On Mon, Nov 26, 2018 at 12:45:26AM +0100, Carl Eugen Hoyos wrote: > 2018-11-25 16:17 GMT+01:00, Lauri Kasanen <c...@gmx.com>: > > Hi, > > > > The lone power8 fate failing test seems like an aliasing issue. > > I've isolated it into the attached standalone test case. Compiling it > > with > > gcc -std=c11 -maltivec -mabi=altivec -mvsx -O3 -fno-tree-vectorize > > -o test test.c > > > > reproduces on gcc 8.2.0, dropping the optimization level fixes it. This > > was one of the "adding a printf made it work" things too. > > > > -Wstrict-aliasing=1 complains about the "register int *idataptr = > > (int*)dataptr;" cast. If I put "typedef int __attribute__((may_alias)) > > int_alias;" at the top and change the cast and type to int_alias, the > > results become correct. > > Thank you for the analysis! > > Patch attached, Carl Eugen
> jrevdct.c | 17 +++++++++-------- > 1 file changed, 9 insertions(+), 8 deletions(-) > fef3d295836588ff8e619d4aa42247b4d2f25e93 > 0001-lavc-jrevdct-Avoid-an-aliasing-violation.patch > From e5403b832f2bcd360128d9986b602484e576c931 Mon Sep 17 00:00:00 2001 > From: Carl Eugen Hoyos <ceffm...@gmail.com> > Date: Mon, 26 Nov 2018 00:43:46 +0100 > Subject: [PATCH] lavc/jrevdct: Avoid an aliasing violation. > > Fixes fate on different PowerPC systems with some compilers. > > Analyzed-by: Lauri Kasanen > --- > libavcodec/jrevdct.c | 17 +++++++++-------- > 1 file changed, 9 insertions(+), 8 deletions(-) > > diff --git a/libavcodec/jrevdct.c b/libavcodec/jrevdct.c > index 3b15a52..c749468 100644 > --- a/libavcodec/jrevdct.c > +++ b/libavcodec/jrevdct.c > @@ -63,6 +63,7 @@ > */ > > #include "libavutil/common.h" > +#include "libavutil/intreadwrite.h" > > #include "dct.h" > #include "idctdsp.h" > @@ -234,7 +235,7 @@ void ff_j_rev_dct(DCTBLOCK data) > * row DCT calculations can be simplified this way. > */ > > - register int *idataptr = (int*)dataptr; > + register uint8_t *idataptr = (uint8_t*)dataptr; > > /* WARNING: we do the same permutation as MMX idct to simplify the > video core */ > @@ -254,10 +255,10 @@ void ff_j_rev_dct(DCTBLOCK data) > int16_t dcval = (int16_t) (d0 * (1 << PASS1_BITS)); > register int v = (dcval & 0xffff) | ((dcval * (1 << 16)) & > 0xffff0000); > > - idataptr[0] = v; > - idataptr[1] = v; > - idataptr[2] = v; > - idataptr[3] = v; > + AV_WN32(&idataptr[ 0], v); > + AV_WN32(&idataptr[ 4], v); > + AV_WN32(&idataptr[ 8], v); > + AV_WN32(&idataptr[12], v); this probably should be AV_WN32A() [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Those who are best at talking, realize last or never when they are wrong.
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