diff --git a/compiler/arg_info.m b/compiler/arg_info.m
index a27740df6..f0b7b4dbb 100644
--- a/compiler/arg_info.m
+++ b/compiler/arg_info.m
@@ -33,7 +33,6 @@
 :- import_module hlds.hlds_markers.
 :- import_module hlds.hlds_module.
 :- import_module hlds.hlds_proc.
-:- import_module hlds.pred_info_types.
 :- import_module parse_tree.
 :- import_module parse_tree.prog_data.
 :- import_module parse_tree.var_table.
diff --git a/compiler/call_gen.m b/compiler/call_gen.m
index 5ec49e72f..05efffdab 100644
--- a/compiler/call_gen.m
+++ b/compiler/call_gen.m
@@ -21,7 +21,7 @@
 :- import_module hlds.
 :- import_module hlds.code_model.
 :- import_module hlds.hlds_goal.
-:- import_module hlds.pred_info_types.
+:- import_module hlds.hlds_llds.
 :- import_module hlds.pred_proc_id.
 :- import_module libs.
 :- import_module libs.globals.
@@ -76,7 +76,6 @@
 :- import_module backend_libs.builtin_ops.
 :- import_module hlds.arg_info.
 :- import_module hlds.hlds_class.
-:- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_markers.
 :- import_module hlds.hlds_module.
 :- import_module hlds.hlds_pred.
diff --git a/compiler/closure_gen.m b/compiler/closure_gen.m
index 96ba08120..f42ed226b 100644
--- a/compiler/closure_gen.m
+++ b/compiler/closure_gen.m
@@ -47,7 +47,6 @@
 :- import_module hlds.hlds_pred.
 :- import_module hlds.hlds_proc.
 :- import_module hlds.hlds_proc_util.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.type_classify.
 :- import_module libs.
 :- import_module libs.globals.
diff --git a/compiler/code_info.m b/compiler/code_info.m
index 62f261b49..7202c6c9a 100644
--- a/compiler/code_info.m
+++ b/compiler/code_info.m
@@ -33,7 +33,6 @@
 :- import_module hlds.hlds_module.
 :- import_module hlds.hlds_pred.
 :- import_module hlds.hlds_proc.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module libs.
 :- import_module libs.globals.
diff --git a/compiler/code_loc_dep.m b/compiler/code_loc_dep.m
index a32b36e61..1b77ad7d5 100644
--- a/compiler/code_loc_dep.m
+++ b/compiler/code_loc_dep.m
@@ -46,7 +46,6 @@
 :- import_module hlds.hlds_goal.
 :- import_module hlds.hlds_llds.
 :- import_module hlds.instmap.
-:- import_module hlds.pred_info_types.
 :- import_module libs.
 :- import_module libs.options.
 :- import_module ll_backend.code_info.
@@ -195,7 +194,7 @@ code_loc_dep_init(FollowVars, ResumePoint, !CI, !:CLD) :-
     get_proc_info(!.CI, ProcInfo),
     module_info_get_globals(ModuleInfo, Globals),
     proc_info_get_initial_instmap(ModuleInfo, ProcInfo, InstMap),
-    proc_info_get_liveness_info(ProcInfo, Liveness),
+    proc_info_get_initial_liveness(ProcInfo, Liveness),
     CodeModel = proc_info_interface_code_model(ProcInfo),
     build_input_arg_list(ProcInfo, ArgList),
     get_var_table(!.CI, VarTable),
diff --git a/compiler/code_util.m b/compiler/code_util.m
index 09b61540a..5beecf946 100644
--- a/compiler/code_util.m
+++ b/compiler/code_util.m
@@ -21,7 +21,6 @@
 :- import_module hlds.hlds_module.
 :- import_module hlds.hlds_proc.
 :- import_module hlds.hlds_rtti.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module libs.
 :- import_module libs.optimization_options.
diff --git a/compiler/continuation_info.m b/compiler/continuation_info.m
index 3a72e1321..3f72c123b 100644
--- a/compiler/continuation_info.m
+++ b/compiler/continuation_info.m
@@ -54,12 +54,12 @@
 
 :- import_module hlds.
 :- import_module hlds.hlds_goal.
+:- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_module.
 :- import_module hlds.hlds_pred.
 :- import_module hlds.hlds_proc.
 :- import_module hlds.hlds_rtti.
 :- import_module hlds.instmap.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module hlds.proc_info_types.
 :- import_module libs.
@@ -417,7 +417,6 @@
 
 :- implementation.
 
-:- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_proc_util.
 :- import_module libs.options.
 :- import_module ll_backend.code_util.
diff --git a/compiler/deep_profiling.m b/compiler/deep_profiling.m
index 6bdc83ba6..09e6da063 100644
--- a/compiler/deep_profiling.m
+++ b/compiler/deep_profiling.m
@@ -81,7 +81,6 @@
 :- import_module hlds.instmap.
 :- import_module hlds.make_goal.
 :- import_module hlds.mode_top_functor.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_name.
 :- import_module hlds.pred_table.
 :- import_module hlds.proc_info_types.
diff --git a/compiler/export.m b/compiler/export.m
index 2788eb165..b864c31d1 100644
--- a/compiler/export.m
+++ b/compiler/export.m
@@ -19,8 +19,8 @@
 :- interface.
 
 :- import_module hlds.
+:- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_module.
-:- import_module hlds.pred_info_types.
 :- import_module parse_tree.
 :- import_module parse_tree.prog_data.
 :- import_module parse_tree.prog_foreign.
@@ -92,7 +92,6 @@
 :- import_module hlds.arg_info.
 :- import_module hlds.code_model.
 :- import_module hlds.hlds_data.
-:- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_pred.
 :- import_module hlds.hlds_proc.
 :- import_module hlds.hlds_proc_util.
diff --git a/compiler/fact_table_gen.m b/compiler/fact_table_gen.m
index 8db58171a..d525a5798 100644
--- a/compiler/fact_table_gen.m
+++ b/compiler/fact_table_gen.m
@@ -138,7 +138,6 @@
 :- import_module hlds.inst_test.
 :- import_module hlds.mode_test.
 :- import_module hlds.mode_util.
-:- import_module hlds.pred_info_types.
 :- import_module libs.
 :- import_module libs.file_util.
 :- import_module libs.globals.
diff --git a/compiler/follow_vars.m b/compiler/follow_vars.m
index 6a39d3642..ed59915ed 100644
--- a/compiler/follow_vars.m
+++ b/compiler/follow_vars.m
@@ -58,7 +58,6 @@
 :- import_module hlds.code_model.
 :- import_module hlds.hlds_pred.
 :- import_module hlds.hlds_proc_util.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module ll_backend.call_gen.
 :- import_module parse_tree.prog_data.
diff --git a/compiler/foreign_proc_gen.m b/compiler/foreign_proc_gen.m
index c992915a9..8b65e558d 100644
--- a/compiler/foreign_proc_gen.m
+++ b/compiler/foreign_proc_gen.m
@@ -72,7 +72,6 @@
 :- import_module hlds.hlds_pred.
 :- import_module hlds.instmap.
 :- import_module hlds.mode_top_functor.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.type_util.
 :- import_module libs.
 :- import_module libs.globals.
diff --git a/compiler/hlds_clauses.m b/compiler/hlds_clauses.m
index a817804f6..799ed4e30 100644
--- a/compiler/hlds_clauses.m
+++ b/compiler/hlds_clauses.m
@@ -42,8 +42,9 @@
 :- import_module hlds.hlds_args.
 :- import_module hlds.hlds_goal.
 :- import_module hlds.hlds_rtti.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
+:- import_module libs.
+:- import_module libs.globals.
 :- import_module mdbcomp.
 :- import_module mdbcomp.prim_data.
 :- import_module parse_tree.
@@ -146,6 +147,12 @@
 
 %---------------------%
 
+:- type implementation_language
+    --->    impl_lang_mercury
+    ;       impl_lang_foreign(foreign_language).
+
+%---------------------%
+
 :- type clause
     --->    clause(
                 % The modes for which this clause applies.
diff --git a/compiler/hlds_llds.m b/compiler/hlds_llds.m
index daa4c8bd7..44731a9f0 100644
--- a/compiler/hlds_llds.m
+++ b/compiler/hlds_llds.m
@@ -31,6 +31,17 @@
 :- import_module map.
 :- import_module maybe.
 
