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avcodec/svq1enc: Workaround GCC bug 102513

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GCC 11 has a bug: When it creates clones of recursive functions
(to inline some parameters), it clones a recursive function
eight times by default, even when this exceeds the recursion
depth. This happens with encode_block() in libavcodec/svq1enc.c
where a parameter level is always in the range 0..5;
but GCC 11 also creates functions corresponding to level UINT_MAX
and UINT_MAX - 1 (on -O3; -O2 is fine).

Using such levels would produce undefined behaviour and because
of this GCC emits bogus -Warray-bounds warnings for these clones.

Since commit d08b2900a9, certain
symbols that are accessed like ff_svq1_inter_multistage_vlc[level]
are declared with hidden visibility, which allows compilers
to bake the offset implied by level into the instructions
if level is a compile-time constant as it is in the clones.
Yet this leads to insane offsets for level == UINT_MAX which
can be incompatible with the supported offset ranges of relocations.
This happens in the small code model (the default code model for
AArch64).

This commit therefore works around this bug by disabling cloning
recursive functions for GCC 10 and 11. GCC 10 is affected by the
underlying bug (see
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102513), so the workaround
also targets it, although it only produces three versions of
encode_block(), so it does not seem to trigger the actual issue here.

The issue has been mitigated in GCC 12.1 (it no longer creates clones
for impossible values; see also commit
1cb7fd317c), so the workaround
does not target it.

Reported-by: J. Dekker <jdek@itanimul.li>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Signed-off-by: J. Dekker <jdek@itanimul.li>
This commit is contained in:
Andreas Rheinhardt 2022-10-25 14:48:48 +02:00 committed by J. Dekker
parent 7aa5ea237f
commit 894191e7e1
1 changed files with 6 additions and 0 deletions
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6
libavcodec/svq1enc.c
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@ -46,6 +46,12 @@
#include "libavutil/frame.h"
#include "libavutil/mem_internal.h"
// Workaround for GCC bug 102513
#if AV_GCC_VERSION_AT_LEAST(10, 0) && AV_GCC_VERSION_AT_MOST(12, 0) \
&& !defined(__clang__) && !defined(__INTEL_COMPILER)
#pragma GCC optimize ("no-ipa-cp-clone")
#endif
typedef struct SVQ1EncContext {
/* FIXME: Needed for motion estimation, should not be used for anything
* else, the idea is to make the motion estimation eventually independent