MIR Parser: Report an error when a machine function doesn't have a corresponding function in the LLVM IR.

[arphaman]

Summary

This patch reports an error when a machine function in the MIR file that has LLVM IR can't find a function with the same name in the loaded LLVM IR module.

llvm/trunk/lib/CodeGen/MIRParser/MIRParser.cpp

if (In.error())
     return true;
   auto FunctionName = MF->Name;
   if (Functions.find(FunctionName) != Functions.end())
     return error(Twine("redefinition of machine function '") + FunctionName +
                  "'");
   Functions.insert(std::make_pair(FunctionName, std::move(MF)));
   if (NoLLVMIR)
     createDummyFunction(FunctionName, M);
+  else if (!M.getFunction(FunctionName))
+    return error(Twine("function '") + FunctionName +
+                 "' isn't defined in the provided LLVM IR");
   return false;
 }
 
 void MIRParserImpl::createDummyFunction(StringRef Name, Module &M) {
   auto &Context = M.getContext();
   Function *F = cast<Function>(M.getOrInsertFunction(
       Name, FunctionType::get(Type::getVoidTy(Context), false)));
   BasicBlock *BB = BasicBlock::Create(Context, "entry", F);

llvm/trunk/test/CodeGen/MIR/machine-function-missing-function.mir

+# RUN: not llc -start-after branch-folder -stop-after branch-folder -o /dev/null %s 2>&1 | FileCheck %s
+# This test ensures that an error is reported when the mir file has LLVM IR and
+# one of the machine functions has a name that doesn't match any function in
+# the LLVM IR.
+
+--- |
+
+  define i32 @foo() {
+    ret i32 0
+  }
+
+...
+---
+name:            foo
+...
+---
+# CHECK: function 'faa' isn't defined in the provided LLVM IR
+name:            faa
+...