+%-----------------------------------------------------------------------------%
+
+:- type arg_info
+    --->    arg_info(
+                arg_loc,                    % Stored location.
+                top_functor_mode            % Mode of top functor.
+            ).
+
+:- type arg_loc
+    --->    reg(reg_type, int).
+
     % reg_r are the general purpose registers.
     %
     % reg_f are float registers.
diff --git a/compiler/hlds_proc.m b/compiler/hlds_proc.m
index 9b1e00338..5ca3c3786 100644
--- a/compiler/hlds_proc.m
+++ b/compiler/hlds_proc.m
@@ -23,7 +23,6 @@
 :- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_module.
 :- import_module hlds.hlds_rtti.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module hlds.proc_info_types.
 :- import_module parse_tree.
@@ -104,7 +103,7 @@
     has_user_event::out, has_tail_rec_call::out, list(oisu_pred_kind_for)::out,
     maybe(require_tail_recursion)::out, set_of_progvar::out,
     maybe(list(arg_info))::out, maybe(special_proc_return)::out,
-    liveness_info::out, stack_slots::out, needs_maxfr_slot::out,
+    codegen_liveness::out, stack_slots::out, needs_maxfr_slot::out,
     maybe(prog_var)::out, maybe(proc_table_io_info)::out,
     maybe(table_attributes)::out, maybe(list(sym_name_arity))::out,
     maybe(deep_profile_proc_info)::out, maybe(arg_size_info)::out,
@@ -125,7 +124,7 @@
     has_user_event::in, has_tail_rec_call::in, list(oisu_pred_kind_for)::in,
     maybe(require_tail_recursion)::in, set_of_progvar::in,
     maybe(list(arg_info))::in, maybe(special_proc_return)::in,
-    liveness_info::in, stack_slots::in, needs_maxfr_slot::in,
+    codegen_liveness::in, stack_slots::in, needs_maxfr_slot::in,
     maybe(prog_var)::in, maybe(proc_table_io_info)::in,
     maybe(table_attributes)::in, maybe(list(sym_name_arity))::in,
     maybe(deep_profile_proc_info)::in, maybe(arg_size_info)::in,
@@ -235,7 +234,8 @@
     maybe(list(arg_info))::out) is det.
 :- pred proc_info_get_maybe_special_return(proc_info::in,
     maybe(special_proc_return)::out) is det.
-:- pred proc_info_get_liveness_info(proc_info::in, liveness_info::out) is det.
+:- pred proc_info_get_initial_liveness(proc_info::in,
+    codegen_liveness::out) is det.
 :- pred proc_info_get_stack_slots(proc_info::in, stack_slots::out) is det.
 :- pred proc_info_get_needs_maxfr_slot(proc_info::in,
     needs_maxfr_slot::out) is det.
@@ -319,7 +319,7 @@
     proc_info::in, proc_info::out) is det.
 :- pred proc_info_set_maybe_special_return(maybe(special_proc_return)::in,
     proc_info::in, proc_info::out) is det.
-:- pred proc_info_set_liveness_info(liveness_info::in,
+:- pred proc_info_set_initial_liveness(codegen_liveness::in,
     proc_info::in, proc_info::out) is det.
 :- pred proc_info_set_stack_slots(stack_slots::in,
     proc_info::in, proc_info::out) is det.
@@ -1025,7 +1025,7 @@ proc_info_reset_imported_structure_reuse(!ProcInfo) :-
                 psi_maybe_special_return        :: maybe(special_proc_return),
 
                 % The initial liveness, for code generation.
-                psi_initial_liveness            :: liveness_info,
+                psi_initial_liveness            :: codegen_liveness,
 
                 % Allocation of variables to stack slots.
                 psi_stack_slots                 :: stack_slots,
@@ -1185,7 +1185,7 @@ proc_info_get_maybe_arg_info(PI, X) :-
     X = PI ^ proc_sub_info ^ psi_maybe_arg_info.
 proc_info_get_maybe_special_return(PI, X) :-
     X = PI ^ proc_sub_info ^ psi_maybe_special_return.
-proc_info_get_liveness_info(PI, X) :-
+proc_info_get_initial_liveness(PI, X) :-
     X = PI ^ proc_sub_info ^ psi_initial_liveness.
 proc_info_get_stack_slots(PI, X) :-
     X = PI ^ proc_sub_info ^ psi_stack_slots.
@@ -1271,7 +1271,7 @@ proc_info_set_arg_info(X, !PI) :-
     !PI ^ proc_sub_info ^ psi_maybe_arg_info := yes(X).
 proc_info_set_maybe_special_return(X, !PI) :-
     !PI ^ proc_sub_info ^ psi_maybe_special_return := X.
-proc_info_set_liveness_info(X, !PI) :-
+proc_info_set_initial_liveness(X, !PI) :-
     !PI ^ proc_sub_info ^ psi_initial_liveness := X.
 proc_info_set_stack_slots(X, !PI) :-
     !PI ^ proc_sub_info ^ psi_stack_slots := X.
diff --git a/compiler/hlds_proc_util.m b/compiler/hlds_proc_util.m
index 90cf78470..fcda2c10a 100644
--- a/compiler/hlds_proc_util.m
+++ b/compiler/hlds_proc_util.m
@@ -17,11 +17,11 @@
 
