nv50/ir: optimize SHLADD(a, b, c) to MOV((a << b) + c)

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>

src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp

@@ -778,6 +778,9 @@ ConstantFolding::expr(Instruction *i,
       }
       break;
    }
+   case OP_SHLADD:
+      res.data.u32 = (a->data.u32 << b->data.u32) + c->data.u32;
+      break;
    default:
       return;
    }