diff --git a/src/compiler/nir/nir_builder.h b/src/compiler/nir/nir_builder.h
index 6bf4be84aa8..72779cde4dd 100644
--- a/src/compiler/nir/nir_builder.h
+++ b/src/compiler/nir/nir_builder.h
@@ -1580,6 +1580,29 @@ nir_resize_vector(nir_builder *b, nir_def *src, unsigned num_components)
       return nir_trim_vector(b, src, num_components);
 }
 
+/* Shift channels to the left or right. Fill undefined components with .x.
+ * Examples:
+ *    channel_shift =  1, new_num_components = 4: .xyzw -> .xxyz
+ *    channel_shift = -1, new_num_components = 3: .xyzw -> .yzw
+ */
+static inline nir_def *
+nir_shift_channels(nir_builder *b, nir_def *def, int channel_shift,
+                   unsigned new_num_components)
+{
+   if (channel_shift == 0)
+      return nir_resize_vector(b, def, new_num_components);
+
+   assert(abs(channel_shift) < NIR_MAX_VEC_COMPONENTS);
+   unsigned swizzle[NIR_MAX_VEC_COMPONENTS] = {0};
+
+   for (int i = 1; i < def->num_components; i++) {
+      if (i + channel_shift >= 0)
+         swizzle[i + channel_shift] = i;
+   }
+
+   return nir_swizzle(b, def, swizzle, new_num_components);
+}
+
 nir_def *
 nir_ssa_for_alu_src(nir_builder *build, nir_alu_instr *instr, unsigned srcn);
 
diff --git a/src/mesa/state_tracker/st_nir_unlower_io_to_vars.c b/src/mesa/state_tracker/st_nir_unlower_io_to_vars.c
index 81292a72770..853fe1153d0 100644
--- a/src/mesa/state_tracker/st_nir_unlower_io_to_vars.c
+++ b/src/mesa/state_tracker/st_nir_unlower_io_to_vars.c
@@ -614,28 +614,8 @@ unlower_io_to_vars(nir_builder *b, nir_intrinsic_instr *intr, void *opaque)
 
    if (desc.is_store) {
       unsigned writemask = nir_intrinsic_write_mask(intr) << desc.component;
-      nir_def *value = intr->src[0].ssa;
-
-      if (desc.component) {
-         unsigned new_num_components = desc.component + value->num_components;
-         unsigned swizzle[4] = {0};
-         assert(new_num_components <= 4);
-
-         /* Move components within the vector to the right because we only
-          * have vec4 stores. The writemask skips the extra components at
-          * the beginning.
-          *
-          * For component = 1: .xyz -> .xxyz
-          * For component = 2: .xy  -> .xxxy
-          * For component = 3: .x   -> .xxxx
-          */
-         for (unsigned i = 1; i < value->num_components; i++)
-            swizzle[desc.component + i] = i;
-
-         value = nir_swizzle(b, value, swizzle, new_num_components);
-      }
-
-      value = nir_resize_vector(b, value, num_components);
+      nir_def *value = nir_shift_channels(b, intr->src[0].ssa, desc.component,
+                                          num_components);
 
       /* virgl requires scalarized TESS_LEVEL stores because originally
        * the GLSL compiler never vectorized them. Doing 1 store per bit of