diff --git a/src/amd/common/nir/ac_nir.c b/src/amd/common/nir/ac_nir.c
index ffdbbe4b472..3860df8848a 100644
--- a/src/amd/common/nir/ac_nir.c
+++ b/src/amd/common/nir/ac_nir.c
@@ -1049,3 +1049,131 @@ ac_nir_opt_vectorize_cb(const nir_instr *instr, const void *data)
 
    return target_width;
 }
+
+/* The IO driver location is computed from shader_info masks using a prefix bitcount.
+ * Used by FS inputs, and radeonsi+LLVM also uses this for LS outputs to VGPRs and FS outputs.
+ *
+ * driver_location == nir_intrinsic_base == nir_variable::data::driver_location.
+ */
+unsigned
+ac_nir_get_io_driver_location(const nir_shader *nir, unsigned location, bool is_input)
+{
+   assert((nir->info.stage == MESA_SHADER_VERTEX && !is_input) ||
+          nir->info.stage == MESA_SHADER_FRAGMENT);
+   /* All "read" bits should also be set in "written" bits. */
+   assert(!(nir->info.outputs_read & ~nir->info.outputs_written));
+   assert(!(nir->info.outputs_read_16bit & nir->info.outputs_written_16bit));
+
+   /* Per-vertex masks. */
+   uint64_t mask = is_input ? nir->info.inputs_read : nir->info.outputs_written;
+   uint16_t mask16 = is_input ? nir->info.inputs_read_16bit : nir->info.outputs_written_16bit;
+   uint64_t back_color_mask = 0;
+
+   /* Handle FS outputs first. */
+   if (nir->info.stage == MESA_SHADER_FRAGMENT && !is_input) {
+      assert(mask & BITFIELD64_BIT(location));
+      return util_bitcount64(mask & BITFIELD64_MASK(location));
+   }
+
+   /* Per-primitive masks. */
+   uint64_t mask_maybe_per_prim = 0;
+   uint64_t mask_per_prim = 0;
+   uint16_t mask16_per_prim = 0;
+   bool maybe_per_primitive = false;
+   bool per_primitive = false;
+
+   /* Fragment shader input locations must be in this order: per-vertex, maybe per-prim, per-prim. */
+   if (nir->info.stage == MESA_SHADER_FRAGMENT && is_input) {
+      if (BITSET_TEST(nir->info.system_values_read, SYSTEM_VALUE_COLOR0_AMD))
+         mask |= VARYING_BIT_COL0;
+      if (BITSET_TEST(nir->info.system_values_read, SYSTEM_VALUE_COLOR1_AMD))
+         mask |= VARYING_BIT_COL1;
+
+      /* TODO: back colors are broken with mesh shaders because they are always after per-primitive
+       * inputs.
+       */
+      back_color_mask = mask & (VARYING_BIT_BFC0 | VARYING_BIT_BFC1);
+
+      assert(!(mask & VARYING_BIT_LAYER)); /* This should have been lowered. */
+      mask_maybe_per_prim = mask & (VARYING_BIT_PRIMITIVE_ID | VARYING_BIT_VIEWPORT);
+      mask_per_prim = mask & nir->info.per_primitive_inputs &
+                      ~(VARYING_BIT_PRIMITIVE_ID | VARYING_BIT_VIEWPORT);
+
+      /* TODO: Add shader_info::per_primitive_inputs_16bit for separate GLES mesh shaders + mediump. */
+      /*mask16_per_prim = mask & nir->info.per_primitive_inputs_16bit;*/
+
+      /* Make the masks disjoint. */
+      mask &= ~(back_color_mask | mask_maybe_per_prim | mask_per_prim);
+      mask16 &= ~mask16_per_prim;
+
+      if (location == VARYING_SLOT_PRIMITIVE_ID || location == VARYING_SLOT_VIEWPORT) {
+         maybe_per_primitive = true;
+      } else if (location >= VARYING_SLOT_VAR0_16BIT) {
