[ORC][MachO] Simplify use of LC_BUILD_VERSION in JITDylib headers.

API clients can now set a MachO::HeaderOptions::BuildVersionOpts field to have
MachOPlatform add an LC_BUILD_VERSION load command to the Mach header for each
JITDylib.

No testcase yet. In the future we'll try to add a MachO parser to the ORC
runtime and extra test options to llvm-jitlink for this.

This commit also incidentally fixes a bug in the MachOBuilder class that lead to
a delegation cycle.

Author: Lang Hames

llvm/include/llvm/ExecutionEngine/Orc/MachOBuilder.h

@@ -78,7 +78,7 @@ struct MachOBuilderLoadCommand
 
   template <typename... ArgTs>
   MachOBuilderLoadCommand(ArgTs &&...Args)
-      : MachOBuilderLoadCommand(std::forward<ArgTs>(Args)...) {}
+      : MachOBuilderLoadCommandImplBase<LCType>(std::forward<ArgTs>(Args)...) {}
 };
 
 template <>

llvm/include/llvm/ExecutionEngine/Orc/MachOPlatform.h

@@ -58,9 +58,24 @@ class MachOPlatform : public Platform {
       uint32_t CompatibilityVersion;
     };
 
+    struct BuildVersionOpts {
+
+      // Derive platform from triple.
+      static BuildVersionOpts fromTriple(const Triple &TT, uint32_t MinOS,
+                                         uint32_t SDK);
+
+      uint32_t Platform; // Platform.
+      uint32_t MinOS;    // X.Y.Z is encoded in nibbles xxxx.yy.zz
+      uint32_t SDK;      // X.Y.Z is encoded in nibbles xxxx.yy.zz
+    };
+
     /// Override for LC_IC_DYLIB. If this is nullopt, {JD.getName(), 0, 0, 0}
     /// will be used.
     std::optional<Dylib> IDDylib;
+
+    /// Override for LC_BUILD_VERSION. If this is nullopt then
+    std::optional<BuildVersionOpts> BuildVersion;
+
     /// List of LC_LOAD_DYLIBs.
     std::vector<Dylib> LoadDylibs;
     /// List of LC_RPATHs.

llvm/lib/ExecutionEngine/Orc/MachOPlatform.cpp

@@ -255,6 +255,36 @@ struct ObjCImageInfoFlags {
 namespace llvm {
 namespace orc {
 
+MachOPlatform::HeaderOptions::BuildVersionOpts
+MachOPlatform::HeaderOptions::BuildVersionOpts::fromTriple(const Triple &TT,
+                                                           uint32_t MinOS,
+                                                           uint32_t SDK) {
+
+  uint32_t Platform;
+  switch (TT.getOS()) {
+  case Triple::IOS:
+    Platform = TT.isSimulatorEnvironment() ? MachO::PLATFORM_IOS
+                                           : MachO::PLATFORM_IOSSIMULATOR;
+    break;
+  case Triple::MacOSX:
+    Platform = MachO::PLATFORM_MACOS;
+    break;
+  case Triple::TvOS:
+    Platform = TT.isSimulatorEnvironment() ? MachO::PLATFORM_TVOS
+                                           : MachO::PLATFORM_TVOSSIMULATOR;
+    break;
+  case Triple::WatchOS:
+    Platform = TT.isSimulatorEnvironment() ? MachO::PLATFORM_WATCHOS
+                                           : MachO::PLATFORM_WATCHOSSIMULATOR;
+    break;
+  default:
+    Platform = MachO::PLATFORM_UNKNOWN;
+    break;
+  }
+
+  return {Platform, MinOS, SDK};
+}
+
 Expected<std::unique_ptr<MachOPlatform>> MachOPlatform::Create(
     ExecutionSession &ES, ObjectLinkingLayer &ObjLinkingLayer,
     JITDylib &PlatformJD, std::unique_ptr<DefinitionGenerator> OrcRuntime,
@@ -1695,6 +1725,11 @@ jitlink::Block &createHeaderBlock(MachOPlatform &MOP,
   else
     B.template addLoadCommand<MachO::LC_ID_DYLIB>(JD.getName(), 0, 0, 0);
 
+  if (Opts.BuildVersion)
+    B.template addLoadCommand<MachO::LC_BUILD_VERSION>(
+        Opts.BuildVersion->Platform, Opts.BuildVersion->MinOS,
+        Opts.BuildVersion->SDK, static_cast<uint32_t>(0));
+
   for (auto &D : Opts.LoadDylibs)
     B.template addLoadCommand<MachO::LC_LOAD_DYLIB>(
         D.Name, D.Timestamp, D.CurrentVersion, D.CompatibilityVersion);