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The Java backend was sometimes generating code like this to initialise RTTI
data structures:
foo_type_info.init(...,
/* cast */ new TypeInfo_Struct(bar_type_ctor_info), ...);
bar_type_ctor_info.init(...);
where `bar_type_ctor_info' is actually a type_info.
The problem is that the fields of the non-initialised `bar_type_ctor_info'
would be copied into the new TypeInfo_Struct object. The "cast" is of course
also unnecessary as the bar is already a TypeInfo_Struct.
This patch attempts to fix the problem in two ways:
1. Don't allocate a new TypeInfo_Struct object to emulate the "cast" unless the
value is actually a TypeCtorInfo_Struct, avoiding the problem of copying
uninitialised fields. Currently this is implemented by a runtime check because
the MLDS `cast' operation doesn't record the original type of the value being
cast.
2. Instead of relying on mlds_to_rtti.m to return a list of RTTI data
structures where sub-structures appear before the structures that reference
them, explicitly perform a topological sort. This should be more robust.
Unrelated change: use pre-allocated PseudoTypeInfo instances for common
variable numbers (1 through 5).
compiler/rtti_to_mlds.m:
Add a function to order a list of RTTI definitions as above.
Use cons instead of list.append in some places now that we can.
compiler/mlds_to_java.m:
Call the function to order RTTI definitions before outputing
the initialisations.
Call TypeInfo_Struct.maybe_new instead of allocating new
TypeInfo_Structs.
Generate code that uses pre-allocated PseudoTypeInfo instances.
java/runtime/TypeInfo_Struct.java:
Add a `maybe_new' method for "casting" TypeCtorInfo_Structs to
TypeInfos or returning the argument unchanged.
Delete a copy constructor; now unused.
Add some assertions.
java/runtime/PseudoTypeInfo.java:
Add static instances of PseudoTypeInfo.
tests/hard_coded/Mmakefile:
tests/hard_coded/java_rtti_bug.exp:
tests/hard_coded/java_rtti_bug.m:
Add test case.
34 lines
816 B
Mathematica
34 lines
816 B
Mathematica
% Regression test.
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% The Java backend was generating code that didn't initialise an type_ctor_info
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% before another RTTI structure referenced it. This resulted in a null
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% pointer exception when this program is executed.
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:- module java_rtti_bug.
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:- interface.
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:- import_module io.
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:- pred main(io::di, io::uo) is det.
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%-----------------------------------------------------------------------------%
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%-----------------------------------------------------------------------------%
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:- implementation.
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main(!IO) :-
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X = foo(bar(baz(1))),
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io.write(X, !IO),
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io.nl(!IO).
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:- type foo
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---> foo(bar(baz(int))).
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:- type bar(T)
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---> bar(T).
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:- type baz(T)
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---> baz(T).
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%-----------------------------------------------------------------------------%
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% vim: ft=mercury ts=8 sts=4 sw=4 et
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