+         /* TODO: Add shader_info::per_primitive_inputs_16bit. */
+         /*per_primitive = nir->info.per_primitive_inputs_16bit &
+                         BITFIELD_BIT(location - VARYING_SLOT_VAR0_16BIT);*/
+      } else {
+         assert(location <= VARYING_SLOT_VAR31);
+         per_primitive = nir->info.per_primitive_inputs & BITFIELD64_BIT(location);
+      }
+   }
+
+   enum {
+      MASK,
+      MASK16,
+      MASK_MAYBE_PRIM_PRIM, /* always after per-vertex varyings (NUM_INTERP) */
+      MASK_PER_PRIM,
+      MASK16_PER_PRIM,
+      BACK_COLOR_MASK, /* always after all other varyings */
+      PARAM_GEN_MASK, /* PARAM_GEN is loaded at location (NUM_INTERP + NUM_PRIM_INTERP). */
+   };
+
+   /* We'll compute a prefix bitcount from this bitset. */
+   const uint64_t masks[] = {
+      [MASK] = mask,
+      [MASK16] = mask16,
+      [MASK_MAYBE_PRIM_PRIM] = mask_maybe_per_prim,
+      [MASK_PER_PRIM] = mask_per_prim,
+      [MASK16_PER_PRIM] = mask16_per_prim,
+      [BACK_COLOR_MASK] = back_color_mask,
+      [PARAM_GEN_MASK] = 0,
+   };
+   unsigned location_mask_index;
+
+   /* Assign a mask index to the location, and make "location" relative to the beginning of its mask. */
+   if (nir->info.stage == MESA_SHADER_FRAGMENT && is_input && location == VARYING_SLOT_PARAM_GEN_AMD)
+      location_mask_index = PARAM_GEN_MASK;
+   else if (nir->info.stage == MESA_SHADER_FRAGMENT && is_input &&
+            (location == VARYING_SLOT_BFC0 || location == VARYING_SLOT_BFC1))
+      location_mask_index = BACK_COLOR_MASK;
+   else if (per_primitive)
+      location_mask_index = location >= VARYING_SLOT_VAR0_16BIT ? MASK16_PER_PRIM : MASK_PER_PRIM;
+   else if (maybe_per_primitive)
+      location_mask_index = MASK_MAYBE_PRIM_PRIM;
+   else
+      location_mask_index = location >= VARYING_SLOT_VAR0_16BIT ? MASK16 : MASK;
+
+   /* Make "location" relative to its mask. */
+   if (location >= VARYING_SLOT_VAR0_16BIT)
+      location -= VARYING_SLOT_VAR0_16BIT;
+
+   /* Compute the prefix bitcount. */
+   unsigned index = 0;
+
+   for (unsigned i = 0; i < location_mask_index; i++)
+      index += util_bitcount64(masks[i]);
+
+   index += util_bitcount64(masks[location_mask_index] & BITFIELD64_MASK(location));
+
+#if 0 /* useful debug code */
+   printf("location_mask_index=%u\n", location_mask_index);
+   for (unsigned i = 0; i <= location_mask_index; i++)
+      printf("mask[%u] = 0x%lx\n", i, masks[i]);
+
+   printf("index=%u, location=%u, %s, num=%u\n",
+          index, location, is_input ? "input" : "output",
+          is_input ? nir->num_inputs : nir->num_outputs);
+#endif
+
+   return index;
+}
diff --git a/src/amd/common/nir/ac_nir.h b/src/amd/common/nir/ac_nir.h
index 8578747d853..eb785c3c84a 100644
--- a/src/amd/common/nir/ac_nir.h
+++ b/src/amd/common/nir/ac_nir.h
@@ -469,6 +469,9 @@ ac_nir_op_supports_packed_math_16bit(const nir_alu_instr* alu);
 uint8_t
 ac_nir_opt_vectorize_cb(const nir_instr *instr, const void *data);
 
+unsigned
+ac_nir_get_io_driver_location(const nir_shader *nir, unsigned location, bool is_input);
+
 #ifdef __cplusplus
 }
 #endif