[llvm-dev] [Help] Add custom pragma

[Vedant Kumar via llvm-dev]

> Yes. I checked that file, but I wasn't sure whether that is right one to look at. 

It seems promising. I imagine you'd want something like the LoopHint attr.

> What is *.td extension btw?

The llvm project uses that extension to identify TableGen inputs
(http://llvm.org/docs/TableGen/).

vedant

> On Oct 25, 2016, at 4:12 PM, Sunghyun Park <sunggg at umich.edu> wrote:
> 
> Yes. I checked that file, but I wasn't sure whether that is right one to look at. 
> What is *.td extension btw? When I google it, it says this is for Windows Debug Simulator. 
> Why clang use this extension, which is limited to Windows environment?
> 
> On Tue, Oct 25, 2016 at 7:00 PM, Vedant Kumar <vsk at apple.com> wrote:
> 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
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
> 
> 
> 
> -- 
> Best, Sung