ir3: Copy-propagate single-source phis

These can be created when removing unreachable control flow, and it
seems easier to remove them than to add special code to handle them when
spilling.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12033>

src/freedreno/ir3/ir3.h

@@ -801,6 +801,8 @@ is_same_type_mov(struct ir3_instruction *instr)
       if (!is_same_type_reg(instr->dsts[0], instr->srcs[0]))
          return false;
       break;
+   case OPC_META_PHI:
+      return instr->srcs_count == 1;
    default:
       return false;
    }

src/freedreno/ir3/ir3_cp.c

@@ -536,11 +536,12 @@ instr_cp(struct ir3_cp_ctx *ctx, struct ir3_instruction *instr)
          /* TODO non-indirect access we could figure out which register
           * we actually want and allow cp..
           */
-         if (reg->flags & IR3_REG_ARRAY)
+         if ((reg->flags & IR3_REG_ARRAY) && src->opc != OPC_META_PHI)
             continue;
 
          /* Don't CP absneg into meta instructions, that won't end well: */
-         if (is_meta(instr) && (src->opc != OPC_MOV))
+         if (is_meta(instr) &&
+             (src->opc == OPC_ABSNEG_F || src->opc == OPC_ABSNEG_S))
             continue;
 
          /* Don't CP mova and mova1 into their users */