Released Clang 12 generates bad code for the original loop in here.
While this is a compiler bug plain and simple, we still have to deal
with it.
This is related to the SLP vectorizer, and in particular the two
reverse subtracts in the butterflies for the second half to avoid
unary negates.
Use the more regular dataflow that has the unary negates in it
(we can at least fold one of them into a constant, namely for A2)
and introduce a few temporaries that also make alias analysis (and
possible block-level vectorization) a whole let easier while I'm at
it.
This fixes the codegen issues on Clang 12, which now produces a
working decoder, and I expect the single unary negate that we
actually gain per iteration of this loop is not a significant
perf concern. (There are bigger fish to fry here regardless.)
Fixes issue #1152.
Some parameters do not get used, or only when certain config
defines are set. Explicitly mark them as unused to make compilers
happy.
Fixes issue #396.
This is definitely unnecessary, or at least I can't find anything
in the Vorbis spec that would indicate anything special happening
here.
Fixes issue #816.
When start_decoder() fails it may already have allocated memory
for .vendor and/or .comment_list. Call vorbis_deinit() to free
any allocated memory.
Fixes issue #1051.
Not an actual bug, it just looked wonky, but this code runs
with code lengths that are verified to be in range (<32) by
the length-reading code. Anyway.
Fixes issue #901.
I propose to remove this line because f->valid_bits will never be less than zero since, in the while loop, you're adding 8 to it. Therefore, it will always evaluate to false. This is to help remove redundant code.
The eliminated code removes the (ch == 1) branch, which is scoped
within this if condition: `if (rtype == 2 && ch != 1)`, therefore
the (ch == 1) branch will never be taken.
Fixes#842.
In the call to decode_residue:
decode_residue(f, residue_buffers, ch, n2, r, do_not_decode);
The channel count is previously intialized as zero and incremented
based on a for-loop (f->channels) plus a conditional,
if (map->chan[j].mux == i). If this doesn't happen then 'ch'
remains zero.
Once inside decode_residue(..), the code has three branches based
on channel count: stereo (ch == 2), mono (ch == 1), and then the
exception if it's neither of those (simple 'else'). It's in here
where a zero-valued 'ch' can be used as the denominator in these
calculations:
int c_inter = z % ch
p_inter = z/ch;
Obviously this 'else' branch is meant for channel counts greater
than two an not for zero channels; so this change simply makes
that branch only valid if (ch > 2).
Sean Barrett
Fabian Giesen
morlad (iLeitgeb)
Johannes Schultz
AnthoFoxo
Rémi Verschelde
Pedro J. Estébanez
Clownacy
wph612
David Reid
Sean Barrett
Marco Lizza
Peter Waller
Kevin Croft
Dougall Johnson