[PATCH] R600/SI: Use source modifiers for f64 fabs / fneg

[Michel Dänzer]

On 02.08.2014 11:33, Matt Arsenault wrote:
> f32 has a comment and patterns about the behavior with 0 and negate
> modifier which I'm unsure about. I think the source modifier should
> work if the source is 0, since the negate modifier is supposed to be
> applied before abs. Does this pattern need to be skipped for f64
> too?

The original problem was that fneg was implemented as V_ADD_F32_e64 of 0
and the operand with the negate source modifier set. This resulted in
+0.0 instead of -0.0 (i.e. the sign bit was not set) for an argument of
+0.0. There's a (graphics) piglit test which failed because of that.

Given that FNEG_SI and FABS_SI directly manipulate the sign bit, I
wouldn't expect that to require any special treatment anymore. As you
say, the source modifiers should work fine when folding these into other
operations.

So, I suspect the purpose of the (fneg (fabs)) pattern isn't to avoid
that problem but to avoid expanding both FABS_SI and FABS_SI.


-- 
Earthling Michel Dänzer            |                  http://www.amd.com
Libre software enthusiast          |                Mesa and X developer