[Multilib] Custom flags YAML parsing

This patch adds support for custom flags in the multilib YAML file.

Details about this change can be found in this thread:
https://discourse.llvm.org/t/rfc-multilib-custom-flags/81058

Author: vhscampos

clang/include/clang/Driver/Multilib.h

@@ -118,17 +118,26 @@ class MultilibSet {
     std::vector<std::string> Flags;
   };
 
+  struct CustomFlagDeclaration {
+    std::string Name;
+    SmallVector<std::string> Values;
+    std::string DefaultValue;
+  };
+
 private:
   multilib_list Multilibs;
-  std::vector<FlagMatcher> FlagMatchers;
+  SmallVector<FlagMatcher> FlagMatchers;
+  SmallVector<CustomFlagDeclaration> CustomFlagDecls;
   IncludeDirsFunc IncludeCallback;
   IncludeDirsFunc FilePathsCallback;
 
 public:
   MultilibSet() = default;
   MultilibSet(multilib_list &&Multilibs,
-              std::vector<FlagMatcher> &&FlagMatchers = {})
-      : Multilibs(Multilibs), FlagMatchers(FlagMatchers) {}
+              SmallVector<FlagMatcher> &&FlagMatchers = {},
+              SmallVector<CustomFlagDeclaration> &&CustomFlagDecls = {})
+      : Multilibs(std::move(Multilibs)), FlagMatchers(std::move(FlagMatchers)),
+        CustomFlagDecls(std::move(CustomFlagDecls)) {}
 
   const multilib_list &getMultilibs() { return Multilibs; }
 

clang/lib/Driver/Multilib.cpp

@@ -207,9 +207,10 @@ struct MultilibGroupSerialization {
 
 struct MultilibSetSerialization {
   llvm::VersionTuple MultilibVersion;
-  std::vector<MultilibGroupSerialization> Groups;
-  std::vector<MultilibSerialization> Multilibs;
-  std::vector<MultilibSet::FlagMatcher> FlagMatchers;
+  SmallVector<MultilibGroupSerialization> Groups;
+  SmallVector<MultilibSerialization> Multilibs;
+  SmallVector<MultilibSet::FlagMatcher> FlagMatchers;
+  SmallVector<MultilibSet::CustomFlagDeclaration> CustomFlagDeclarations;
 };
 
 } // end anonymous namespace
@@ -261,11 +262,31 @@ template <> struct llvm::yaml::MappingTraits<MultilibSet::FlagMatcher> {
   }
 };
 
+template <>
+struct llvm::yaml::MappingTraits<MultilibSet::CustomFlagDeclaration> {
+  static void mapping(llvm::yaml::IO &io,
+                      MultilibSet::CustomFlagDeclaration &V) {
+    io.mapRequired("Name", V.Name);
+    io.mapRequired("Values", V.Values);
+    io.mapRequired("Default", V.DefaultValue);
+  }
+  static std::string validate(IO &io, MultilibSet::CustomFlagDeclaration &V) {
+    if (V.Name.empty())
+      return "name required for custom flag";
+    if (V.Values.empty())
+      return "at least one value is expected";
+    if (!llvm::is_contained(V.Values, V.DefaultValue))
+      return "default value is not one of the possible listed values";
+    return {};
+  }
+};
+
 template <> struct llvm::yaml::MappingTraits<MultilibSetSerialization> {
   static void mapping(llvm::yaml::IO &io, MultilibSetSerialization &M) {
     io.mapRequired("MultilibVersion", M.MultilibVersion);
     io.mapRequired("Variants", M.Multilibs);
     io.mapOptional("Groups", M.Groups);
+    io.mapOptional("Flags", M.CustomFlagDeclarations);
     io.mapOptional("Mappings", M.FlagMatchers);
   }
   static std::string validate(IO &io, MultilibSetSerialization &M) {
@@ -297,6 +318,7 @@ template <> struct llvm::yaml::MappingTraits<MultilibSetSerialization> {
 LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibSerialization)
 LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibGroupSerialization)
 LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibSet::FlagMatcher)
+LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibSet::CustomFlagDeclaration)
 
 llvm::ErrorOr<MultilibSet>
 MultilibSet::parseYaml(llvm::MemoryBufferRef Input,
@@ -325,7 +347,8 @@ MultilibSet::parseYaml(llvm::MemoryBufferRef Input,
     }
   }
 
-  return MultilibSet(std::move(Multilibs), std::move(MS.FlagMatchers));
+  return MultilibSet(std::move(Multilibs), std::move(MS.FlagMatchers),
+                     std::move(MS.CustomFlagDeclarations));
 }
 
 LLVM_DUMP_METHOD void MultilibSet::dump() const {