diff --git a/src/imagination/pco/meson.build b/src/imagination/pco/meson.build
index a912cca2666..7db2e010dc4 100644
--- a/src/imagination/pco/meson.build
+++ b/src/imagination/pco/meson.build
@@ -12,6 +12,7 @@ libpowervr_compiler_files = files(
   'pco_group_instrs.c',
   'pco_index.c',
   'pco_ir.c',
+  'pco_legalize.c',
   'pco_nir.c',
   'pco_nir_pvfio.c',
   'pco_opt.c',
diff --git a/src/imagination/pco/pco_internal.h b/src/imagination/pco/pco_internal.h
index c53b0b586c5..64a3d4b736a 100644
--- a/src/imagination/pco/pco_internal.h
+++ b/src/imagination/pco/pco_internal.h
@@ -337,6 +337,7 @@ typedef struct _pco_shader {
    const char *name; /** Shader name. */
    bool is_internal; /** Whether this is an internal shader. */
    bool is_grouped; /** Whether the shader uses igrps. */
+   bool is_legalized; /** Whether the shader has been legalized. */
 
    struct list_head funcs; /** List of functions. */
    unsigned next_func; /** Next function index. */
@@ -1112,6 +1113,7 @@ bool pco_dce(pco_shader *shader);
 bool pco_end(pco_shader *shader);
 bool pco_group_instrs(pco_shader *shader);
 bool pco_index(pco_shader *shader, bool skip_ssa);
+bool pco_legalize(pco_shader *shader);
 bool pco_nir_pfo(nir_shader *nir, pco_fs_data *fs);
 bool pco_nir_pvi(nir_shader *nir, pco_vs_data *vs);
 bool pco_opt(pco_shader *shader);
@@ -1946,6 +1948,47 @@ static inline bool pco_refs_are_equal(pco_ref ref0, pco_ref ref1)
    return true;
 }
 
