[llvm-bugs] [Bug 33921] New: ARM NEON vectorization miscompiles code in 5.0
llvm-bugs at lists.llvm.org
Tue Jul 25 04:17:55 PDT 2017
Bug ID: 33921
Summary: ARM NEON vectorization miscompiles code in 5.0
Component: Backend: ARM
Assignee: unassignedbugs at nondot.org
Reporter: martin at martin.st
CC: llvm-bugs at 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:
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:
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
I will dig into it further, hopefully soon, to fill in with a better
reproducable testcase of the issue.
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