestFixture,
   }
 }
 
+TEST(TargetParserTest, testAArch64ReconstructFromParsedFeatures) {
+  AArch64::ExtensionSet Extensions;
+  std::vector<std::string> FeatureOptions = {
+      "-sve2", "-Baz", "+sve", "+FooBar", "+sve2", "+neon", "-sve",
+  };
+  std::vector<std::string> NonExtensions;
+  Extensions.reconstructFromParsedFeatures(FeatureOptions, NonExtensions);
+
+  std::vector<std::string> NonExtensionsExpected = {"-Baz", "+FooBar"};
+  ASSERT_THAT(NonExtensions, testing::ContainerEq(NonExtensionsExpected));
+  std::vector<StringRef> Features;
+  Extensions.toLLVMFeatureList(Features);
+  std::vector<StringRef> FeaturesExpected = {"+neon", "-sve", "+sve2"};
----------------
labrinea wrote:

>  If you look at the code it does Enabled.reset which should remove a feature and its dependencies.

Actually I was mistaken, `Enabled.reset` should not transitively remove dependencies. Calling`disable()` would do that, but as I said this is probably redundant since the command line arguments have been processed at this stage.

This code inside `reconstructFromParsedFeatures` seems dead
```
if (IsNegated)
  Enabled.reset(AE->ID);
```

https://github.com/llvm/llvm-project/pull/142236