https://llvm.org/bugs/show_bug.cgi?id=30837
Bug ID: 30837
Summary: logf function call not auto-vectorizing
Product: libraries
Version: 3.9
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Loop Optimizer
Assignee: unassignedb...@nondot.org
Reporter: e...@ericmart.in
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Created attachment 17513
--> https://llvm.org/bugs/attachment.cgi?id=17513&action=edit
C test case, sh command to invoke clang, and example faulty IR
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.
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