(In reply to Marek Ol=C5=A1=C3=A1k from comment #11)
> Thanks Grigori.
>=20
> GLSL:
>   color =3D fract(gl_FragCoord.y / 2) < 0.5 ?
>              texture(texture0, texcoord0) :
>              texture(texture1, texcoord0);
>=20
> texture0 and texture1 are SMEM loads.
>=20
> LLVM (SimplifyCFG) transforms it to:
>   color =3D texture(fract(gl_FragCoord.y / 2) < 0.5 ? texture0 : te=
xture1,
>                   texcoord0);
>=20
> That's a nice transformation. You don't have to use 2 SMEM loads, you =
can
> just use one SMEM load depending on the result of the condition.
>=20
> The problem is gl_FragCoord.y is a VGPR and texture0/1 are SGPRs, ther=
efore
> flat VMEM loads are used to load the descriptors. However, image_sample
> requires descriptors in SGPRs, so v_readfirstlane is used. That effect=
ively
> uses the result of the condition from the first active lane, discardin=
g the
> results from all other lanes. The result would be exactly the same if =
the
> compiler did: v_readfirstlane s0, gl_FragCoord.y;
>=20
> The test case seems pretty trivial I wonder how many other apps are af=
fected.

I think the best solution here would be to teach the backend how to do a sc=
alar
select based on value of vccz.