nv50/ir: fake SV_THREAD_KILL support

If we say that there are no helper invocations, it's suboptimal but
allows ES 3.1 to chug along.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10162>

src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nv50.cpp

@@ -1230,6 +1230,11 @@ NV50LoweringPreSSA::handleRDSV(Instruction *i)
                  off);
       break;
    }
+   case SV_THREAD_KILL:
+      // Not actually supported. But it's implementation-dependent, so we can
+      // always just say it's not a helper.
+      bld.mkMov(def, bld.loadImm(NULL, 0));
+      break;
    default:
       bld.mkFetch(i->getDef(0), i->dType,
                   FILE_SHADER_INPUT, addr, i->getIndirect(0, 0), NULL);

src/gallium/drivers/nouveau/codegen/nv50_ir_target_nv50.cpp

@@ -261,6 +261,8 @@ TargetNV50::getSVAddress(DataFile shaderFile, const Symbol *sym) const
       return 0;
    case SV_SAMPLE_POS:
       return 0; /* sample position is handled differently */
+   case SV_THREAD_KILL:
+      return 0;
    default:
       return sysvalLocation[sym->reg.data.sv.sv];
    }