First, allow the case for negative powers of two. Then ensure that we
use the absolute value of the non-constant value to calculate the
quotient -- this was hinted in the code by the name 'uq'.
This fixes an issue when 'd' is positive and 'n' is negative. The
ishr will propagate the negative sign and we'll use nir_ineg() again,
incorrectly.
v2: First version used only ishr, but that isn't sufficient, since it
never can produce a zero as a result. (Jason)
Allow negative powers of two. (Caio)
Fixes: 74492ebad9 "nir: Add a pass for lowering integer division by constants"
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
v2: remove & operator in a couple of memsets
add some memsets
v3: fixup lima
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net> (v2)
It's a reasonably well-known fact in the world of compilers that integer
divisions by constants can be replaced by a multiply, an add, and some
shifts. This commit adds such an optimization to NIR for easiest case
of udiv. Other division operations will be added in following commits.
In order to provide some additional driver control, the pass takes a
minimum bit size to optimize.
Reviewed-by: Ian Romanick ian.d.romanick@intel.com
