[Multilib] Custom flags YAML parsing (#122903)

This patch is the first step to extend the current multilib system to
support the selection of library variants which do not correspond to
existing command-line options.

Proposal can be found in
https://discourse.llvm.org/t/rfc-multilib-custom-flags/81058

The multilib mechanism supports libraries that target code generation or
language options such as `--target`, `-mcpu`, `-mfpu`,
`-mbranch-protection`. However, some library variants are particular to
features that do not correspond to any command-line options. Examples
include variants for multithreading and semihosting.

This work introduces a way to instruct the multilib system to consider
these features in library selection. This particular patch comprises a
new section in `multilib.yaml` to declare flags for which no option
exists. Henceforth this sort of flag will be called `custom flag` for
clarity.

The `multilib.yaml` file will have a new section called Flags which
contains the declarations of the target’s custom flags:

```yaml
Flags:
- Name: multithreaded
  Values:
  - Name: no-multithreaded
    MacroDefines: [__SINGLE_THREAD__]
  - Name: multithreaded
  Default: no-multithreaded

- Name: io
  Values:
    - Name: io-none
    - Name: io-semihosting
      MacroDefines: [SEMIHOSTING]
    - Name: io-linux-syscalls
      MacroDefines: [LINUX_SYSCALLS, HOSTED=1]
   Default: io-none
```
- Name: the name to categorize a flag.
- Values: a list of possible values.
- Default: it specifies which value this flag should take if not
specified in the command-line invocation. It must be one value from the
Values field.

Each flag Value follows this description:
- Name (required): the name of the custom flag value (string). This is
the string to be used in `-fmultilib-flag=<string>`.
- MacroDefines (optional): a list of strings to be used as macro
definitions. Each string
  is fed into the driver as ``-D<string>``.

A Default value is useful to save users from specifying custom flags
that have a most commonly used value.

The namespace of flag values is common across all flags. This means that
flag values must be unique.

Author: vhscampos

clang/include/clang/Driver/Multilib.h

@@ -101,6 +101,30 @@ class Multilib {
 
 raw_ostream &operator<<(raw_ostream &OS, const Multilib &M);
 
+namespace custom_flag {
+struct Declaration;
+
+struct ValueDetail {
+  std::string Name;
+  std::optional<SmallVector<std::string>> MacroDefines;
+  Declaration *Decl;
+};
+
+struct Declaration {
+  std::string Name;
+  SmallVector<ValueDetail> ValueList;
+  std::optional<size_t> DefaultValueIdx;
+
+  Declaration() = default;
+  Declaration(const Declaration &);
+  Declaration(Declaration &&);
+  Declaration &operator=(const Declaration &);
+  Declaration &operator=(Declaration &&);
+};
+
+static constexpr StringRef Prefix = "-fmultilib-flag=";
+} // namespace custom_flag
+
 /// See also MultilibSetBuilder for combining multilibs into a set.
 class MultilibSet {
 public:
@@ -120,15 +144,18 @@ class MultilibSet {
 
 private:
   multilib_list Multilibs;
-  std::vector<FlagMatcher> FlagMatchers;
+  SmallVector<FlagMatcher> FlagMatchers;
+  SmallVector<custom_flag::Declaration> CustomFlagDecls;
   IncludeDirsFunc IncludeCallback;
   IncludeDirsFunc FilePathsCallback;
 
 public:
   MultilibSet() = default;
   MultilibSet(multilib_list &&Multilibs,
-              std::vector<FlagMatcher> &&FlagMatchers = {})
-      : Multilibs(Multilibs), FlagMatchers(FlagMatchers) {}
+              SmallVector<FlagMatcher> &&FlagMatchers = {},
+              SmallVector<custom_flag::Declaration> &&CustomFlagDecls = {})
+      : Multilibs(std::move(Multilibs)), FlagMatchers(std::move(FlagMatchers)),
+        CustomFlagDecls(std::move(CustomFlagDecls)) {}
 
   const multilib_list &getMultilibs() { return Multilibs; }
 

clang/lib/Driver/Multilib.cpp

@@ -10,6 +10,7 @@
 #include "clang/Basic/LLVM.h"
 #include "clang/Driver/Driver.h"
 #include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -201,13 +202,20 @@ 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<custom_flag::Declaration> CustomFlagDeclarations;
 };
 
 } // end anonymous namespace
 
+LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibSerialization)
+LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibGroupSerialization)
+LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibSet::FlagMatcher)
+LLVM_YAML_IS_SEQUENCE_VECTOR(custom_flag::ValueDetail)
+LLVM_YAML_IS_SEQUENCE_VECTOR(custom_flag::Declaration)
+
 template <> struct llvm::yaml::MappingTraits<MultilibSerialization> {
   static void mapping(llvm::yaml::IO &io, MultilibSerialization &V) {
     io.mapOptional("Dir", V.Dir);
@@ -255,11 +263,61 @@ template <> struct llvm::yaml::MappingTraits<MultilibSet::FlagMatcher> {
   }
 };
 
