llvm dev - Oct 2016 - Bug with auto-vectorization of logf

Hi,
I intended to file this bug on Bugzilla, but I've received no response from
llvm-admin in the 10 days since asking for a Bugzilla account.

I've written 2 test functions in C that take in a float array x of size n
and output float array f(x), where f is either fabsf or logf. The LLVM 3.9
auto-vectorization docs claim that both functions will be vectorized:
http://llvm.org/releases/3.9.0/docs/Vectorizers.html#vectorization-of-function-calls

When running with "clang -O3 -march=x86-64 -mavx2 -ffast-math test.c -S
-emit-llvm", the function calling fabsf is vectorized while the function
calling logf is not.  This is with clang 3.9, but I've also confirmed the
bug exists back to at least clang 3.7. I've also observed that logf calls
break vectorization of more complex loops, and I provide the comparison
with fabsf as a reduced test case.

I've attached the C program, a sh script to invoke clang with correct
arguments, and an example LLVM IR file I produced by running on my system.

If someone makes a Bugzilla account for me, I can refile this bug there.

Best,
Eric Martin
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+Tanya for the account issue.
> On Oct 27, 2016, at 11:36 AM, Eric Martin via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi,
> I intended to file this bug on Bugzilla, but I've received no response
from llvm-admin in the 10 days since asking for a Bugzilla account.
> 
> I've written 2 test functions in C that take in a float array x of size
n and output float array f(x), where f is either fabsf or logf. The LLVM 3.9
auto-vectorization docs claim that both functions will be vectorized:
http://llvm.org/releases/3.9.0/docs/Vectorizers.html#vectorization-of-function-calls
<http://llvm.org/releases/3.9.0/docs/Vectorizers.html#vectorization-of-function-calls>
> 
> When running with "clang -O3 -march=x86-64 -mavx2 -ffast-math test.c
-S -emit-llvm", the function calling fabsf is vectorized while the function
calling logf is not.  This is with clang 3.9, but I've also confirmed the
bug exists back to at least clang 3.7. I've also observed that logf calls
break vectorization of more complex loops, and I provide the comparison with
fabsf as a reduced test case.
> 
> I've attached the C program, a sh script to invoke clang with correct
arguments, and an example LLVM IR file I produced by running on my system.
> 
> If someone makes a Bugzilla account for me, I can refile this bug there.
> 
> Best,
> Eric Martin
> 
> <log_autovec_test.tgz>_______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Eric,

I apologize for any delay or confusion. From my records/list archives, I saw
that Anton had created an account for you on Oct 17th and responded to your
email to llvm-admin. I am not sure what happened after that point as I thought
the account was done.

I just confirmed there is an account for you in bugzilla, so you should be good
to go if you reset your password.

-Tanya
> On Oct 27, 2016, at 11:47 AM, Mehdi Amini <mehdi.amini at apple.com>
wrote:
> 
> +Tanya for the account issue.
> 
>> On Oct 27, 2016, at 11:36 AM, Eric Martin via llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> 
>> Hi,
>> I intended to file this bug on Bugzilla, but I've received no
response from llvm-admin in the 10 days since asking for a Bugzilla account.
>> 
>> I've written 2 test functions in C that take in a float array x of
size n and output float array f(x), where f is either fabsf or logf. The LLVM
3.9 auto-vectorization docs claim that both functions will be vectorized:
http://llvm.org/releases/3.9.0/docs/Vectorizers.html#vectorization-of-function-calls
<http://llvm.org/releases/3.9.0/docs/Vectorizers.html#vectorization-of-function-calls>
>> 
>> When running with "clang -O3 -march=x86-64 -mavx2 -ffast-math
test.c -S -emit-llvm", the function calling fabsf is vectorized while the
function calling logf is not.  This is with clang 3.9, but I've also
confirmed the bug exists back to at least clang 3.7. I've also observed that
logf calls break vectorization of more complex loops, and I provide the
comparison with fabsf as a reduced test case.
>> 
>> I've attached the C program, a sh script to invoke clang with
correct arguments, and an example LLVM IR file I produced by running on my
system.
>> 
>> If someone makes a Bugzilla account for me, I can refile this bug
there.
>> 
>> Best,
>> Eric Martin
>> 
>>
<log_autovec_test.tgz>_______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
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