Extended Description

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.