[Driver] Add ExclusiveGroup feature to multilib.yaml.

clang/include/clang/Driver/Multilib.h

@@ -39,13 +39,22 @@ class Multilib {
   std::string IncludeSuffix;
   flags_list Flags;
 
+  // Optionally, a multilib can be assigned a string tag indicating that it's
+  // part of a group of mutually exclusive possibilities. If two or more
+  // multilibs have the same non-empty value of ExclusiveGroup, then only the
+  // last matching one of them will be selected.
+  //
+  // Setting this to the empty string is a special case, indicating that the
+  // directory is not mutually exclusive with anything else.
+  std::string ExclusiveGroup;
+
 public:
   /// GCCSuffix, OSSuffix & IncludeSuffix will be appended directly to the
   /// sysroot string so they must either be empty or begin with a '/' character.
   /// This is enforced with an assert in the constructor.
   Multilib(StringRef GCCSuffix = {}, StringRef OSSuffix = {},
-           StringRef IncludeSuffix = {},
-           const flags_list &Flags = flags_list());
+           StringRef IncludeSuffix = {}, const flags_list &Flags = flags_list(),
+           StringRef ExclusiveGroup = {});
 
   /// Get the detected GCC installation path suffix for the multi-arch
   /// target variant. Always starts with a '/', unless empty
@@ -63,6 +72,9 @@ class Multilib {
   /// All elements begin with either '-' or '!'
   const flags_list &flags() const { return Flags; }
 
+  /// Get the exclusive group label.
+  const std::string &exclusiveGroup() const { return ExclusiveGroup; }
+
   LLVM_DUMP_METHOD void dump() const;
   /// print summary of the Multilib
   void print(raw_ostream &OS) const;

clang/lib/Driver/Multilib.cpp

@@ -9,6 +9,7 @@
 #include "clang/Driver/Multilib.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/Version.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Compiler.h"
@@ -29,9 +30,10 @@ using namespace driver;
 using namespace llvm::sys;
 
 Multilib::Multilib(StringRef GCCSuffix, StringRef OSSuffix,
-                   StringRef IncludeSuffix, const flags_list &Flags)
+                   StringRef IncludeSuffix, const flags_list &Flags,
+                   StringRef ExclusiveGroup)
     : GCCSuffix(GCCSuffix), OSSuffix(OSSuffix), IncludeSuffix(IncludeSuffix),
-      Flags(Flags) {
+      Flags(Flags), ExclusiveGroup(ExclusiveGroup) {
   assert(GCCSuffix.empty() ||
          (StringRef(GCCSuffix).front() == '/' && GCCSuffix.size() > 1));
   assert(OSSuffix.empty() ||
@@ -96,13 +98,37 @@ bool MultilibSet::select(const Multilib::flags_list &Flags,
                          llvm::SmallVector<Multilib> &Selected) const {
   llvm::StringSet<> FlagSet(expandFlags(Flags));
   Selected.clear();
-  llvm::copy_if(Multilibs, std::back_inserter(Selected),
-                [&FlagSet](const Multilib &M) {
-                  for (const std::string &F : M.flags())
-                    if (!FlagSet.contains(F))
-                      return false;
-                  return true;
-                });
+
+  // Decide which multilibs we're going to select at all.
+  llvm::DenseSet<StringRef> ExclusiveGroupsSelected;
+  for (const Multilib &M : llvm::reverse(Multilibs)) {
+    // If this multilib doesn't match all our flags, don't select it.
+    if (!llvm::all_of(M.flags(), [&FlagSet](const std::string &F) {
+          return FlagSet.contains(F);
+        }))
+      continue;
+
+    const std::string &group = M.exclusiveGroup();
+    if (!group.empty()) {
+      // If this multilib has the same ExclusiveGroup as one we've already
+      // selected, skip it. We're iterating in reverse order, so the group
+      // member we've selected already is preferred.
+      //
+      // Otherwise, add the group name to the set of groups we've already
+      // selected a member of.
+      auto [It, Inserted] = ExclusiveGroupsSelected.insert(group);
+      if (!Inserted)
+        continue;
+    }
+
+    // Select this multilib.
+    Selected.push_back(M);
+  }
+
+  // We iterated in reverse order, so now put Selected back the right way
+  // round.
+  std::reverse(Selected.begin(), Selected.end());
+
   return !Selected.empty();
 }
 
