https://bugs.llvm.org/show_bug.cgi?id=33921
Bug ID: 33921
Summary: ARM NEON vectorization miscompiles code in 5.0
Product: libraries
Version: 5.0
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: ARM
Assignee: unassignedb...@nondot.org
Reporter: mar...@martin.st
CC: llvm-bugs@lists.llvm.org
Starting with SVN r306803, some C code that wasn't vectorized before now is
vectorized. This seems to break e.g. some VP9 inverse transforms in libavcodec,
in code like this:
https://git.libav.org/?p=libav.git;a=blob;f=libavcodec/vp9dsp.c;h=7f863943284b8970744c81b0b7d749e5c9cf8bdf;hb=2b1324bd167553f49736e4eaa94f96da9982925e#l947
with the idct8_1d and iadst8_1d functions. If this file is built with
-fno-tree-vectorize, the issue disappears.
This regressed when upgrading from SVN r305659 to the 5.0 branch point:
https://fate.libav.org/armv7-win32-clang-5.0
Bisecting this leads to SVN r306803. The same issue can also be reproduced when
targeting linux, not only windows. It should be reproducable by building libav
and running "make fate-checkasm-vp9dsp", which should pass unless this is
miscompiled.
I will dig into it further, hopefully soon, to fill in with a better
reproducable testcase of the issue.
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