+/**
+ * \brief Checks a reference has a valid hardware source mapping.
+ *
+ * \param[in] ref Reference.
+ * \param[in] mapped_src Hardware source mapping.
+ * \param[out] needs_s124 Whether the mapping needs to use S{1,2,4}
+ *                        rather than S{0,2,3}.
+ * \return True if the mapping is valid.
+ */
+static inline bool
+ref_src_map_valid(pco_ref ref, enum pco_io mapped_src, bool *needs_s124)
+{
+   if (needs_s124)
+      *needs_s124 = false;
+
+   /* Restrictions only apply to hardware registers. */
+   if (!pco_ref_is_idx_reg(ref) && !pco_ref_is_reg(ref))
+      return true;
+
+   switch (pco_ref_get_reg_class(ref)) {
+   case PCO_REG_CLASS_COEFF:
+   case PCO_REG_CLASS_SHARED:
+   case PCO_REG_CLASS_INDEX:
+   case PCO_REG_CLASS_PIXOUT:
+      return (mapped_src == PCO_IO_S0) || (mapped_src == PCO_IO_S2) ||
+             (mapped_src == PCO_IO_S3);
+
+   case PCO_REG_CLASS_SPEC:
+      if (needs_s124)
+         *needs_s124 = true;
+
+      return (mapped_src == PCO_IO_S1) || (mapped_src == PCO_IO_S2) ||
+             (mapped_src == PCO_IO_S4);
+
+   default:
+      return true;
+   }
+
+   return false;
+}
+
 /**
  * \brief Returns whether none of the lower/upper sources in an instruction
  *        group are set.
diff --git a/src/imagination/pco/pco_ir.c b/src/imagination/pco/pco_ir.c
index fbd05cafcd2..7b2dfe70795 100644
--- a/src/imagination/pco/pco_ir.c
+++ b/src/imagination/pco/pco_ir.c
@@ -60,6 +60,7 @@ void pco_process_ir(pco_ctx *ctx, pco_shader *shader)
     * time a drc result is used.
     */
    PCO_PASS(_, shader, pco_schedule);
+   PCO_PASS(_, shader, pco_legalize);
    PCO_PASS(_, shader, pco_ra);
    PCO_PASS(_, shader, pco_end);
    PCO_PASS(_, shader, pco_group_instrs);
diff --git a/src/imagination/pco/pco_legalize.c b/src/imagination/pco/pco_legalize.c
new file mode 100644
index 00000000000..2ef9f425388
--- /dev/null
+++ b/src/imagination/pco/pco_legalize.c
@@ -0,0 +1,136 @@
+/*
+ * Copyright © 2025 Imagination Technologies Ltd.
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+/**
+ * \file pco_legalize.c
+ *
+ * \brief PCO legalizing pass.
+ */
+
+#include "pco.h"
+#include "pco_builder.h"
+#include "pco_internal.h"
+#include "util/macros.h"
+
+#include <stdbool.h>
+
+/**
+ * \brief Insert a mov to legalize how a hardware register is referenced.
+ *
+ * \param[in,out] instr PCO instr.
+ * \param[in,out] ref Reference to be legalized.
+ * \param[in] needs_s124 Whether the mapping needs to use S{1,2,4}
+ *                       rather than S{0,2,3}.
+ * \return True if progress was made.
+ */
+static void insert_mov_ref(pco_instr *instr, pco_ref *ref, bool needs_s124)
+{
+   assert(pco_ref_is_scalar(*ref));
+   pco_ref new_ref = pco_ref_new_ssa(instr->parent_func,
+                                     pco_ref_get_bits(*ref),
+                                     pco_ref_get_chans(*ref));
+
+   pco_ref_xfer_mods(&new_ref, ref, true);
+
+   pco_builder b =
+      pco_builder_create(instr->parent_func, pco_cursor_before_instr(instr));
+
+   if (needs_s124)
+      pco_movs1(&b, new_ref, *ref);
+   else
+      pco_mbyp(&b, new_ref, *ref);
+
+   *ref = new_ref;
+}
+
+/**
+ * \brief Try to legalize an instruction's hardware source mappings.
+ *
+ * \param[in,out] instr PCO instr.
+ * \param[in] info PCO op info.
+ * \return True if progress was made.
+ */
+static bool try_legalize_src_mappings(pco_instr *instr,
+                                      const struct pco_op_info *info)
+{
+   bool progress = false;
+   bool needs_s124;
+
+   /* Check dests. */
+   pco_foreach_instr_dest (pdest, instr) {
+      unsigned dest_index = pdest - instr->dest;
+      if (!info->dest_intrn_map[dest_index])
+         continue;
+
+      enum pco_io mapped_src = PCO_IO_S0 + info->dest_intrn_map[dest_index] - 1;
+
+      if (ref_src_map_valid(*pdest, mapped_src, &needs_s124))
+         continue;
+
+      insert_mov_ref(instr, pdest, needs_s124);
+      progress = true;
+   }
+
+   /* Check srcs. */
+   pco_foreach_instr_src (psrc, instr) {
+      unsigned src_index = psrc - instr->src;
+      if (!info->src_intrn_map[src_index])
+         continue;
+
+      enum pco_io mapped_src = PCO_IO_S0 + info->src_intrn_map[src_index] - 1;
+
+      if (ref_src_map_valid(*psrc, mapped_src, &needs_s124))
+         continue;
+
+      insert_mov_ref(instr, psrc, needs_s124);
+      progress = true;
+   }
+
+   return progress;
+}
+
+/**
+ * \brief Try to legalizes an instruction.
+ *
+ * \param[in,out] instr PCO instr.
+ * \return True if progress was made.
+ */
+static bool try_legalize(pco_instr *instr)
+{
+   const struct pco_op_info *info = &pco_op_info[instr->op];
+   bool progress = false;
+
+   /* Skip pseudo instructions. */
+   if (info->type == PCO_OP_TYPE_PSEUDO)
+      return false;
+
+   progress |= try_legalize_src_mappings(instr, info);
+
+   return progress;
+}
+
+/**
+ * \brief Legalizes instructions where additional restrictions apply.
+ *
+ * \param[in,out] shader PCO shader.
+ * \return True if the pass made progress.
+ */
+bool pco_legalize(pco_shader *shader)
+{
+   bool progress = false;
+
+   assert(!shader->is_grouped);
+   assert(!shader->is_legalized);
+
+   pco_foreach_func_in_shader (func, shader) {
+      pco_foreach_instr_in_func_safe (instr, func) {
+         progress |= try_legalize(instr);
+      }
+   }
+
+   shader->is_legalized = true;
+   return progress;
+}
diff --git a/src/imagination/pco/pco_map.py b/src/imagination/pco/pco_map.py
index 01ed4452a8f..682f39452e7 100644
--- a/src/imagination/pco/pco_map.py
+++ b/src/imagination/pco/pco_map.py
@@ -781,6 +781,18 @@ encode_map(O_MOVC,
    ]
 )
 
