Observed in a shader from Resident Evil Village.
This also helps prevent emitting invalid IR.
Cc: mesa-stable
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12599>
case nir_op_fddy_fine:
case nir_op_fddx_coarse:
case nir_op_fddy_coarse: {
+ if (!nir_src_is_divergent(instr->src[0].src)) {
+ /* Source is the same in all lanes, so the derivative is zero.
+ * This also avoids emitting invalid IR.
+ */
+ bld.copy(Definition(dst), Operand::zero());
+ break;
+ }
+
Temp src = as_vgpr(ctx, get_alu_src(ctx, instr->src[0]));
uint16_t dpp_ctrl1, dpp_ctrl2;
if (instr->op == nir_op_fddx_fine) {