[m-rev.] for review: work around bug #142

[Peter Wang]

I don't know what the proper fix should be.


Branches: main, 10.04

Work around bug #142.  The symptom is an assertion failure in
hlds.hlds_rtti.apply_substs_to_constraint_map.  It occurs when:

- a variable holding a typeclass_info is used multiple times in a call;
- the called procedure is inlined into the caller;
- the corresponding head variables have class constraints with functional
  dependencies;
- the type variables in those constraints should be unified, but type variables
  in the ranges of functional dependencies are not unified;
- a single typeclass_info variable ends up being for two different constraints.

The work around adopted here is to prevent inlining of a call when a single
typeclass_info variable appears multiple times in the argument list, for which
the head variables have differing class constraints.

compiler/inlining.m:
        As above.

tests/valid/Mercury.options:
tests/valid/Mmakefile:
tests/valid/bug142.m:
        Add test case.

diff --git a/compiler/inlining.m b/compiler/inlining.m
index 87574a3..1e04d3f 100644
--- a/compiler/inlining.m
+++ b/compiler/inlining.m
@@ -169,6 +169,7 @@
 :- import_module int.
 :- import_module list.
 :- import_module maybe.
+:- import_module multi_map.
 :- import_module pair.
 :- import_module set.
 :- import_module svset.
@@ -647,7 +648,9 @@ inlining_in_call(PredId, ProcId, ArgVars, Builtin,
             list.length(CalleeListOfVars, CalleeThisMany),
             TotalVars = ThisMany + CalleeThisMany,
             TotalVars =< VarThresh
-        )
+        ),
+        % XXX Work around bug #142.
+        not may_encounter_bug_142(ProcInfo, ArgVars)
     ->
         do_inline_call(HeadTypeParams, ArgVars, PredInfo, ProcInfo,
             VarSet0, VarSet, VarTypes0, VarTypes, TypeVarSet0, TypeVarSet,
@@ -699,6 +702,33 @@ inlining_in_call(PredId, ProcId, ArgVars, Builtin,
         GoalInfo = GoalInfo0
     ).
 
+:- pred may_encounter_bug_142(proc_info::in, list(prog_var)::in) is semidet.
+
+may_encounter_bug_142(CalleeProcInfo, ArgVars) :-
+    proc_info_get_rtti_varmaps(CalleeProcInfo, RttiVarMaps),
+    proc_info_get_headvars(CalleeProcInfo, HeadVars),
+    multi_map.from_corresponding_lists(ArgVars, HeadVars, MultiMap),
+    some [ArgVar] (
+        list.member(ArgVar, ArgVars),
+        multi_map.lookup(MultiMap, ArgVar, HeadVarsForArgVar),
+        HeadVarsForArgVar = [_ | _],
+        tci_vars_different_constraints(RttiVarMaps, HeadVarsForArgVar)
+    ).
+
+:- pred tci_vars_different_constraints(rtti_varmaps::in, list(prog_var)::in)
+    is semidet.
+
+tci_vars_different_constraints(RttiVarMaps, [VarA, VarB | Vars]) :-
+    (
+        rtti_varmaps_var_info(RttiVarMaps, VarA, VarInfoA),
+        rtti_varmaps_var_info(RttiVarMaps, VarB, VarInfoB),
+        VarInfoA = typeclass_info_var(ConstraintA),
+        VarInfoB = typeclass_info_var(ConstraintB),
+        ConstraintA \= ConstraintB
+    ;
+        tci_vars_different_constraints(RttiVarMaps, [VarB | Vars])
+    ).
+
 %-----------------------------------------------------------------------------%
 
 do_inline_call(HeadTypeParams, ArgVars, PredInfo, ProcInfo,
diff --git a/tests/valid/Mercury.options b/tests/valid/Mercury.options
index 4718a74..bc84b5f 100644
--- a/tests/valid/Mercury.options
+++ b/tests/valid/Mercury.options
@@ -41,6 +41,7 @@ MCFLAGS-builtin_false		= --intermodule-optimization
 MCFLAGS-bug85			= -O0 --deforestation
 MCFLAGS-bug100                  = --halt-at-warn
 MCFLAGS-bug134                  = --no-static-ground-terms --no-optimize-dead-procs
+MCFLAGS-bug142                  = --optimise-higher-order --inline-single-use
 MCFLAGS-compl_unify_bug		= -O3
 MCFLAGS-constraint_prop_bug	= -O0 --common-struct --local-constraint-propagation
 MCFLAGS-csharp_hello		= --no-intermodule-optimization
diff --git a/tests/valid/Mmakefile b/tests/valid/Mmakefile
index 755156f..3871fe2 100644
--- a/tests/valid/Mmakefile
+++ b/tests/valid/Mmakefile
@@ -66,6 +66,7 @@ OTHER_PROGS= \
 	bug85 \
 	bug100 \
 	bug134 \
+	bug142 \
 	builtin_false \
 	call_failure \
 	common_struct_bug \
diff --git a/tests/valid/bug142.m b/tests/valid/bug142.m
new file mode 100644
index 0000000..6a514c9
--- /dev/null
+++ b/tests/valid/bug142.m
@@ -0,0 +1,53 @@
+% Regression test for bug 142.
+%
+% mmc --optimise-higher-order --inline-single-use -C bug142.m
+% Uncaught Mercury exception:
+% Software Error: hlds_rtti.m: Unexpected: inconsistent typeclass_infos
+
+:- module bug142.
+:- interface.
+
+:- type r(T)
+    --->    ok(T)
+    ;       err.
+
+:- type dcg(T, State) == (pred(r(T), State, State)).
+:- mode dcg           == in(pred(out, in, out) is det).
+
+:- typeclass dcg(Token, State) <= ((State -> (Token))) where [
+].
+
+:- pred or(dcg(T, State)::dcg, dcg(T, State)::dcg,
+    r(T)::out, State::in, State::out) is det <= dcg(Token, State).
+
+:- pred orr(dcg(T, State)::dcg, dcg(T, State)::dcg, dcg(T, State)::dcg,
+    r(T)::out, State::in, State::out) is det <= dcg(Token, State).
+
+%------------------------------------------------------------------------------%
+%------------------------------------------------------------------------------%
+
+:- implementation.
+
+or(PA, PB, Result, S0, S) :-
+    PA(RA, S0, S1),
+    (
+        RA = ok(V),
+        S = S1,
+        Result = ok(V)
+    ;
+        RA = err,
+        PB(RB, S0, S),
+        (
+            RB = ok(V),
+            Result = ok(V)
+        ;
+            RB = err,
+            Result = err
+        )
+    ).
+
+orr(PA, PB, PC, Result, S0, S) :-
+    or(or(PA, PB), PC, Result, S0, S).
+
+%------------------------------------------------------------------------------%
+% vim: ft=mercury ts=4 sw=4 et

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