+encode_map(O_MOVWM,
+   encodings=[
+      (I_MOVC_EXT, [
+         ('movw0', ('pco_ref_get_movw01', SRC(0))),
+         ('movw1', 0),
+         ('maskw0', (RM_ELEM, DEST(0))),
+         ('aw', True),
+         ('p2end', OM_PHASE2END)
+      ])
+   ]
+)
+
 encode_map(O_ADD64_32,
    encodings=[
       (I_INT32_64_EXT, [
@@ -1082,6 +1094,52 @@ group_map(O_UNPCK,
    dests=[('w[0]', ('0', DEST(0)), 'ft0')]
 )
 
+group_map(O_MOVWM,
+   hdr=(I_IGRP_HDR_MAIN, [
+      ('oporg', 'p0_p2'),
+      ('olchk', OM_OLCHK),
+      ('w1p', False),
+      ('w0p', True),
+      ('cc', OM_EXEC_CND),
+      ('end', OM_END),
+      ('atom', OM_ATOM),
+      ('rpt', OM_RPT)
+   ]),
+   enc_ops=[
+      ('0', O_MBYP, ['ft0'], [SRC(0)]),
+      ('2_mov', O_MOVWM, [DEST(0)], ['ft0', SRC(1)], [(OM_PHASE2END, OM_PHASE2END)])
+   ],
+   srcs=[
+      ('s[0]', ('0', SRC(0)), 's0'),
+      ('s[1]', ('2_mov', SRC(1)), 'is4')
+   ],
+   iss=[
+      ('is[0]', 's1'),
+      ('is[4]', 'fte')
+   ],
+   dests=[('w[0]', ('2_mov', DEST(0)), 'w0')]
+)
+
+group_map(O_MOVS1,
+   hdr=(I_IGRP_HDR_MAIN, [
+      ('oporg', 'p2'),
+      ('olchk', OM_OLCHK),
+      ('w1p', False),
+      ('w0p', True),
+      ('cc', OM_EXEC_CND),
+      ('end', OM_END),
+      ('atom', OM_ATOM),
+      ('rpt', OM_RPT)
+   ]),
+   enc_ops=[('2_mov', O_MOVWM, [DEST(0)], [SRC(0), 'is4'], [(OM_PHASE2END, True)])],
+   srcs=[('s[1]', ('2_mov', SRC(0)), 'fte')],
+   iss=[
+      ('is[0]', 's1'),
+      ('is[4]', 'fte')
+   ],
+   dests=[('w[0]', ('2_mov', DEST(0)), 'w0')]
+)
+
 group_map(O_ADD64_32,
    hdr=(I_IGRP_HDR_MAIN, [
       ('oporg', 'p0'),
diff --git a/src/imagination/pco/pco_ops.py b/src/imagination/pco/pco_ops.py
index 60ad90b29da..d9748d87257 100644
--- a/src/imagination/pco/pco_ops.py
+++ b/src/imagination/pco/pco_ops.py
@@ -303,6 +303,9 @@ O_UNPCK = hw_op('unpck', OM_ALU + [OM_PCK_FMT, OM_ROUNDZERO, OM_SCALE], 1, 1, []
 O_TST = hw_direct_op('tst', [OM_TST_OP_MAIN, OM_PHASE2END, OM_TST_TYPE_MAIN], 2, 2, [], [[RM_ELEM], [RM_ELEM]])
 O_MOVC = hw_direct_op('movc', [OM_PHASE2END], 2, 5, [[RM_ELEM]])
 