+template <>
+struct llvm::yaml::MappingContextTraits<custom_flag::ValueDetail,
+                                        llvm::SmallSet<std::string, 32>> {
+  static void mapping(llvm::yaml::IO &io, custom_flag::ValueDetail &V,
+                      llvm::SmallSet<std::string, 32> &) {
+    io.mapRequired("Name", V.Name);
+    io.mapOptional("MacroDefines", V.MacroDefines);
+  }
+  static std::string validate(IO &io, custom_flag::ValueDetail &V,
+                              llvm::SmallSet<std::string, 32> &NameSet) {
+    if (V.Name.empty())
+      return "custom flag value requires a name";
+    if (!NameSet.insert(V.Name).second)
+      return "duplicate custom flag value name: \"" + V.Name + "\"";
+    return {};
+  }
+};
+
+template <>
+struct llvm::yaml::MappingContextTraits<custom_flag::Declaration,
+                                        llvm::SmallSet<std::string, 32>> {
+  static void mapping(llvm::yaml::IO &io, custom_flag::Declaration &V,
+                      llvm::SmallSet<std::string, 32> &NameSet) {
+    io.mapRequired("Name", V.Name);
+    io.mapRequired("Values", V.ValueList, NameSet);
+    std::string DefaultValueName;
+    io.mapRequired("Default", DefaultValueName);
+
+    for (auto [Idx, Value] : llvm::enumerate(V.ValueList)) {
+      Value.Decl = &V;
+      if (Value.Name == DefaultValueName) {
+        assert(!V.DefaultValueIdx);
+        V.DefaultValueIdx = Idx;
+      }
+    }
+  }
+  static std::string validate(IO &io, custom_flag::Declaration &V,
+                              llvm::SmallSet<std::string, 32> &) {
+    if (V.Name.empty())
+      return "custom flag requires a name";
+    if (V.ValueList.empty())
+      return "custom flag must have at least one value";
+    if (!V.DefaultValueIdx)
+      return "custom flag must have a default value";
+    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);
+    llvm::SmallSet<std::string, 32> NameSet;
+    io.mapOptionalWithContext("Flags", M.CustomFlagDeclarations, NameSet);
     io.mapOptional("Mappings", M.FlagMatchers);
   }
   static std::string validate(IO &io, MultilibSetSerialization &M) {
@@ -288,10 +346,6 @@ 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::ErrorOr<MultilibSet>
 MultilibSet::parseYaml(llvm::MemoryBufferRef Input,
                        llvm::SourceMgr::DiagHandlerTy DiagHandler,
@@ -319,7 +373,8 @@ 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 {
@@ -335,3 +390,41 @@ raw_ostream &clang::driver::operator<<(raw_ostream &OS, const MultilibSet &MS) {
   MS.print(OS);
   return OS;
 }
+
+namespace clang::driver::custom_flag {
+Declaration::Declaration(const Declaration &Other)
+    : Name(Other.Name), ValueList(Other.ValueList),
+      DefaultValueIdx(Other.DefaultValueIdx) {
+  for (ValueDetail &Detail : ValueList)
+    Detail.Decl = this;
+}
+
+Declaration::Declaration(Declaration &&Other)
+    : Name(std::move(Other.Name)), ValueList(std::move(Other.ValueList)),
+      DefaultValueIdx(std::move(Other.DefaultValueIdx)) {
+  for (ValueDetail &Detail : ValueList)
+    Detail.Decl = this;
+}
+
+Declaration &Declaration::operator=(const Declaration &Other) {
+  if (this == &Other)
+    return *this;
+  Name = Other.Name;
+  ValueList = Other.ValueList;
+  DefaultValueIdx = Other.DefaultValueIdx;
+  for (ValueDetail &Detail : ValueList)
+    Detail.Decl = this;
+  return *this;
+}
+
+Declaration &Declaration::operator=(Declaration &&Other) {
+  if (this == &Other)
+    return *this;
+  Name = std::move(Other.Name);
+  ValueList = std::move(Other.ValueList);
+  DefaultValueIdx = std::move(Other.DefaultValueIdx);
+  for (ValueDetail &Detail : ValueList)
+    Detail.Decl = this;
+  return *this;
+}
+} // namespace clang::driver::custom_flag

