ir3: Allow collect sources to be undef

Undef collect sources will never have a move materialized for them.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28447>

src/freedreno/ir3/ir3_context.c

@@ -322,7 +322,19 @@ ir3_create_collect(struct ir3_builder *build,
    if (arrsz == 1)
       return arr[0];
 
-   unsigned flags = dest_flags(arr[0]);
+   int non_undef_src = -1;
+   for (unsigned i = 0; i < arrsz; i++) {
+      if (arr[i]) {
+         non_undef_src = i;
+         break;
+      }
+   }
+
+   /* There should be at least one non-undef source to determine the type of the
+    * destination.
+    */
+   assert(non_undef_src != -1);
+   unsigned flags = dest_flags(arr[non_undef_src]);
 
    collect = ir3_build_instr(build, OPC_META_COLLECT, 1, arrsz);
    __ssa_dst(collect)->flags |= flags;
@@ -353,13 +365,17 @@ ir3_create_collect(struct ir3_builder *build,
        * scalar registers.
        *
        */
-      if (elem->dsts[0]->flags & IR3_REG_ARRAY) {
+      if (elem && elem->dsts[0]->flags & IR3_REG_ARRAY) {
          type_t type = (flags & IR3_REG_HALF) ? TYPE_U16 : TYPE_U32;
          elem = ir3_MOV(build, elem, type);
       }
 
-      assert(dest_flags(elem) == flags);
-      __ssa_src(collect, elem, flags);
+      if (elem) {
+         assert(dest_flags(elem) == flags);
+         __ssa_src(collect, elem, flags);
+      } else {
+         ir3_src_create(collect, INVALID_REG, flags | IR3_REG_SSA);
+      }
    }
 
    collect->dsts[0]->wrmask = MASK(arrsz);

src/freedreno/ir3/ir3_lower_parallelcopy.c

@@ -520,12 +520,15 @@ ir3_lower_copies(struct ir3_shader_variant *v)
             unsigned flags = dst->flags & (IR3_REG_HALF | IR3_REG_SHARED);
             for (unsigned i = 0; i < instr->srcs_count; i++) {
                struct ir3_register *src = instr->srcs[i];
-               array_insert(NULL, copies,
-                            (struct copy_entry){
-                               .dst = ra_num_to_physreg(dst->num + i, flags),
-                               .src = get_copy_src(src, 0),
-                               .flags = flags,
-                            });
+               if ((src->flags & (IR3_REG_CONST | IR3_REG_IMMED)) ||
+                   src->num != INVALID_REG) {
+                  array_insert(NULL, copies,
+                               (struct copy_entry){
+                                  .dst = ra_num_to_physreg(dst->num + i, flags),
+                                  .src = get_copy_src(src, 0),
+                                  .flags = flags,
+                               });
+               }
             }
             handle_copies(v, instr, copies, copies_count);
             list_del(&instr->node);

src/freedreno/ir3/ir3_merge_regs.c

@@ -377,7 +377,8 @@ aggressive_coalesce_collect(struct ir3_liveness *live,
 {
    for (unsigned i = 0, offset = 0; i < collect->srcs_count;
         offset += reg_elem_size(collect->srcs[i]), i++) {
-      if (!(collect->srcs[i]->flags & IR3_REG_SSA))
+      if (!(collect->srcs[i]->flags & IR3_REG_SSA) ||
+          !collect->srcs[i]->def)
          continue;
       try_merge_defs(live, collect->dsts[0], collect->srcs[i]->def, offset);
    }