@@ -138,10 +164,39 @@ static const VersionTuple MultilibVersionCurrent(1, 0);
 struct MultilibSerialization {
   std::string Dir;
   std::vector<std::string> Flags;
+  std::string Group;
+};
+
+enum class MultilibGroupType {
+  /*
+   * The only group type currently supported is 'Exclusive', which indicates a
+   * group of multilibs of which at most one may be selected.
+   */
+  Exclusive,
+
+  /*
+   * Future possibility: a second group type indicating a set of library
+   * directories that are mutually _dependent_ rather than mutually exclusive:
+   * if you include one you must include them all.
+   *
+   * It might also be useful to allow groups to be members of other groups, so
+   * that a mutually exclusive group could contain a mutually dependent set of
+   * library directories, or vice versa.
+   *
+   * These additional features would need changes in the implementation, but
+   * the YAML schema is set up so they can be added without requiring changes
+   * in existing users' multilib.yaml files.
+   */
+};
+
+struct MultilibGroupSerialization {
+  std::string Name;
+  MultilibGroupType Type;
 };
 
 struct MultilibSetSerialization {
   llvm::VersionTuple MultilibVersion;
+  std::vector<MultilibGroupSerialization> Groups;
   std::vector<MultilibSerialization> Multilibs;
   std::vector<MultilibSet::FlagMatcher> FlagMatchers;
 };
@@ -152,6 +207,7 @@ template <> struct llvm::yaml::MappingTraits<MultilibSerialization> {
   static void mapping(llvm::yaml::IO &io, MultilibSerialization &V) {
     io.mapRequired("Dir", V.Dir);
     io.mapRequired("Flags", V.Flags);
+    io.mapOptional("Group", V.Group);
   }
   static std::string validate(IO &io, MultilibSerialization &V) {
     if (StringRef(V.Dir).starts_with("/"))
@@ -160,6 +216,19 @@ template <> struct llvm::yaml::MappingTraits<MultilibSerialization> {
   }
 };
 
+template <> struct llvm::yaml::ScalarEnumerationTraits<MultilibGroupType> {
+  static void enumeration(IO &io, MultilibGroupType &Val) {
+    io.enumCase(Val, "Exclusive", MultilibGroupType::Exclusive);
+  }
+};
+
+template <> struct llvm::yaml::MappingTraits<MultilibGroupSerialization> {
+  static void mapping(llvm::yaml::IO &io, MultilibGroupSerialization &V) {
+    io.mapRequired("Name", V.Name);
+    io.mapRequired("Type", V.Type);
+  }
+};
+
 template <> struct llvm::yaml::MappingTraits<MultilibSet::FlagMatcher> {
   static void mapping(llvm::yaml::IO &io, MultilibSet::FlagMatcher &M) {
     io.mapRequired("Match", M.Match);
@@ -180,6 +249,7 @@ 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("Mappings", M.FlagMatchers);
   }
   static std::string validate(IO &io, MultilibSetSerialization &M) {
@@ -191,11 +261,25 @@ template <> struct llvm::yaml::MappingTraits<MultilibSetSerialization> {
     if (M.MultilibVersion.getMinor() > MultilibVersionCurrent.getMinor())
       return "multilib version " + M.MultilibVersion.getAsString() +
              " is unsupported";
+    for (const MultilibSerialization &Lib : M.Multilibs) {
+      if (!Lib.Group.empty()) {
+        bool Found = false;
+        for (const MultilibGroupSerialization &Group : M.Groups)
+          if (Group.Name == Lib.Group) {
+            Found = true;
+            break;
+          }
+        if (!Found)
+          return "multilib \"" + Lib.Dir +
+                 "\" specifies undefined group name \"" + Lib.Group + "\"";
+      }
+    }
     return std::string{};
   }
 };
 
 LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibSerialization)
+LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibGroupSerialization)
 LLVM_YAML_IS_SEQUENCE_VECTOR(MultilibSet::FlagMatcher)
 
 llvm::ErrorOr<MultilibSet>
@@ -214,7 +298,11 @@ MultilibSet::parseYaml(llvm::MemoryBufferRef Input,
     std::string Dir;
     if (M.Dir != ".")
       Dir = "/" + M.Dir;
-    Multilibs.emplace_back(Dir, Dir, Dir, M.Flags);
+    // We transfer M.Group straight into the ExclusiveGroup parameter for the
+    // Multilib constructor. If we later support more than one type of group,
+    // we'll have to look up the group name in MS.Groups, check its type, and
+    // decide what to do here.
+    Multilibs.emplace_back(Dir, Dir, Dir, M.Flags, M.Group);
   }
 
   return MultilibSet(std::move(Multilibs), std::move(MS.FlagMatchers));

