[LLVMdev] Conditional Predicate Extraction

Prabhat Kumar Saraswat prabhat.saraswat at gmail.com
Thu Dec 20 00:17:55 PST 2007

Thanks cedric,

 I will look into the ways the debug information could be used.

 However, it seems like i would have to write a piece of code that would
successively reduce the conditional predicate in terms of the local and
global variables (of the code). I plan to do it like this.

Since i am using a runonBasicblock pass, the context information between two
basic blocks cannot be shared, since the pass runs on each basic block at a
time. So the idea is to print the output of the pass into a database (a text
file). This database is then parsed to populate a prefix tree, where the
nodes are the temporary variables and llvm opcodes. This tree would be
consumed to eliminate the temporary variables and replace the opcodes by an
expression in a c like format (infix arithmetic notation ).

Since in the begining of each basic block the local/global variables are
loaded into temporary variables, it is understood that the expression would
be in terms of these local/global variables since the temporary variables
would have been already consumed by the aforementioned process.

How does it sound like? Is it possible for the llvm-gcc to emit the bitcode
in a form which is close to the source language (atleast the variable
names). Are there some optimizations possible ?

Thanks alot


On Dec 19, 2007 7:32 PM, Cédric Venet <cedric.venet at laposte.net> wrote:

> > The questions are:
> > 1. Is it possible to somehow intersperse IR and highlevel code of the
> program (in C or C++).
> > Suggestions and answers are welcome.
> You can probably use debug information (generated by llvm gcc on intrinsic
> form, see MachineModuleInfo.h) to identify the source ligne for a
> condition
> and the relation between the temporary llvm variable and the high level
> language variable.
> Perharps it isn't very reliable but I don't see other solution with llvm.
> (But I am just a novice).
> If you are just doing flow graph analysis, you can consider doing it at
> the
> C/C++ level. Clang (which only support most of C at the moment) as a
> little
> framework for this kind of analysis and it will probably be expended.
> Just my 2cents
> Regards,
> --
> Cédric
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