[cfe-users] Fwd: floor is vectorized, but not sin, cos or exp

Jonas Toth via cfe-users cfe-users at lists.llvm.org
Tue Dec 11 08:28:38 PST 2018

I am forwarding this to cfe-dev as it might this sounds like a bug and
cfe-users is not read that much.

-------- Weitergeleitete Nachricht --------
Betreff: 	[cfe-users] floor is vectorized, but not sin, cos or exp
Datum: 	Tue, 11 Dec 2018 16:47:16 +0100
Von: 	Klaus Leppkes via cfe-users <cfe-users at lists.llvm.org>
Antwort an: 	Klaus Leppkes <klaus.leppkes at rwth-aachen.de>
An: 	cfe-users at lists.llvm.org


according to the doc
(https://releases.llvm.org/7.0.0/docs/Vectorizers.html) floor, sin, cos
should be vectorized.

I can confirm (using the great https://gcc.godbolt.org/ tool) that using
the flags "-Ofast -mavx2  -fopenmp -ffast-math" the right avx2 opcode
(vroundps) is emited for floor (in foo), but unfortunately not for sin,
cos or exp (e.g. see sin in bar below).

GCC 8.1+ and the Intel Compiler icc 13+ insert call to vectorized
implementations (_ZGVbN4v_sinf or __svml_sinf4 ), but clang seems to
have nothing like this.

Here is my small testcode:


voidfoo(float* __restrict__attribute((aligned(32))) x
, float* __restrict__attribute((aligned(32))) y) {
for(inti = 0; i < 4; ++i)
y[i] = floor(x[i]);

voidbar(float* __restrict__attribute((aligned(32))) x
, float* __restrict__attribute((aligned(32))) y) {
for(inti = 0; i < 4; ++i)
y[i] = sin(x[i]);

I have reproduced this behavior on different machines. Maybe I am doing
s.th. wrong here, but it seems like there is no vectorized
implementation for sin, cos etc. I am using h2lib for now
(http://h2lib.org/doc/d1/d89/simd__avx_8h_source.html) as a workaround,
but I expect clang to do this job.

Can anybody comment on this please?

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