On 22/08/17 12:28, Marek Olšák wrote:
On Tue, Aug 22, 2017 at 1:10 PM, Jose Fonseca <jfons...@vmware.com> wrote:
On 20/08/17 01:49, Marek Olšák wrote:
From: Marek Olšák <marek.ol...@amd.com>
use COS+SIN instead.
I don't know if any existing gallium driver leverages that, but it's a basic
trigonometric principle that one can easily extract the sin from cos or
vice-versa. It requires some extra care for getting the right sign. But
the fact is that it should be considerably cheaper to comput both
simultaneously than indepdently.
Unfortunately GLSL/SPIR-V doesn't allow to express that. D3D9/D3D11 and
Metal all do. And from what I've seen from D3D9/D3D11 apps, 99% of the
times the shader wants both SIN/COS at the same time.
If we want one opcode to rule them all, then a combined SIN+COS seems a
better choice IMO. On SM4 the sincos has two outputs:
https://msdn.microsoft.com/en-us/library/windows/desktop/hh447234.aspx but
they are both optional to use. I don't know if there's a precedent for
that. I recall we had similar discussions about UMUL/UMUL_HI, and I suspect
we chose not to go that route.
Don't GPUs allow to express the computation of both sin/cos with a single
opcode? If nothing else there would be a non-negligible impact of
leveraging this in llvmpipe at some point. On the other hand, is possible
that LLVM common-subexpression elimination optimization passes already do
that, so we gain nothing.
In short, not big deal either way, but I think it's worth give it a 2nd
thought here.
R300 doesn't have trigonometric functions. R500, R600 and later VLIW
chips, and GCN all only have separate sin and cos.
svga is the only driver that has sincos. No gallium hardware driver has that.
I see. Fair enough. Considering that, plus the fact that GLSL doesn't
have conbined sin/cos, and that LLVM will most likely eliminate common
expressions generated by llvmpipe for cos/sin with same arg, there's
really not a significant upside left to justify keeping this around.
FWIW the patch is
Acked-by: Jose Fonseca <jfons...@vmware.com>
Jose
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