 :- import_module check_hlds.
 :- import_module check_hlds.mode_constraint_robdd.
+:- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_module.
 :- import_module hlds.hlds_pred.
 :- import_module hlds.hlds_proc.
 :- import_module hlds.instmap.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module parse_tree.
 :- import_module parse_tree.prog_data.
diff --git a/compiler/hlds_rtti.m b/compiler/hlds_rtti.m
index ee9a7cc35..7dbc35362 100644
--- a/compiler/hlds_rtti.m
+++ b/compiler/hlds_rtti.m
@@ -19,7 +19,6 @@
 :- interface.
 
 :- import_module hlds.hlds_module.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_name.
 :- import_module hlds.pred_proc_id.
 :- import_module mdbcomp.
diff --git a/compiler/instance_method_clauses.m b/compiler/instance_method_clauses.m
index 1439ecaac..d90013151 100644
--- a/compiler/instance_method_clauses.m
+++ b/compiler/instance_method_clauses.m
@@ -49,7 +49,6 @@
 :- import_module hlds.instmap.
 :- import_module hlds.make_hlds.add_clause.
 :- import_module hlds.make_hlds.state_var.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module mdbcomp.sym_name.
 :- import_module parse_tree.maybe_error.
diff --git a/compiler/lco.m b/compiler/lco.m
index 3d4b65295..b740085de 100644
--- a/compiler/lco.m
+++ b/compiler/lco.m
@@ -186,7 +186,6 @@
 :- import_module hlds.instmap.
 :- import_module hlds.mode_top_functor.
 :- import_module hlds.passes_aux.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_name.
 :- import_module hlds.pred_proc_id.
 :- import_module hlds.pred_table.
diff --git a/compiler/liveness.m b/compiler/liveness.m
index 3355a1148..52610f053 100644
--- a/compiler/liveness.m
+++ b/compiler/liveness.m
@@ -204,7 +204,6 @@
 :- import_module hlds.hlds_rtti.
 :- import_module hlds.instmap.
 :- import_module hlds.mode_top_functor.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_name.
 :- import_module hlds.quantification.
 :- import_module libs.
@@ -332,7 +331,7 @@ detect_liveness_proc_2(ModuleInfo, PredId, !ProcInfo) :-
             DebugThisPred, PredId, !.ProcInfo, VarTable, Goal, !IO)
     ),
     proc_info_set_goal(Goal, !ProcInfo),
-    proc_info_set_liveness_info(Liveness0, !ProcInfo).
+    proc_info_set_initial_liveness(Liveness0, !ProcInfo).
 
