`llzk-unused-declaration-elim` can remove struct members that still have read/write

[tim-hoffman]

Run:

llzk-opt -llzk-unused-declaration-elim -debug-only=llzk-unused-declaration-elim <input>

Input:

module attributes {llzk.lang, llzk.main = !struct.type<@std::@C1>} {
  module @std attributes {llzk.lang = "zirgen"} {
    module @std attributes {llzk.lang = "zirgen"} {
      module @risc0 {
        struct.def @ValU32 {
          struct.member @low : !felt.type {llzk.pub}
          struct.member @high : !felt.type {llzk.pub}
          function.def @compute(%arg0: !felt.type, %arg1: !felt.type) -> !struct.type<@risc0::@ValU32> attributes {function.allow_witness} {
            %self = struct.new : <@risc0::@ValU32>
            struct.writem %self[@low] = %arg0 : <@risc0::@ValU32>, !felt.type
            struct.writem %self[@high] = %arg1 : <@risc0::@ValU32>, !felt.type
            function.return %self : !struct.type<@risc0::@ValU32>
          }
          function.def @constrain(%arg0: !struct.type<@risc0::@ValU32>, %arg1: !felt.type, %arg2: !felt.type) attributes {function.allow_constraint} {
            function.return
          }
        }
        struct.def @Reg {
          struct.member @reg : !felt.type {llzk.pub}
          function.def @compute(%arg0: !felt.type) -> !struct.type<@risc0::@Reg> attributes {function.allow_witness} {
            %self = struct.new : <@risc0::@Reg>
            struct.writem %self[@reg] = %arg0 : <@risc0::@Reg>, !felt.type
            function.return %self : !struct.type<@risc0::@Reg>
          }
          function.def @constrain(%arg0: !struct.type<@risc0::@Reg>, %arg1: !felt.type) attributes {function.allow_constraint} {
            %0 = struct.readm %arg0[@reg] : <@risc0::@Reg>, !felt.type
            constrain.eq %arg1, %0 : !felt.type, !felt.type
            function.return
          }
        }
      }
    }
    struct.def @C1 {
      struct.member @z : !struct.type<@std::@risc0::@Reg> {llzk.pub}
      function.def @compute(%arg0: !felt.type, %arg1: !felt.type) -> !struct.type<@C1> attributes {function.allow_witness} {
        %self = struct.new : <@C1>
        %0 = felt.add %arg0, %arg1 : !felt.type, !felt.type
        %1 = function.call @std::@risc0::@Reg::@compute(%0) : (!felt.type) -> !struct.type<@std::@risc0::@Reg>
        struct.writem %self[@z] = %1 : <@C1>, !struct.type<@std::@risc0::@Reg>
        function.return %self : !struct.type<@C1>
      }
      function.def @constrain(%arg0: !struct.type<@C1>, %arg1: !felt.type, %arg2: !felt.type) attributes {function.allow_constraint} {
        %0 = struct.readm %arg0[@z] : <@C1>, !struct.type<@std::@risc0::@Reg>
        %1 = felt.add %arg1, %arg2 : !felt.type, !felt.type
        function.call @std::@risc0::@Reg::@constrain(%0, %1) : (!struct.type<@std::@risc0::@Reg>, !felt.type) -> ()
        function.return
      }
    }
  }
}

Output:

Removing member struct.member @high : !felt.type {llzk.pub}
Removing member "struct.member"() <{sym_name = "low", type = !felt.type}> {llzk.pub} : () -> ()
Removing member struct.member @reg : !felt.type {llzk.pub}
Removing member struct.member @z : !struct.type<@std::@risc0::@Reg> {llzk.pub}
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:15:13: error: 'struct.writem' op references unknown symbol "@low"
            struct.writem %self[@low] = %arg0 : <@risc0::@ValU32>, !felt.type
            ^
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:15:13: note: see current operation: "struct.writem"(%0, %arg0) <{member_name = @low}> : (!struct.type<@risc0::@ValU32>, !felt.type) -> ()
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:15:13: error: could not find 'struct.member' named "@low" in "@risc0::@ValU32"
            struct.writem %self[@low] = %arg0 : <@risc0::@ValU32>, !felt.type
            ^
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:15:13: note: see current operation: "struct.writem"(%0, %arg0) <{member_name = @low}> : (!struct.type<@risc0::@ValU32>, !felt.type) -> ()
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:31:18: error: 'struct.readm' op references unknown symbol "@reg"
            %0 = struct.readm %arg0[@reg] : <@risc0::@Reg>, !felt.type
                 ^
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:31:18: note: see current operation: %0 = "struct.readm"(%arg0) <{mapOpGroupSizes = array<i32>, member_name = @reg, numDimsPerMap = array<i32>}> : (!struct.type<@risc0::@Reg>) -> !felt.type
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:31:18: error: could not find 'struct.member' named "@reg" in "@risc0::@Reg"
            %0 = struct.readm %arg0[@reg] : <@risc0::@Reg>, !felt.type
                 ^
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:31:18: note: see current operation: %0 = "struct.readm"(%arg0) <{mapOpGroupSizes = array<i32>, member_name = @reg, numDimsPerMap = array<i32>}> : (!struct.type<@risc0::@Reg>) -> !felt.type
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:48:14: error: 'struct.readm' op references unknown symbol "@z"
        %0 = struct.readm %arg0[@z] : <@C1>, !struct.type<@std::@risc0::@Reg>
             ^
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:48:14: note: see current operation: %0 = "struct.readm"(%arg0) <{mapOpGroupSizes = array<i32>, member_name = @z, numDimsPerMap = array<i32>}> : (!struct.type<@C1>) -> !struct.type<@std::@risc0::@Reg>
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:48:14: error: could not find 'struct.member' named "@z" in "@C1"
        %0 = struct.readm %arg0[@z] : <@C1>, !struct.type<@std::@risc0::@Reg>
             ^
~/llzk-lib/test/Transforms/RedundantAndUnusedElim/redundant_op_pass_C.llzk:48:14: note: see current operation: %0 = "struct.readm"(%arg0) <{mapOpGroupSizes = array<i32>, member_name = @z, numDimsPerMap = array<i32>}> : (!struct.type<@C1>) -> !struct.type<@std::@risc0::@Reg>