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The Java backend was sometimes generating code like this to initialise RTTI

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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.
This commit is contained in:
Peter Wang
2009-06-26 01:12:00 +00:00
parent aa898ab5dc
commit 6be2fe20ee
7 changed files with 296 additions and 49 deletions
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12
java/runtime/PseudoTypeInfo.java
View File

@@ -1,5 +1,5 @@
//
// Copyright (C) 2001-2004 The University of Melbourne.
// Copyright (C) 2001-2004, 2009 The University of Melbourne.
// This file may only be copied under the terms of the GNU Library General
// Public License - see the file COPYING.LIB in the Mercury distribution.
//
@@ -26,6 +26,14 @@ public class PseudoTypeInfo {
public PseudoTypeInfo(int n) { variable_number = n; }
protected PseudoTypeInfo() { variable_number = -1; }
// Adding or removing members requires corresponding changes in
// mlds_to_java.m.
public static final PseudoTypeInfo K1 = new PseudoTypeInfo(1);
public static final PseudoTypeInfo K2 = new PseudoTypeInfo(2);
public static final PseudoTypeInfo K3 = new PseudoTypeInfo(3);
public static final PseudoTypeInfo K4 = new PseudoTypeInfo(4);
public static final PseudoTypeInfo K5 = new PseudoTypeInfo(5);
// XXX This should be renamed `equals'
public boolean unify(PseudoTypeInfo ti) {
if (this.getClass() == TypeInfo_Struct.class &&
@@ -36,3 +44,5 @@ public class PseudoTypeInfo {
return variable_number == ti.variable_number;
}
}
// vim: set ts=8 sts=8 sw=8 noet: