[PATCH] D38473: Include getting generated struct offsets in CodegenABITypes

[Michael Ferguson via cfe-commits]

I forgot to include the Phabricator URL for the patch in question. It is here:

https://reviews.llvm.org/D38473

Thanks,

-michael

On Mon, Oct 2, 2017 at 3:19 PM, Michael Ferguson <mpfergu at gmail.com> wrote:
> This change adds a new function, CodeGen::getFieldNumber, that
> enables a user of clang's code generation to get the field number
> in a generated LLVM IR struct that corresponds to a particular field
> in a C struct.
>
> It is important to expose this information in Clang's code generation
> interface because there is no reasonable way for users of Clang's code
> generation to get this information. In particular:
>
> 1. LLVM struct types do not include field names.
> 2. Clang adds a non-trivial amount of logic to the code generation of
> LLVM IR types for structs, in particular to handle padding and bit
> fields.
>
> This in some ways is a philosophical continuation of
> https://reviews.llvm.org/D35180 .
>
> I'm working on a programming language that uses Clang to create
> seamless C interoperability. One of the language features is to create
> "extern records", which are just structs that have a definition in C
> code. The language needs to be able to code generate element access to
> particular structure fields by name, and without this patch, I need to
> use clang-internal headers to do so.
>
>
>
> diff --git a/include/clang/CodeGen/CodeGenABITypes.h
> b/include/clang/CodeGen/CodeGenABITypes.h
> index 615e55c8b6..f4fa28da1b 100644
> --- a/include/clang/CodeGen/CodeGenABITypes.h
> +++ b/include/clang/CodeGen/CodeGenABITypes.h
> @@ -78,6 +78,10 @@ llvm::FunctionType
> *convertFreeFunctionType(CodeGenModule &CGM,
>
>  llvm::Type *convertTypeForMemory(CodeGenModule &CGM, QualType T);
>
> +// Returns a field number for a struct suitable for GEP'ing
> +unsigned getFieldNumber(CodeGenModule &CGM,
> +                        const RecordDecl *RD, const FieldDecl *FD);
> +
>  }  // end namespace CodeGen
>  }  // end namespace clang
>
> diff --git a/lib/CodeGen/CodeGenABITypes.cpp b/lib/CodeGen/CodeGenABITypes.cpp
> index 0735a9c3df..759ad75897 100644
> --- a/lib/CodeGen/CodeGenABITypes.cpp
> +++ b/lib/CodeGen/CodeGenABITypes.cpp
> @@ -17,6 +17,7 @@
>  //===----------------------------------------------------------------------===//
>
>  #include "clang/CodeGen/CodeGenABITypes.h"
> +#include "CGRecordLayout.h"
>  #include "CodeGenModule.h"
>  #include "clang/CodeGen/CGFunctionInfo.h"
>  #include "clang/Frontend/CodeGenOptions.h"
> @@ -80,3 +81,8 @@ llvm::Type *
>  CodeGen::convertTypeForMemory(CodeGenModule &CGM, QualType T) {
>    return CGM.getTypes().ConvertTypeForMem(T);
>  }
> +
> +unsigned CodeGen::getFieldNumber(CodeGenModule &CGM,
> +                                 const RecordDecl *RD, const FieldDecl *FD) {
> +  return CGM.getTypes().getCGRecordLayout(RD).getLLVMFieldNo(FD);
> +}