 :- pred maybe_debug_liveness(module_info::in, string::in, bool::in,
     pred_id::in, proc_info::in, var_table::in, hlds_goal::in,
diff --git a/compiler/mark_tail_calls.m b/compiler/mark_tail_calls.m
index 9347c0f3a..2b0013c15 100644
--- a/compiler/mark_tail_calls.m
+++ b/compiler/mark_tail_calls.m
@@ -219,7 +219,6 @@
 :- import_module hlds.hlds_goal.
 :- import_module hlds.hlds_proc_util.
 :- import_module hlds.mode_top_functor.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.proc_info_types.
 :- import_module hlds.type_util.
 :- import_module libs.options.
diff --git a/compiler/ml_args_util.m b/compiler/ml_args_util.m
index bfc73acaf..0ddbdd21a 100644
--- a/compiler/ml_args_util.m
+++ b/compiler/ml_args_util.m
@@ -20,7 +20,6 @@
 :- import_module hlds.code_model.
 :- import_module hlds.hlds_module.
 :- import_module hlds.hlds_rtti.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module mdbcomp.
 :- import_module mdbcomp.prim_data.
diff --git a/compiler/ml_closure_gen.m b/compiler/ml_closure_gen.m
index b0daac39e..319de91b9 100644
--- a/compiler/ml_closure_gen.m
+++ b/compiler/ml_closure_gen.m
@@ -86,7 +86,6 @@
 :- import_module hlds.hlds_pred.
 :- import_module hlds.hlds_proc.
 :- import_module hlds.mark_tail_calls.          % for ntrcr_program
-:- import_module hlds.pred_info_types.
 :- import_module hlds.type_util.
 :- import_module libs.
 :- import_module libs.globals.
diff --git a/compiler/ml_foreign_proc_gen.m b/compiler/ml_foreign_proc_gen.m
index feaf4503c..c13e4b5d3 100644
--- a/compiler/ml_foreign_proc_gen.m
+++ b/compiler/ml_foreign_proc_gen.m
@@ -51,7 +51,6 @@
 :- import_module hlds.hlds_pred.
 :- import_module hlds.hlds_proc_util.
 :- import_module hlds.mode_top_functor.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.type_util.
 :- import_module libs.
 :- import_module libs.globals.
diff --git a/compiler/ml_proc_gen.m b/compiler/ml_proc_gen.m
index 44fdb35ee..a90001c4e 100644
--- a/compiler/ml_proc_gen.m
+++ b/compiler/ml_proc_gen.m
@@ -50,7 +50,6 @@
 :- import_module hlds.hlds_proc_util.
 :- import_module hlds.mark_tail_calls.
 :- import_module hlds.passes_aux.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module hlds.proc_info_types.
 :- import_module hlds.quantification.
diff --git a/compiler/ml_unify_gen_construct.m b/compiler/ml_unify_gen_construct.m
index 8a08868ca..83d46c451 100644
--- a/compiler/ml_unify_gen_construct.m
+++ b/compiler/ml_unify_gen_construct.m
@@ -91,7 +91,6 @@
 :- import_module hlds.hlds_code_util.
 :- import_module hlds.hlds_data.
 :- import_module hlds.mode_top_functor.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module hlds.type_classify.
 :- import_module hlds.type_util.
diff --git a/compiler/ml_unify_gen_util.m b/compiler/ml_unify_gen_util.m
index 0833ef19f..3865d2be5 100644
--- a/compiler/ml_unify_gen_util.m
+++ b/compiler/ml_unify_gen_util.m
@@ -217,7 +217,6 @@
 :- import_module backend_libs.builtin_ops.
 :- import_module hlds.hlds_code_util.
 :- import_module hlds.mode_top_functor.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.type_util.
 :- import_module libs.
 :- import_module libs.globals.
diff --git a/compiler/mode_top_functor.m b/compiler/mode_top_functor.m
index 1175335a1..ca94a00eb 100644
--- a/compiler/mode_top_functor.m
+++ b/compiler/mode_top_functor.m
@@ -17,7 +17,6 @@
 :- interface.
 
 :- import_module hlds.hlds_module.
-:- import_module hlds.pred_info_types.
 :- import_module parse_tree.
 :- import_module parse_tree.prog_data.
 
diff --git a/compiler/modecheck_unify.m b/compiler/modecheck_unify.m
index e33a9d41b..901ee7ad1 100644
--- a/compiler/modecheck_unify.m
+++ b/compiler/modecheck_unify.m
@@ -65,7 +65,6 @@
 :- import_module hlds.mode_test.
 :- import_module hlds.mode_top_functor.
 :- import_module hlds.mode_util.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_proc_id.
 :- import_module hlds.type_classify.
 :- import_module hlds.type_util.
diff --git a/compiler/pred_info_types.m b/compiler/pred_info_types.m
index 531ca8243..a9c38b16d 100644
--- a/compiler/pred_info_types.m
+++ b/compiler/pred_info_types.m
@@ -10,22 +10,17 @@
 % File: hlds_pred.m.
 % Main authors: fjh, conway.
 %
-% This module defines the part of the HLDS that deals with predicates
-% and procedures.
+% This module defines types that are specific to fields of pred_infos.
 %
 %---------------------------------------------------------------------------%
 
 :- module hlds.pred_info_types.
 :- interface.
 
-:- import_module hlds.hlds_llds.
-:- import_module libs.
-:- import_module libs.globals.
 :- import_module parse_tree.
 :- import_module parse_tree.prog_data.
 :- import_module parse_tree.prog_data_pragma.
 :- import_module parse_tree.prog_data_rare.
-:- import_module parse_tree.set_of_var.
 
