[Orc] Allow in-band errors for runAsMain() via SPS

[sgraenitz]

Summary

runAsMain() may fail for function-specific reasons (e.g. provided pointer to main is invalid). There should be a way to propagate such in-band errors back to the controller.

[sgraenitz]

Passing a valid function address is the responsibility of the user and laying out argv correctly is an ABI detail. If anything like this fails, we probably have to hang up anyway and send the error with that D111527.

llvm/include/llvm/ExecutionEngine/Orc/Shared/OrcRTBridge.h

 using SPSSimpleExecutorMemoryManagerReserveSignature =
     shared::SPSExpected<shared::SPSExecutorAddr>(shared::SPSExecutorAddr,
                                                  uint64_t);
 using SPSSimpleExecutorMemoryManagerFinalizeSignature =
     shared::SPSError(shared::SPSExecutorAddr, shared::SPSFinalizeRequest);
 using SPSSimpleExecutorMemoryManagerDeallocateSignature = shared::SPSError(
     shared::SPSExecutorAddr, shared::SPSSequence<shared::SPSExecutorAddr>);
 
-using SPSRunAsMainSignature = int64_t(shared::SPSExecutorAddr,
-                                      shared::SPSSequence<shared::SPSString>);
+using SPSRunAsMainSignature = shared::SPSExpected<int64_t>(
+    shared::SPSExecutorAddr, shared::SPSSequence<shared::SPSString>);
 
 } // end namespace rt
 } // end namespace orc
 } // end namespace llvm
 
 #endif // LLVM_EXECUTIONENGINE_ORC_SHARED_ORCRTBRIDGE_H

llvm/lib/ExecutionEngine/Orc/SimpleRemoteEPC.cpp

for (auto &Element : Request) {
     } else
       return R.takeError();
   }
   return std::move(Result);
 }
 
 Expected<int32_t> SimpleRemoteEPC::runAsMain(ExecutorAddr MainFnAddr,
                                              ArrayRef<std::string> Args) {
-  int64_t Result = 0;
+  Expected<int64_t> Result(0);
   if (auto Err = callSPSWrapper<rt::SPSRunAsMainSignature>(
           RunAsMainAddr, Result, ExecutorAddr(MainFnAddr), Args))
     return std::move(Err);
   return Result;
 }
 
 void SimpleRemoteEPC::callWrapperAsync(ExecutorAddr WrapperFnAddr,
                                        IncomingWFRHandler OnComplete,

llvm/lib/ExecutionEngine/Orc/TargetProcess/OrcRTBootstrap.cpp

return WrapperFunction<void(SPSSequence<SPSMemoryAccessBufferWrite>)>::handle(
       .release();
 }
 
 static llvm::orc::shared::detail::CWrapperFunctionResult
 runAsMainWrapper(const char *ArgData, size_t ArgSize) {
   return WrapperFunction<rt::SPSRunAsMainSignature>::handle(
              ArgData, ArgSize,
              [](ExecutorAddr MainAddr,
-                std::vector<std::string> Args) -> int64_t {
+                std::vector<std::string> Args) -> Expected<int64_t> {
                return runAsMain(MainAddr.toPtr<int (*)(int, char *[])>(), Args);
              })
       .release();
 }
 
 void addTo(StringMap<ExecutorAddr> &M) {
   M[rt::MemoryWriteUInt8sWrapperName] = ExecutorAddr::fromPtr(
       &writeUIntsWrapper<tpctypes::UInt8Write,