+O_MOVWM = hw_op('movwm', OM_ALU + [OM_PHASE2END], 1, 2, [[RM_ELEM]])
+O_MOVS1 = hw_op('movs1', OM_ALU, 1, 1)
+
 # TODO
 # O_PCK_ELEM = pseudo_op('pck.elem', OM_ALU_RPT1 + [OM_PCK_FMT, OM_ROUNDZERO, OM_SCALE], 1, 2)
 
diff --git a/src/imagination/pco/pco_validate.c b/src/imagination/pco/pco_validate.c
index a9b205c21a4..0f432472798 100644
--- a/src/imagination/pco/pco_validate.c
+++ b/src/imagination/pco/pco_validate.c
@@ -152,12 +152,85 @@ static void pco_validate_ssa(struct val_state *state)
                        "SSA destination defined to more than once");
             BITSET_SET(ssa_writes, pdest->val);
          }
+
+         state->instr = NULL;
+         state->cf_node = NULL;
       }
 
       ralloc_free(ssa_writes);
 
       state->func = NULL;
       state->ref = NULL;
+      state->ref_cursor = REF_CURSOR_NONE;
+   }
+}
+
+/**
+ * \brief Validates hardware source mappings.
+ *
+ * \param[in,out] state Validation state.
+ */
+static void pco_validate_src_maps(struct val_state *state)
+{
+   /* Only check after the legalize pass has run. */
+   if (!state->shader->is_legalized)
+      return;
+
+   bool needs_s124;
+   pco_foreach_func_in_shader (func, state->shader) {
+      state->func = func;
+
+      pco_foreach_instr_in_func (instr, func) {
+         const struct pco_op_info *info = &pco_op_info[instr->op];
+         if (info->type == PCO_OP_TYPE_PSEUDO)
+            continue;
+
+         state->cf_node = &instr->parent_block->cf_node;
+         state->instr = instr;
+
+         state->ref_cursor = REF_CURSOR_INSTR_DEST;
+         pco_foreach_instr_dest (pdest, instr) {
+            state->ref = pdest;
+            unsigned dest_index = pdest - instr->dest;
+
+            if (!info->dest_intrn_map[dest_index])
+               continue;
+
+            enum pco_io mapped_src =
+               PCO_IO_S0 + info->dest_intrn_map[dest_index] - 1;
+
+            bool valid = ref_src_map_valid(*pdest, mapped_src, &needs_s124);
+            PCO_ASSERT(state,
+                       valid,
+                       "HW register reference should be mapped to %s",
+                       needs_s124 ? "S1/S2/S4" : "S0/S2/S3");
+         }
+
+         state->ref_cursor = REF_CURSOR_INSTR_SRC;
+         pco_foreach_instr_src (psrc, instr) {
+            state->ref = psrc;
+            unsigned src_index = psrc - instr->src;
+
+            if (!info->src_intrn_map[src_index])
+               continue;
+
+            enum pco_io mapped_src =
+               PCO_IO_S0 + info->src_intrn_map[src_index] - 1;
+
+            bool valid = ref_src_map_valid(*psrc, mapped_src, &needs_s124);
+            PCO_ASSERT(state,
+                       valid,
+                       "HW register reference should be mapped to %s",
+                       needs_s124 ? "S1/S2/S4" : "S0/S2/S3");
+         }
+
+         state->instr = NULL;
+         state->cf_node = NULL;
+      }
+
+      state->func = NULL;
+      state->ref = NULL;
+      state->ref_cursor = REF_CURSOR_NONE;
    }
 }
 
@@ -179,8 +252,10 @@ void pco_validate_shader(UNUSED pco_shader *shader, UNUSED const char *when)
       .phase = -1,
    };
 
-   if (!shader->is_grouped)
+   if (!shader->is_grouped) {
       pco_validate_ssa(&state);
+      pco_validate_src_maps(&state);
+   }
 
    puts("finishme: pco_validate_shader");
 #endif /* NDEBUG */