clang/test/Driver/baremetal-multilib-custom-flags-parsing.yaml

@@ -0,0 +1,133 @@
+# RUN: split-file %s %t
+
+# RUN: %clang --target=arm-none-eabi --multi-lib-config=%t/multilib-without-macro-defines.yaml %s -### -o /dev/null 2>&1 \
+# RUN: | FileCheck %s
+# RUN: %clang --target=arm-none-eabi --multi-lib-config=%t/multilib-with-macro-defines.yaml %s -### -o /dev/null 2>&1 \
+# RUN: | FileCheck %s
+# CHECK-NOT: error:
+
+# RUN: %clang --target=arm-none-eabi --multi-lib-config=%t/missing-flag-name.yaml %s -### -o /dev/null 2>&1 \
+# RUN: | FileCheck %s --check-prefix=CHECK-MISSING-FLAG-NAME
+# CHECK-MISSING-FLAG-NAME: error: custom flag requires a name
+
+# RUN: %clang --target=arm-none-eabi --multi-lib-config=%t/missing-flag-values.yaml %s -### -o /dev/null 2>&1 \
+# RUN: | FileCheck %s --check-prefix=CHECK-MISSING-FLAG-VALUES
+# CHECK-MISSING-FLAG-VALUES: error: custom flag must have at least one value
+
+# RUN: %clang --target=arm-none-eabi --multi-lib-config=%t/missing-flag-value-default.yaml %s -### -o /dev/null 2>&1 \
+# RUN: | FileCheck %s --check-prefix=CHECK-MISSING-FLAG-VALUE-DEFAULT
+# CHECK-MISSING-FLAG-VALUE-DEFAULT: error: custom flag must have a default value
+
+# RUN: %clang --target=arm-none-eabi --multi-lib-config=%t/missing-flag-value-name.yaml %s -### -o /dev/null 2>&1 \
+# RUN: | FileCheck %s --check-prefix=CHECK-MISSING-FLAG-VALUE-NAME
+# CHECK-MISSING-FLAG-VALUE-NAME: error: custom flag value requires a name
+
+# RUN: %clang --target=arm-none-eabi --multi-lib-config=%t/duplicate-flag-value-name.yaml %s -### -o /dev/null 2>&1 \
+# RUN: | FileCheck %s --check-prefix=CHECK-DUPLICATE-FLAG-VALUE-NAME
+# CHECK-DUPLICATE-FLAG-VALUE-NAME:      error: duplicate custom flag value name: "value-name"
+# CHECK-DUPLICATE-FLAG-VALUE-NAME-NEXT: - Name: value-name
+
+#--- multilib-without-macro-defines.yaml
+---
+MultilibVersion: 1.0
+
+Variants:
+- Dir: libc
+  Flags: [-fmultilib-flag=a]
+
+Flags:
+  - Name: flag
+    Values:
+    - Name: a
+    - Name: b
+    Default: a
+
+#--- multilib-with-macro-defines.yaml
+---
+MultilibVersion: 1.0
+
+Variants:
+- Dir: libc
+  Flags: [-fmultilib-flag=a]
+
+Flags:
+  - Name: flag
+    Values:
+    - Name: a
+      MacroDefines: [FEATURE_A]
+    - Name: b
+      MacroDefines: [FEATURE_B]
+    Default: a
+
+#--- missing-flag-name.yaml
+---
+MultilibVersion: 1.0
+
+Variants:
+- Dir: libc
+  Flags: [-fmultilib-flag=a]
+
+Flags:
+  - Values:
+    - Name: a
+    Default: a
+
+#--- missing-flag-values.yaml
+---
+MultilibVersion: 1.0
+
+Variants:
+- Dir: libc
+  Flags: [-fmultilib-flag=a]
+
+Flags:
+  - Name: flag
+    Values:
+    Default: a
+
+#--- missing-flag-value-default.yaml
+---
+MultilibVersion: 1.0
+
+Variants:
+- Dir: libc
+  Flags: [-fmultilib-flag=a]
+
+Flags:
+  - Name: flag
+    Values:
+    - Name: a
+    Default:
+
+#--- missing-flag-value-name.yaml
+---
+MultilibVersion: 1.0
+
+Variants:
+- Dir: libc
+  Flags: [-fmultilib-flag=a]
+
+Flags:
+  - Name: flag
+    Values:
+    - Name:
+    Default: a
+
+#--- duplicate-flag-value-name.yaml
+---
+MultilibVersion: 1.0
+
+Variants:
+- Dir: libc
+  Flags: [-fmultilib-flag=value-name]
+
+Flags:
+  - Name: a
+    Values:
+    - Name: value-name
+    - Name: value-a
+    Default: value-name
+  - Name: b
+    Values:
+    - Name: value-name
+    Default: value-name