[ORC] Add a method to JITTargetMachineBuilder to get the default data layout

for the target machine.

This simplifies usage during setup of concurrent JIT stacks where the client
needs a DataLayout, but not a TargetMachine (TargetMachines are created on
the fly by the compile threads later).

llvm-svn: 343429

include/llvm/ExecutionEngine/Orc/JITTargetMachineBuilder.h

@@ -56,6 +56,18 @@ public:
   /// also be registered.
   Expected<std::unique_ptr<TargetMachine>> createTargetMachine();
 
+  /// Get the default DataLayout for the target.
+  ///
+  /// Note: This is reasonably expensive, as it creates a temporary
+  /// TargetMachine instance under the hood. It is only suitable for use during
+  /// JIT setup.
+  Expected<DataLayout> getDefaultDataLayoutForTarget() {
+    auto TM = createTargetMachine();
+    if (!TM)
+      return TM.takeError();
+    return (*TM)->createDataLayout();
+  }
+
   /// Set the CPU string.
   JITTargetMachineBuilder &setCPU(std::string CPU) {
     this->CPU = std::move(CPU);

tools/lli/lli.cpp

@@ -786,12 +786,7 @@ int runOrcLazyJIT(const char *ProgName) {
                         ? Optional<CodeModel::Model>(CMModel)
                         : None);
 
-  DataLayout DL("");
-  {
-    // Create a throwaway TargetMachine to get the data layout.
-    auto TM = ExitOnErr(JTMB.createTargetMachine());
-    DL = TM->createDataLayout();
-  }
+  DataLayout DL = ExitOnErr(JTMB.getDefaultDataLayoutForTarget());
   auto J = ExitOnErr(orc::LLLazyJIT::Create(std::move(JTMB), DL, LazyJITCompileThreads));
 
   if (PerModuleLazy)