 :- import_module bool.
 :- import_module map.
@@ -34,10 +29,6 @@
 
 %---------------------------------------------------------------------------%
 
-:- type implementation_language
-    --->    impl_lang_mercury
-    ;       impl_lang_foreign(foreign_language).
-
     % A predicate, and the goal inside it, may implement a promise declaration,
     % or it may be an ordinary predicate.
 :- type goal_type
@@ -51,11 +42,11 @@
     %
     % We use this information in two ways.
     %
-    % First, intermod.m needs to know whether a predicate's definition
-    % contains any foreign_procs, because if it does, then it cannot append
-    % variable numbers after variable names for disambiguation, in e.g. clause
-    % heads, since that would screw up references to those variables in the
-    % foreign code.
+    % First, intermodule optimization needs to know whether a predicate's
+    % definition contains any foreign_procs, because if it does, then
+    % it cannot append variable numbers after variable names for
+    % disambiguation (in e.g. clause heads) since that would screw up
+    % references to those variables in the foreign code.
     %
     % Second, purity.m has special handling for predicates that are defined
     % *only* by foreign procs.
@@ -73,55 +64,10 @@
     ;       np_goal_type_foreign
     ;       np_goal_type_clause_and_foreign.
 
-    % NOTE: `liveness_info' records liveness in the sense used by code
-    % generation. This is *not* the same thing as the notion of liveness
-    % used by mode analysis!  See compiler/notes/glossary.html.
-    %
-:- type liveness_info == set_of_progvar.    % The live variables.
-
-:- type arg_info
-    --->    arg_info(
-                arg_loc,                    % Stored location.
-                top_functor_mode            % Mode of top functor.
-            ).
-
-    % The top_functor_mode specifies the mode of the top-level functor
-    % of a term (excluding `no_tag' functors, since those have no
-    % representation). It is used by the code generators when determining
-    % how to pass the argument.
-    %
-    % For the LLDS back-end, top_in arguments are passed in registers,
-    % and top_out values are returned in registers; top_unused values
-    % are not passed at all, but they are treated as if they were top_out
-    % for the purpose of assigning arguments to registers. (So e.g. if
-    % a det procedure has three arguments with top_functor_modes top_out,
-    % top_unused, and top_out respectively, the last argument will be
-    % returned in register r3, not r2.)
-    %
-    % For the MLDS back-end, top_in values are passed as arguments.
-    % Top_out values are normally passed by reference, except that
-    %   - if the procedure is model_nondet, and the --nondet-copy-out option
-    %     is set, top_out values are passed by value to the continuation
-    %     function;
-    %   - if the procedure is model_det or model_semi, and the
-    %     --det-copy-out option is set, top_out arguments in the HLDS
-    %     are mapped to (multiple) return values in the MLDS; and
-    %   - if the HLDS function return value for a det function has mode
-    %     `top_out', it is mapped to an MLDS return value.
-    % top_unused arguments are not passed at all.
-    %
-:- type top_functor_mode
-    --->    top_in
-    ;       top_out
-    ;       top_unused.
-
-:- type arg_loc
-    --->    reg(reg_type, int).
-
 %---------------------%
 
-    % This type is isomorphic to the module_section type, but defining it here
-    % allows us not to depend on parse_tree.prog_item.m.
+    % This type is isomorphic to the module_section type, but
+    % defining it here allows us not to depend on prog_parse_tree.m.
 :- type decl_section
     --->    decl_interface
     ;       decl_implementation.
@@ -137,6 +83,8 @@
                 item_seq_num
             ).
 
+%---------------------%
+
 :- type format_call_info
     --->    format_call_info(
                 % The context of the format_call pragma whose info
@@ -150,6 +98,8 @@
                 one_or_more(format_string_values)
             ).
 
+%---------------------%
+
     % Mode information for the arguments of a procedure.
     % The first map gives the instantiation state on entry of the node
     % corresponding to the prog_var. The second map gives the instantiation
diff --git a/compiler/proc_info_types.m b/compiler/proc_info_types.m
index 1093d2caa..8259eb03e 100644
--- a/compiler/proc_info_types.m
+++ b/compiler/proc_info_types.m
@@ -10,8 +10,7 @@
 % File: hlds_pred.m.
 % Main authors: fjh, conway.
 %
-% This module defines the part of the HLDS that deals with predicates
-% and procedures.
+% This module defines types that are specific to fields of proc_infos.
 %
 %---------------------------------------------------------------------------%
 
@@ -31,6 +30,7 @@
 :- import_module parse_tree.prog_data.
 :- import_module parse_tree.prog_data_pragma.
 :- import_module parse_tree.prog_data_rare.
+:- import_module parse_tree.set_of_var.
 :- import_module parse_tree.var_table.
 
