[cfe-dev] Emitting loop metadata in codegen - pragmas, annotations

[ihusar at fit.vutbr.cz]

Hello,


    I am writing here a solution to the pragmas and annotating code:

    I found Paul's patch at

http://lists.cs.uiuc.edu/pipermail/cfe-dev/2013-March/028366.html

and it provides a nice guidelines for adding new pragmas with metadata.
However metadatas have
I then handled code annotation with this code in CGStmt.cpp

void CodeGenFunction::EmitAttributedStmt(const AttributedStmt &S) {

   bool generateAnnotation = false;

   typedef ArrayRef<const Attr*> AttrList;
   AttrList Attrs = S.getAttrs();
   for (AttrList::iterator I = Attrs.begin(), IE = Attrs.end(); I != IE;  
++I) {
     if (isa<MyAttr>(*I)) {
     	generateAnnotation = true;
     }
   }

   if (generateAnnotation)
   {
	  llvm::Value *Args[4] = {
	    Builder.CreateBitCast(CGM.EmitAnnotationString("str1"), Int8PtrTy),
	    Builder.CreateBitCast(CGM.EmitAnnotationString("pragma_begin"),  
Int8PtrTy),
	    Builder.CreateBitCast(CGM.EmitAnnotationUnit(S.getLocStart()),  
Int8PtrTy),
	    CGM.EmitAnnotationLineNo(S.getLocStart())
	  };
	  llvm::Value *V =  
Builder.CreateCall(CGM.getIntrinsic(llvm::Intrinsic::var_annotation),  
Args);
   }


   EmitStmt(S.getSubStmt());
   ...

}

This the generates annotation intrinsics that are kept by opt at the  
original place
(unlike metadata).

call void @llvm.var.annotation(...

I hope these annotations won't make any optimizations weaker, but in the  
LLVM IR documetation is written that they are
ignored by opt.

Best regards
     Adam


On Tue, 03 Sep 2013 17:03:25 +0200, ihusar at fit.vutbr.cz
<ihusar at fit.vutbr.cz> wrote:

> Dear Paul and others,
>
>    I would like to ask whether you made any progress with this,
> we are actually trying to do a similar thing:
>
> - One thing is to introduce ICC-like pragmas and add support for them in  
> the vectorizer
>    (in fact this seems like the thing you were doing).
> - Second one is to identify a block of code that should be identified as  
> an
>    instruction set extension (ISE) and automatically generate a
>    description for an ADL Codal used in Codasip Framework.
>
> I successfully added some pragmas to the clang, but currently I am  
> trying to figure out how to
> correctly store metadata.
>
> Do you have some clues i could follow? E.g. if the code is not private  
> to Intel, could I take a look?:)
>
> Thank you and best regards
>    Adam
>
>
>
>
> On Fri, 22 Feb 2013 21:50:57 +0100, Redmond, Paul  
> <paul.redmond at intel.com> wrote:
>
>> Hi,
>>
>> As discussed earlier I'm implementing #pragma ivdep in clang. I use  
>> AttributedStmt with an IVDepAttr to wrap loop Stmts in the AST. So far  
>> I have only hacked in codegen to attach loop metadata.
>>
>> To do this correctly I need to attach metadata to all predecessors of  
>> the loop header. Also, I need to attach metadata to all loads and  
>> stores in the loop. (see llvm.loop.parallel and  
>> llvm.mem.parallel_loop_access)
>>
>> I'm wondering what the best way to implement this in clang codegen? I  
>> think this could get really messy and become very fragile if I just  
>> start modifying EmitForStmt, etc to check for some flag.
>>
>> One idea I've been thinking about is creating the metadata after code  
>> emission using a llvm loop pass (living in clang/lib/CodeGen) Basically  
>> during codegen I would attach a simple metadata (clang.pragma.ivdep or  
>> something) to a block in the loop and use the pass to translate to the  
>> metadata understood by llvm. I don't see a precedent for running  
>> clang-specific passes in codegen though..
>>
>> Comments and suggestions are appreciated.
>>
>> paul
>> _______________________________________________
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>> cfe-dev at cs.uiuc.edu
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