[llvm] r263275 - [ThinLTO] Support for reference graph in per-module and combined summary.

[Duncan P. N. Exon Smith via llvm-commits]

> On 2016-Mar-21, at 08:48, Xinliang David Li <xinliangli at gmail.com> wrote:
> 
> 
> This is guarded under PGO flag only.
> 
> PGO and -flto=thin
>  
>  
> 
> I'm pretty surprised to see these here.
> 
> This is unfortunate  -- the block level profile count information is discarded and we need to use BFI to reconstruct it.  One way to remove this dependency  is to use new analysis pass to annotate callsites with profile count meta data.
> 
> Is this new analysis pass currently available? If so, can you point me to it? The above code was used in other locations in the compiler that needed similar info.
> 
> 
> No -- not I am aware of.  I was just suggesting if it is considered a problem, this is one way to solve it.
> 

I think somehow running a pass *before* writing out the bitcode would
be better.  I'm not sure attaching something to the calls is the best
way, or if Mehdi's idea to generate a FunctionIndex that's passed in
to the bitcode reader makes more sense.

Or, maybe the FunctionIndex should be attached to the Module?

> David
> 
>  
> 
> Thanks,
> Teresa
>  
> 
> David
>  
> 
> 
> 
> > +  }
> > +
> >   Stream.EnterSubblock(bitc::FUNCTION_BLOCK_ID, 4);
> >   VE.incorporateFunction(F);
> 
> 
> > Modified: llvm/trunk/lib/Bitcode/Writer/LLVMBuild.txt
> > URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Bitcode/Writer/LLVMBuild.txt?rev=263275&r1=263274&r2=263275&view=diff
> > ==============================================================================
> > --- llvm/trunk/lib/Bitcode/Writer/LLVMBuild.txt (original)
> > +++ llvm/trunk/lib/Bitcode/Writer/LLVMBuild.txt Fri Mar 11 12:52:24 2016
> > @@ -19,4 +19,4 @@
> > type = Library
> > name = BitWriter
> > parent = Bitcode
> > -required_libraries = Core Support
> > +required_libraries = Analysis Core Support
> 
> This means that `llvm-as` now has a dependency on lib/Analysis... which
> is surprising.
> 
> I feel like we've done something fundamentally wrong if we have to
> run expensive analyses in order to write out IR.
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
> 
> 
> 
> 
> -- 
> Teresa Johnson |	 Software Engineer |	 tejohnson at google.com |	 408-460-2413