[PATCH] MIR Serialization: Create dummy functions for the parsed machine functions when MIR file doesn't contain LLVM IR.

[Duncan P. N. Exon Smith]

> On 2015-May-29, at 11:33, Alex Lorenz <arphaman at gmail.com> wrote:
> 
> Hi dexonsmith, bogner, bob.wilson,
> 
> This patch is based on the patch that connects MIRParser to the machine function analysis pass (http://reviews.llvm.org/D9928).
> 
> This patch creates dummy LLVM functions with one basic block and a return instruction for the parsed machine functions when the MIR file doesn't include LLVM IR.
> This is needed as the machine function analysis pass creates machine functions only for the functions defined in the current LLVM module.
> 
> REPOSITORY
>  rL LLVM
> 
> http://reviews.llvm.org/D10135
> 
> Files:
>  lib/CodeGen/MIRParser/MIRParser.cpp
>  test/CodeGen/MIR/llvmIRMissing.mir
> 
I'm skeptical that testcases without backing LLVM IR are going to prove
useful.  This particular patch doesn't seem to be too complicated, so
I'm fine with it, but I think you should focus on serializing MIR that
*has* matching LLVM IR.

A few comments below; otherwise LGTM.

> Index: lib/CodeGen/MIRParser/MIRParser.cpp
> ===================================================================
> --- lib/CodeGen/MIRParser/MIRParser.cpp
> +++ lib/CodeGen/MIRParser/MIRParser.cpp
> @@ -19,6 +19,7 @@
>  #include "llvm/AsmParser/Parser.h"
>  #include "llvm/CodeGen/MachineFunction.h"
>  #include "llvm/CodeGen/MIRYamlMapping.h"
> +#include "llvm/IR/Instructions.h"
>  #include "llvm/IR/Module.h"
>  #include "llvm/Support/SMLoc.h"
>  #include "llvm/Support/SourceMgr.h"
> @@ -51,13 +52,17 @@
>    /// Parse the machine function in the current YAML document.
>    ///
>    /// Return true if an error occurred.

You should document the effect that `NoLLVMIR` has.

> -  bool parseMachineFunction(yaml::Input &In);
> +  bool parseMachineFunction(yaml::Input &In, Module &M, bool NoLLVMIR);
>  
>    /// Initialize the machine function to the state that's described in the MIR
>    /// file.
>    ///
>    /// Return true if error occurred.
>    bool initializeMachineFunction(MachineFunction &MF, SMDiagnostic &Error);
> +
> +private:
> +  /// Create an empty function with the given name.
> +  void createDummyFunction(StringRef Name, Module &M);
>  };
>  
>  } // end namespace llvm
> @@ -84,6 +89,7 @@
>    }
>  
>    std::unique_ptr<Module> M;
> +  bool NoLLVMIR = false;
>    // Parse the block scalar manually so that we can return unique pointer
>    // without having to go trough YAML traits.
>    if (const auto *BSN =
> @@ -98,28 +104,40 @@
>    } else {
>      // Create an new, empty module.
>      M = llvm::make_unique<Module>(Filename, Context);
> +    NoLLVMIR = true;
>    }
>  
>    // Parse the machine functions.
>    do {
> -    if (parseMachineFunction(In))
> +    if (parseMachineFunction(In, *M, NoLLVMIR))
>        return nullptr;
>      In.nextDocument();
>    } while (In.setCurrentDocument());
>  
>    return M;
>  }
>  
> -bool MIRParserImpl::parseMachineFunction(yaml::Input &In) {
> +bool MIRParserImpl::parseMachineFunction(yaml::Input &In, Module &M,
> +                                         bool NoLLVMIR) {
>    auto MF = llvm::make_unique<yaml::MachineFunction>();
>    yaml::yamlize(In, *MF, false);
>    if (In.error())
>      return true;
>    auto FunctionName = MF->Name;
>    Functions.insert(std::make_pair(FunctionName, std::move(MF)));
> +  if (NoLLVMIR)
> +    createDummyFunction(FunctionName, M);
>    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);
> +  ReturnInst::Create(Context, nullptr, BB);

`unreachable` is a simpler terminator than `ret void`, so I think it
makes more sense in a dummy function.

> +}
> +
>  bool MIRParserImpl::initializeMachineFunction(MachineFunction &MF,
>                                                SMDiagnostic &Error) {
>    auto It = Functions.find(MF.getName());
> Index: test/CodeGen/MIR/llvmIRMissing.mir
> ===================================================================
> --- test/CodeGen/MIR/llvmIRMissing.mir
> +++ test/CodeGen/MIR/llvmIRMissing.mir
> @@ -1,5 +1,7 @@
> -# RUN: llc -start-after branch-folder -stop-after branch-folder -o /dev/null %s
> +# RUN: llc -start-after branch-folder -stop-after branch-folder -o /dev/null %s | FileCheck %s
>  # This test ensures that the MIR parser accepts files without the LLVM IR.
>  
>  ---
> +# CHECK: name: foo
> +name: foo
>  ...
>