[llvm-dev] [Help] Add custom pragma

[Vedant Kumar via llvm-dev]

That file is generated by the clang-tblgen tool:

  COMMAND = cd /Users/vk/Desktop/llvm/DA-NoModules/tools/clang/include/clang/Sema && /Users/vk/Desktop/llvm/DA-NoModules/bin/clang-tblgen -gen-clang-attr-parsed-attr-list -I /Users/vk/Desktop/llvm/tools/clang/include/clang/Sema/../../ -I /Users/vk/Desktop/llvm/tools/clang/include/clang/Sema -I /Users/vk/Desktop/llvm/lib/Target -I /Users/vk/Desktop/llvm/include /Users/vk/Desktop/llvm/tools/clang/include/clang/Sema/../Basic/Attr.td -o /Users/vk/Desktop/llvm/DA-NoModules/tools/clang/include/clang/Sema/AttrParsedAttrList.inc.tmp

Try looking include/clang/Basic/Attr.td?

best,
vedant

> On Oct 25, 2016, at 2:54 PM, Sunghyun Park via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi, all. 
> I want to give programmer ability to tell LLVM that certain region of code is expected to get specialized optimization.
> So, I'm trying to make custom pragma to mark certain region of code and pass this information to LLVM, in the similar way that '#pragma clang loop unroll_count(N)' works.
> 
> By tracking the framework of loop unroll pragma, I found out it works in the way below. 
> (1) Detect pragma at lexer, parser. 
> (2) Create AttributeList and push it into AST.
> (3) Once AST is built, consume AST and generate LLVM IR at CodeGeneration
> (4) If attribute for loop unroll is found, put tag on LLVM IR with Meta data which indicates whether to unroll loop.
> 
> Now I can detect my own pragma and figured it out how to create and tag custom metadata.
> The problem is that creating custom AttributeList is somewhat hard to follow. 
> 
> As far as I know, the attribute for loop unroll pragma gets serviced at ProcessSmtAttrbute Function @ tools/clang/lib/Sema/SemaStmtAttr.cpp.
> It contains switch statement like below.
> 
> ProcessSmtAttrbute @ tools/clang/lib/Sema/SemaStmtAttr.cpp
> // A : AttributeList - passed by argument
> switch( A.getKind() ) {
>   case AttributeList::UnknownAttribute:
>     ~
>   case AttributeList::AT_FallThrough:
>     return ~
>   case AttributeList::AT_LoopHint: 
>     return handleLoopHintAttr( ~ )
>   case AttributeList::AT_OpenCLUnrollHint:
>   ~
>   ...
> }
> 
> As I want to define new attribute, I've tried to find where the definitions for AT_LoopHint, AT_FallThrough are done. This is what I found.
> 
> class AttributeList @ tools/clang/include/clang/Sema/AttributeList.h
> 
> enum Kind{
>    #define PARSED ATTR(NAME) AT_##NAME,
>    #include "clang/Sema/AttrParsedAttrList.inc"
>    #undef PARSED_ATTR
>    IgnoredAttribute,
>    UnkownAttribute
> };
> 
> It looks like those are defined at this enum, but there's no such file, "clang/Sema/AttrParsedAttrList.inc".
> 
> Anyone knows how those definitions are defined and how the kind of attributes are decided?
> Thank you for your valuable time!
> 
> -- 
> Best, Sung
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