Request and run trivial function

Author: weliveindetail

JitFromScratch.cpp

@@ -20,3 +20,16 @@ Error JitFromScratch::submitModule(std::unique_ptr<Module> M,
   LLVM_DEBUG(dbgs() << "Submit IR module:\n\n" << *M << "\n\n");
   return LLJIT->addIRModule(ThreadSafeModule(std::move(M), std::move(C)));
 }
+
+Expected<JITTargetAddress> JitFromScratch::getFunctionAddr(StringRef Name) {
+  Expected<JITEvaluatedSymbol> S = LLJIT->lookup(Name);
+  if (!S)
+    return S.takeError();
+
+  JITTargetAddress A = S->getAddress();
+  if (!A)
+    return createStringError(inconvertibleErrorCode(),
+                             "'%s' evaluated to nullptr", Name.data());
+
+  return A;
+}

JitFromScratch.h

@@ -1,12 +1,15 @@
 #pragma once
 
+#include <llvm/ADT/StringRef.h>
 #include <llvm/ADT/Triple.h>
+#include <llvm/ExecutionEngine/JITSymbol.h>
 #include <llvm/ExecutionEngine/Orc/LLJIT.h>
 #include <llvm/IR/DataLayout.h>
 #include <llvm/IR/LLVMContext.h>
 #include <llvm/IR/Module.h>
 #include <llvm/Support/Error.h>
 
+#include <functional>
 #include <memory>
 
 class JitFromScratch {
@@ -29,7 +32,19 @@ class JitFromScratch {
 
   llvm::Error submitModule(std::unique_ptr<llvm::Module> M,
                            std::unique_ptr<llvm::LLVMContext> C);
+
+  template <class Signature_t>
+  llvm::Expected<std::function<Signature_t>> getFunction(llvm::StringRef Name) {
+    if (auto A = getFunctionAddr(Name))
+      return std::function<Signature_t>(
+          llvm::jitTargetAddressToPointer<Signature_t *>(*A));
+    else
+      return A.takeError();
+  }
+
 private:
   std::unique_ptr<llvm::orc::LLJIT> LLJIT;
   llvm::Triple TT;
+
+  llvm::Expected<llvm::JITTargetAddress> getFunctionAddr(llvm::StringRef Name);
 };

main.cpp

@@ -109,10 +109,14 @@ int main(int argc, char **argv) {
   auto M = std::make_unique<Module>("JitFromScratch", *C);
   M->setDataLayout(Jit.getDataLayout());
 
-  ExitOnErr(codegenIR(*M, arrayElements(x)));
+  std::string JitedFnName = ExitOnErr(codegenIR(*M, arrayElements(x)));
   ExitOnErr(Jit.submitModule(std::move(M), std::move(C)));
 
+  // Request function; this compiles to machine code and links.
+  auto getZero = ExitOnErr(Jit.getFunction<int(int, int)>(JitedFnName));
+
   int *z = integerDistances(x, y);
+  z[1] = getZero(0, 0);
 
   outs() << format("Integer Distances: %d, %d, %d\n\n", z[0], z[1], z[2]);
   outs().flush();