[llvm-dev] Question about : lprofValueProfNodes

[Moshtaghi, Alireza via llvm-dev]

Thank you
So it does not seem to be relevant for what I’m trying to do.
I’m doing something unconventional.
The objective is to implement PGO and code coverage on a system that does not exit and does not have any file io, or any of  stdc libraries that libclang-profile is using. (more like a kernel)
So what I’m trying to do is instead of calling __llvm_profile_write_file () from the application, read the sections __llvm_prf_data, __llvm_prf_names, __llvm_prf_cnts and __llvm_prf_vnds after the critical tasks are done and transfer them to outside of the system.
Then dump these sections in a char * array in a c file and attribute them to be in the associated section.  Then compile that file with –u__llvm_profile_runtime to create an executable that calls __llvm_profile_write_file to dump my profraw data.

Sofar, I’m able to do the mechanics but seems like something is going wrong because because fprofile-instr-use does not find profile data for the source files.

Any suggestion?

Thanks
A

From: <vsk at apple.com> on behalf of Vedant Kumar <vsk at apple.com>
Date: Tuesday, December 19, 2017 at 11:32 AM
To: "Moshtaghi, Alireza" <Alireza.Moshtaghi at netapp.com>
Cc: llvm-dev <llvm-dev at lists.llvm.org>, Xinliang David Li <davidxl at google.com>
Subject: Re: [llvm-dev] Question about : lprofValueProfNodes

Hi,


On Dec 19, 2017, at 10:26 AM, Moshtaghi, Alireza via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:

Hi
This array is defined in compiler-rt: InstrProfilingValue.c but I can’t find where it is used?

It's used in allocateOneNode(). Incrementing the current vnode pointer gives a fresh node (possibly backed by the shared pool).



And the comment on it does not say much about why we need it either.

It's used to avoid calling malloc(), which David (CC'd) found to be a performance improvement.

best,
vedant


Can someone explain why we need this and where it is used?

/* A shared static pool in addition to the vnodes statically
* allocated by the compiler.  */
COMPILER_RT_VISIBILITY ValueProfNode
    lprofValueProfNodes[INSTR_PROF_VNODE_POOL_SIZE] COMPILER_RT_SECTION(COMPILER_RT_SEG INSTR_PROF_VNODES_SECT_NAME_STR);

Thanks
A

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