 :- import_module bool.
@@ -40,6 +40,12 @@
 
 %---------------------------------------------------------------------------%
 
+    % NOTE: `codegen_liveness' records liveness in the sense used by code
+    % generation. This is *not* the same thing as the notion of liveness
+    % used by mode analysis! See compiler/notes/glossary.html.
+    %
+:- type codegen_liveness == set_of_progvar. % The live variables.
+
 :- type is_address_taken
     --->    address_is_taken
     ;       address_is_not_taken.
@@ -118,10 +124,10 @@
     --->    hlds_deep_excp_vars(
                 top_csd                 :: prog_var,
                 middle_csd              :: prog_var,
+
+                % This field is needed only with the save/restore approach,
+                % not the activation counting approach.
                 old_outermost           :: maybe(prog_var)
-                                        % Needed only with the save/restore
-                                        % approach, not the activation counting
-                                        % approach.
             ).
 
 :- type hlds_deep_layout
@@ -312,16 +318,27 @@
                 map(prog_var, list(prog_var))
             ).
 
-:- type detism_decl
-    --->    detism_decl_explicit
-    ;       detism_decl_implicit
-    ;       detism_decl_none.
-            % The determinism of the procedure is not declared.
-
 :- type can_process
     --->    cannot_process_yet
     ;       can_process_now.
 
+    % Values of this type are used only for choosing the wording of
+    % determinism diagnostics.
+:- type detism_decl
+    --->    detism_decl_explicit
+    ;       detism_decl_implicit
+            % The determinism of the procedure is not declared,
+            % but the procedure needs no declaration, because either
+            %
+            % - the procedure is for a function, which are implicitly det
+            %   unless explicitly declared otherwise, or
+            %
+            % - the procedure was created by the compiler, e.g.
+            %   to implement a unify/index/compare predicate,
+            %   to implement an instance method, or as implied mode.
+    ;       detism_decl_none.
+            % The determinism of the procedure is not declared.
+
 :- type needs_maxfr_slot
     --->    needs_maxfr_slot
     ;       does_not_need_maxfr_slot.
diff --git a/compiler/prog_data.m b/compiler/prog_data.m
index 5aeba4345..31b9588d2 100644
--- a/compiler/prog_data.m
+++ b/compiler/prog_data.m
@@ -1661,6 +1661,40 @@ prog_constraint_get_arg_types(Constraint) = Constraint ^ constraint_arg_types.
 :- type from_to_insts
     --->    from_to_insts(mer_inst, mer_inst).
 
+    % The top_functor_mode specifies the mode of the top-level functor
+    % of a term (excluding `no_tag' functors, since those have no
+    % representation). It is used by the code generators when determining
+    % how to pass the argument.
+    %
+    % For the LLDS back-end, top_in arguments are passed in registers,
+    % and top_out values are returned in registers. top_unused values
+    % are not passed at all, but they are treated as if they were top_out
+    % for the purpose of assigning arguments to registers. (So e.g. if
+    % a det procedure has three arguments with top_functor_modes top_out,
+    % top_unused, and top_out respectively, the last argument will be
+    % returned in register r3, not r2.)
+    %
+    % For the MLDS back-end, top_in values are passed as arguments.
+    % Top_out values are normally passed by reference, except that
+    %
+    %   - if the procedure is model_nondet, and the --nondet-copy-out option
+    %     is set, top_out values are passed by value to the continuation
+    %     function;
+    %
+    %   - if the procedure is model_det or model_semi, and the
+    %     --det-copy-out option is set, top_out arguments in the HLDS
+    %     are mapped to (multiple) return values in the MLDS; and
+    %
+    %   - if the HLDS function return value for a det function has mode
+    %     `top_out', it is mapped to an MLDS return value.
+    %
+    % top_unused arguments are not passed at all.
+    %
+:- type top_functor_mode
+    --->    top_in
+    ;       top_out
+    ;       top_unused.
+
 %---------------------------------------------------------------------------%
 %
 % Determinism.
diff --git a/compiler/stack_layout.m b/compiler/stack_layout.m
index dc99c0c7c..14242397b 100644
--- a/compiler/stack_layout.m
+++ b/compiler/stack_layout.m
@@ -111,7 +111,6 @@
 :- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_proc_util.
 :- import_module hlds.hlds_rtti.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.type_util.
 :- import_module libs.
 :- import_module libs.globals.
diff --git a/compiler/structure_reuse.lfu.m b/compiler/structure_reuse.lfu.m
index 454f0e3dd..8de46b06e 100644
--- a/compiler/structure_reuse.lfu.m
+++ b/compiler/structure_reuse.lfu.m
@@ -61,7 +61,7 @@ forward_use_information(!ProcInfo) :-
     proc_info_get_goal(!.ProcInfo, Goal0),
 
