[ORC] Provide default MemoryAccess in SimpleRemoteEPC, add WritePointers impl.

Make EPCGenericMemoryAccess the default implementation for the MemoryAccess
object in SimpleRemoteEPC, and add support for the WritePointers operation to
OrcTargetProcess (previously this operation was unimplemented and would have
triggered an error if accessed in a remote-JIT setup).

No testcase yet: This functionality requires cross-process JITing to test (or a
much more elaborate unit-test setup). It can be tested once the new top-level
ORC runtime project lands.

Author: lhames

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

@@ -42,6 +42,7 @@ extern const char *MemoryWriteUInt16sWrapperName;
 extern const char *MemoryWriteUInt32sWrapperName;
 extern const char *MemoryWriteUInt64sWrapperName;
 extern const char *MemoryWriteBuffersWrapperName;
+extern const char *MemoryWritePointersWrapperName;
 
 extern const char *RegisterEHFrameSectionWrapperName;
 extern const char *DeregisterEHFrameSectionWrapperName;

llvm/lib/ExecutionEngine/Orc/Shared/OrcRTBridge.cpp

@@ -49,6 +49,8 @@ const char *MemoryWriteUInt64sWrapperName =
     "__llvm_orc_bootstrap_mem_write_uint64s_wrapper";
 const char *MemoryWriteBuffersWrapperName =
     "__llvm_orc_bootstrap_mem_write_buffers_wrapper";
+const char *MemoryWritePointersWrapperName =
+    "__llvm_orc_bootstrap_mem_write_pointers_wrapper";
 
 const char *RegisterEHFrameSectionWrapperName =
     "llvm_orc_registerEHFrameSectionWrapper";

llvm/lib/ExecutionEngine/Orc/SimpleRemoteEPC.cpp

@@ -227,7 +227,17 @@ SimpleRemoteEPC::createDefaultMemoryManager(SimpleRemoteEPC &SREPC) {
 
 Expected<std::unique_ptr<ExecutorProcessControl::MemoryAccess>>
 SimpleRemoteEPC::createDefaultMemoryAccess(SimpleRemoteEPC &SREPC) {
-  return nullptr;
+  EPCGenericMemoryAccess::FuncAddrs FAs;
+  if (auto Err = SREPC.getBootstrapSymbols(
+          {{FAs.WriteUInt8s, rt::MemoryWriteUInt8sWrapperName},
+           {FAs.WriteUInt16s, rt::MemoryWriteUInt16sWrapperName},
+           {FAs.WriteUInt32s, rt::MemoryWriteUInt32sWrapperName},
+           {FAs.WriteUInt64s, rt::MemoryWriteUInt64sWrapperName},
+           {FAs.WriteBuffers, rt::MemoryWriteBuffersWrapperName},
+           {FAs.WritePointers, rt::MemoryWritePointersWrapperName}}))
+    return std::move(Err);
+
+  return std::make_unique<EPCGenericMemoryAccess>(SREPC, FAs);
 }
 
 Error SimpleRemoteEPC::sendMessage(SimpleRemoteEPCOpcode OpC, uint64_t SeqNo,

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

@@ -45,6 +45,18 @@ writeBuffersWrapper(const char *ArgData, size_t ArgSize) {
       .release();
 }
 
+static llvm::orc::shared::CWrapperFunctionResult
+writePointersWrapper(const char *ArgData, size_t ArgSize) {
+  return WrapperFunction<void(SPSSequence<SPSMemoryAccessPointerWrite>)>::
+      handle(ArgData, ArgSize,
+             [](std::vector<tpctypes::PointerWrite> Ws) {
+               for (auto &W : Ws)
+                 *W.Addr.template toPtr<void **>() =
+                     W.Value.template toPtr<void *>();
+             })
+          .release();
+}
+
 static llvm::orc::shared::CWrapperFunctionResult
 runAsMainWrapper(const char *ArgData, size_t ArgSize) {
   return WrapperFunction<rt::SPSRunAsMainSignature>::handle(
@@ -92,6 +104,8 @@ void addTo(StringMap<ExecutorAddr> &M) {
                          shared::SPSMemoryAccessUInt64Write>);
   M[rt::MemoryWriteBuffersWrapperName] =
       ExecutorAddr::fromPtr(&writeBuffersWrapper);
+  M[rt::MemoryWritePointersWrapperName] =
+      ExecutorAddr::fromPtr(&writePointersWrapper);
   M[rt::RegisterEHFrameSectionWrapperName] =
       ExecutorAddr::fromPtr(&llvm_orc_registerEHFrameSectionWrapper);
   M[rt::DeregisterEHFrameSectionWrapperName] =