[LLVMdev] Data Dependence Graph

Misha Brukman brukman at cs.uiuc.edu
Fri Aug 12 06:51:13 PDT 2005

On Fri, Aug 12, 2005 at 01:16:39PM -0500, Manvi Agarwal wrote:
> Is it possible to generate a data dependence graph of llvm assembly
> file?

I am not aware of a general framework for data dependence analysis in
LLVM.  It's been talked about, but hasn't (yet) been implemented.

> How can I get the data flow information in X.ll file? 

LLVM assembly is in SSA, data flow (use-def and def-use chains) is
explicit.  What exactly are you looking for?

> Also, in .ll file I see everyline ends with something like this:
> <type> [#uses=3] What is the significance of this and is it used
> anyway by the compiler for data dependence analysis.

Since it follows the semicolon ';' it's an LLVM comment and ignored by
llvm-as and gccas.  However, it's not any extra information -- LLVM is
fully-typed so the <type> is the type of the statement on the line it
appears, and since def-use chains are explicit in LLVM (see above), the
# uses is also explicit in the code, so it's not any extra information
that isn't present already, either.

This paper is a good introduction to LLVM:

Misha Brukman :: http://misha.brukman.net :: http://llvm.cs.uiuc.edu

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