     % Set of variables initially instantiated.
-    proc_info_get_liveness_info(!.ProcInfo, InstantiatedVars0),
+    proc_info_get_initial_liveness(!.ProcInfo, InstantiatedVars0),
     % Set of variables initially "dead" = instantiated variables that
     % syntactically do not occur in the remainder of the goal.
     set_of_var.init(DeadVars0),
diff --git a/compiler/structure_sharing.domain.m b/compiler/structure_sharing.domain.m
index 60f415aee..b9cde5110 100644
--- a/compiler/structure_sharing.domain.m
+++ b/compiler/structure_sharing.domain.m
@@ -312,7 +312,6 @@
 :- import_module hlds.inst_test.
 :- import_module hlds.mode_top_functor.
 :- import_module hlds.mode_util.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_name.
 :- import_module hlds.proc_info_types.
 :- import_module hlds.status.
diff --git a/compiler/trace_gen.m b/compiler/trace_gen.m
index 8dd603769..7bc4ee7d1 100644
--- a/compiler/trace_gen.m
+++ b/compiler/trace_gen.m
@@ -51,9 +51,9 @@
 
 :- import_module hlds.
 :- import_module hlds.hlds_goal.
+:- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_module.
 :- import_module hlds.hlds_proc.
-:- import_module hlds.pred_info_types.
 :- import_module libs.
 :- import_module libs.globals.
 :- import_module libs.trace_params.
@@ -246,7 +246,6 @@
 :- import_module backend_libs.
 :- import_module backend_libs.builtin_ops.
 :- import_module hlds.code_model.
-:- import_module hlds.hlds_llds.
 :- import_module hlds.hlds_markers.
 :- import_module hlds.hlds_proc_util.
 :- import_module hlds.inst_test.
diff --git a/compiler/types_into_modes.m b/compiler/types_into_modes.m
index 294371c8f..7f75d4651 100644
--- a/compiler/types_into_modes.m
+++ b/compiler/types_into_modes.m
@@ -52,7 +52,6 @@
 :- import_module hlds.hlds_goal.
 :- import_module hlds.hlds_markers.
 :- import_module hlds.hlds_proc.
-:- import_module hlds.pred_info_types.
 :- import_module libs.
 :- import_module libs.globals.
 :- import_module mdbcomp.
diff --git a/compiler/unify_gen_construct.m b/compiler/unify_gen_construct.m
index b2d7671ea..8cc83b803 100644
--- a/compiler/unify_gen_construct.m
+++ b/compiler/unify_gen_construct.m
@@ -65,7 +65,6 @@
 :- import_module hlds.hlds_data.
 :- import_module hlds.hlds_rtti.
 :- import_module hlds.mode_top_functor.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_name.
 :- import_module hlds.pred_proc_id.
 :- import_module hlds.type_classify.
diff --git a/compiler/unify_gen_util.m b/compiler/unify_gen_util.m
index 1abde448c..94a2944bb 100644
--- a/compiler/unify_gen_util.m
+++ b/compiler/unify_gen_util.m
@@ -93,7 +93,6 @@
 :- import_module backend_libs.
 :- import_module backend_libs.builtin_ops.
 :- import_module hlds.mode_top_functor.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.type_util.
 :- import_module mdbcomp.
 :- import_module mdbcomp.sym_name.
diff --git a/compiler/unify_proc.m b/compiler/unify_proc.m
index b680230ad..f2c50c6d6 100644
--- a/compiler/unify_proc.m
+++ b/compiler/unify_proc.m
@@ -92,7 +92,6 @@
 :- import_module hlds.hlds_rtti.
 :- import_module hlds.instmap.
 :- import_module hlds.make_goal.
-:- import_module hlds.pred_info_types.
 :- import_module hlds.pred_table.
 :- import_module hlds.quantification.
 :- import_module hlds.special_pred.
diff --git a/compiler/var_origins.m b/compiler/var_origins.m
index 95a4cbd96..474237fe0 100644
--- a/compiler/var_origins.m
+++ b/compiler/var_origins.m
@@ -212,7 +212,6 @@
 :- import_module hlds.hlds_clauses.
 :- import_module hlds.hlds_out.
 :- import_module hlds.hlds_out.hlds_out_util.
-:- import_module hlds.pred_info_types.
 :- import_module parse_tree.parse_tree_out_cons_id.
 :- import_module parse_tree.parse_tree_out_info.
 :- import_module parse_tree.parse_tree_out_term.