clang/test/Driver/baremetal-multilib-exclusive-group.yaml

@@ -0,0 +1,79 @@
+# UNSUPPORTED: system-windows
+
+# RUN: rm -rf %t
+
+# RUN: mkdir -p %t/baremetal_multilib/bin
+# RUN: ln -s %clang %t/baremetal_multilib/bin/clang
+
+# RUN: mkdir -p %t/baremetal_multilib/lib/clang-runtimes
+# RUN: ln -s %s %t/baremetal_multilib/lib/clang-runtimes/multilib.yaml
+
+# RUN: %t/baremetal_multilib/bin/clang -no-canonical-prefixes -x c++ %s -### -o %t.out --target=thumbv7em-none-unknown-eabi --sysroot= 2>%t.err
+
+# RUN: FileCheck -DSYSROOT=%t/baremetal_multilib %s < %t.err --check-prefix=POS
+# RUN: FileCheck -DSYSROOT=%t/baremetal_multilib %s < %t.err --check-prefix=NEG
+
+# Expected results:
+#
+# Due to the Mappings section, all six of these library directories should
+# match the command-line flag --target=thumbv7em-none-unknown-eabi.
+#
+# The two "non_exclusive" directories, which don't have an ExclusiveGroup at
+# all, should both be selected. So should the two "own_group", each of which
+# specifies a different value of ExclusiveGroup. But the three "exclusive",
+# which have the _same_ ExclusiveGroup value, should not: the third one wins.
+# So we expect five of these seven directories to show up in the clang-cc1
+# command line, but not testdir1_exclusive or testdir2_exclusive.
+
+# POS-DAG: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/testdir1_non_exclusive/include/c++/v1"
+# POS-DAG: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/testdir2_non_exclusive/include/c++/v1"
+# POS-DAG: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/testdir3_exclusive/include/c++/v1"
+# POS-DAG: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/testdir1_own_group/include/c++/v1"
+# POS-DAG: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/testdir2_own_group/include/c++/v1"
+
+# NEG-NOT: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/testdir1_exclusive/include/c++/v1"
+# NEG-NOT: "-internal-isystem" "[[SYSROOT]]/bin/../lib/clang-runtimes/testdir2_exclusive/include/c++/v1"
+
+---
+MultilibVersion: 1.0
+
+Groups:
+- Name: actually_exclude_something
+  Type: Exclusive
+
+- Name: foo
+  Type: Exclusive
+
+- Name: bar
+  Type: Exclusive
+
+Variants:
+- Dir: testdir1_non_exclusive
+  Flags: [--target=thumbv7m-none-unknown-eabi]
+
+- Dir: testdir2_non_exclusive
+  Flags: [--target=thumbv7em-none-unknown-eabi]
+
+- Dir: testdir1_exclusive
+  Flags: [--target=thumbv7m-none-unknown-eabi]
+  Group: actually_exclude_something
+
+- Dir: testdir2_exclusive
+  Flags: [--target=thumbv7em-none-unknown-eabi]
+  Group: actually_exclude_something
+
+- Dir: testdir3_exclusive
+  Flags: [--target=thumbv7em-none-unknown-eabi]
+  Group: actually_exclude_something
+
+- Dir: testdir1_own_group
+  Flags: [--target=thumbv7m-none-unknown-eabi]
+  Group: foo
+
+- Dir: testdir2_own_group
+  Flags: [--target=thumbv7em-none-unknown-eabi]
+  Group: bar
+
+Mappings:
+- Match: --target=thumbv7em-none-unknown-eabi
+  Flags: [--target=thumbv7m-none-unknown-eabi]

clang/test/Driver/baremetal-multilib-group-error.yaml

@@ -0,0 +1,27 @@
+# UNSUPPORTED: system-windows
+
+# RUN: rm -rf %t
+
+# RUN: mkdir -p %t/baremetal_multilib/bin
+# RUN: ln -s %clang %t/baremetal_multilib/bin/clang
+
+# RUN: mkdir -p %t/baremetal_multilib/lib/clang-runtimes
+# RUN: ln -s %s %t/baremetal_multilib/lib/clang-runtimes/multilib.yaml
+
+# RUN: %t/baremetal_multilib/bin/clang -no-canonical-prefixes -x c++ %s -### -o %t.out --target=thumbv7em-none-unknown-eabi --sysroot= 2>%t.err
+# RUN: FileCheck %s < %t.err
+
+---
+MultilibVersion: 1.0
+
+Groups:
+- Name: group1
+  Type: Nonsense
+
+Variants:
+- Dir: testdir1
+  Flags: [--target=thumbv7m-none-unknown-eabi]
+  Group: nonexistent_group_name
+
+# CHECK: error: unknown enumerated scalar
+# CHECK: error: multilib "testdir1" specifies undefined group name "nonexistent_group_name"