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I tracked down the bug to an incorrect use of restrict. I would not consider this a compiler bug: we are lying to the optimizer by telling it that a pointer is restrict when in fact it isn't. This can be fixed like so: diff --git a/celt/mdct.c b/celt/mdct.c index 1634e8e..fa5098c 100644 --- a/celt/mdct.c +++ b/celt/mdct.c @@ -276,8 +276,8 @@ void clt_mdct_backward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scala /* Post-rotate and de-shuffle from both ends of the buffer at once to make it in-place. */ { - kiss_fft_scalar * OPUS_RESTRICT...

After a few experiments, I found that both alternatives are very similar, and 2~5% slower compared to the following: diff --git a/celt/mdct.c b/celt/mdct.c index 1634e8e..e490c3b 100644 --- a/celt/mdct.c +++ b/celt/mdct.c @@ -277,7 +277,7 @@ void clt_mdct_backward(const mdct_lookup *l, kiss_fft_scalar *in, kiss_fft_scala it in-place. */ { kiss_fft_scalar * OPUS_RESTRICT yp0 = out+(overlap>>1); - kiss_fft_scalar * OPUS_RESTRICT yp1 = out...

...n the bug to an incorrect use of restrict. > > I would not consider this a compiler bug: we are lying to the optimizer by > telling it that a pointer is restrict when in fact it isn't. > > This can be fixed like so: > > > diff --git a/celt/mdct.c b/celt/mdct.c > index 1634e8e..fa5098c 100644 > --- a/celt/mdct.c > +++ b/celt/mdct.c > @@ -276,8 +276,8 @@ void clt_mdct_backward(const mdct_lookup *l, > kiss_fft_scalar *in, kiss_fft_scala > /* Post-rotate and de-shuffle from both ends of the buffer at once to > make > it in-place. */ >...

Hi, Apologies if this is a known issue, but running make on revision e3187444692195957eb66989622c7b1ad8448b06 fails one of the tests when using fixed point configuration (floating point is ok) on my linux x86. Note that libopus1.1, as extracted from the tar ball, is OK. Specifically, the tests that fail are in celt/tests/test_unit_mdct: nfft=32 inverse=0,snr = 85.341197 nfft=32 inverse=1,snr =