llvm dev - May 2016 - Access to dynamic execution information.

Hi
Does LLVM dynamically run the program to obtain profiling information like
branch weight? if so, can we access the information regarding this run like
the number of instructions that have been executed dynamically between two
specific points of the program?

Thanks
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Hi,

depending on your specific use case you could have a look at the Sulong
project (https://github.com/graalvm/sulong/). Sulong can execute LLVM IR
programs and gathers profiling information during the program's execution.
For example, Sulong profiles the frequency of successor blocks in the
interpreter, to then communicate it to the dynamic compiler for better
optimization [1]. Similarly, you could implement a node that counts the
number of executed instructions between two points in the program and
instantiate it in the parser [2].

- Manuel

[1]
https://github.com/graalvm/sulong/blob/master/projects/com.oracle.truffle.llvm.nodes.impl/src/com/oracle/truffle/llvm/nodes/impl/base/LLVMBasicBlockNode.java
[2]
https://github.com/graalvm/sulong/blob/master/projects/com.oracle.truffle.llvm.parser.impl/src/com/oracle/truffle/llvm/parser/impl/LLVMVisitor.java

2016-05-13 16:35 GMT+02:00 fateme Hoseini via llvm-dev <
llvm-dev at lists.llvm.org>:
> Hi
> Does LLVM dynamically run the program to obtain profiling information like
> branch weight? if so, can we access the information regarding this run like
> the number of instructions that have been executed dynamically between two
> specific points of the program?
>
> Thanks
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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On Fri, May 13, 2016 at 8:35 AM fateme Hoseini via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi
> Does LLVM dynamically run the program to obtain profiling information like
> branch weight?
>
No, the profile information is either collected via instrumentation of the
program or via external sampling profilers. It is then read back into the
IR by the frontend or an optimization pass.

> if so, can we access the information regarding this run like the number of
> instructions that have been executed dynamically between two specific
> points of the program?
>
If Manuel Rigger's suggestion doesn't work, maybe try Valgrind which can
get these kinds of instruction counts?
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Thank you for your reply.

No, the profile information is either collected via instrumentation of
the
> program or via external sampling profilers. It is then read back into the
> IR by the frontend or an optimization pass.
>
Does LLVM use instruction instrumention?

I am particularly looking for a program that create this profiling
information dynamically, i.e., from the machine code. And preferably has
the fault injection, detection ability.
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