[PATCH] D33245: Simplify the use of CVTypeVisitor

[Zachary Turner via Phabricator via llvm-commits]

zturner created this revision.

Similar to https://reviews.llvm.org/D33229, this patch is aimed at reducing boilerplate and simplifying usage.

The problem I'm trying to address here is that there is often a lot of code required to visit a type stream, or even a single record.  You have to create a visitation pipeline.  Then you have to stick a bunch of visitors in it.  Then you have to invoke the right method on the pipeline.  This is usually between 3 and 6 lines of code, with at least 3 different objects in play.  But one of the most common usages is that you have a sequence of bytes, and you want to visit them as deserialized records.  In order to make this work, you have to create a `TypeVisitorCallbackPipeline` and then put a `TypeDeserializer` on it to deserialize the records, and only then can you add your real callbacks to the visitation pipeline.

Since this is such a common use case, it would be nice if it were automatic.  But we don't always want to deserialize records first.  We might not even **have** any record data to deserialize in the first place (think Yaml -> PDB where we have Yaml describing the records, not bytes).  So it can't be required.

At the same time, there is no fundamental reason why `CVTypeVisitor` has to be an object.  It just happens to be one.  We could just invoke a free free function and pass the visitor into the free function instead of constructing a `CVTypeVisitor` with one.

So this patch does all of the above.  After this patch, the following code:

  if (IO.outputting()) {
    codeview::TypeDeserializer Deserializer;
  
    codeview::TypeVisitorCallbackPipeline Pipeline;
    Pipeline.addCallbackToPipeline(Deserializer);
    Pipeline.addCallbackToPipeline(Context.Dumper);
  
    codeview::CVTypeVisitor Visitor(Pipeline);
    consumeError(Visitor.visitTypeRecord(Record));
  }

turns into this:

  if (IO.outputting())
    consumeError(codeview::visitTypeRecord(Record, Context.Dumper));


https://reviews.llvm.org/D33245

Files:
  llvm/include/llvm/DebugInfo/CodeView/CVTypeVisitor.h
  llvm/include/llvm/DebugInfo/CodeView/RandomAccessTypeVisitor.h
  llvm/include/llvm/DebugInfo/PDB/Native/TpiStream.h
  llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
  llvm/lib/DebugInfo/CodeView/CVTypeDumper.cpp
  llvm/lib/DebugInfo/CodeView/CVTypeVisitor.cpp
  llvm/lib/DebugInfo/CodeView/RandomAccessTypeVisitor.cpp
  llvm/lib/DebugInfo/CodeView/TypeDumpVisitor.cpp
  llvm/lib/DebugInfo/CodeView/TypeStreamMerger.cpp
  llvm/lib/DebugInfo/PDB/Native/PDBTypeServerHandler.cpp
  llvm/tools/llvm-pdbdump/Analyze.cpp
  llvm/tools/llvm-pdbdump/LLVMOutputStyle.cpp
  llvm/tools/llvm-pdbdump/PdbYaml.cpp
  llvm/tools/llvm-pdbdump/YamlTypeDumper.cpp
  llvm/unittests/DebugInfo/CodeView/RandomAccessVisitorTest.cpp
  llvm/unittests/DebugInfo/PDB/TypeServerHandlerTest.cpp

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D33245.99163.patch
Type: text/x-patch
Size: 27821 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170516/e98e94c4/attachment-0001.bin>