/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#ifndef SHARE_VM_CODE_DEPENDENCIES_HPP
#define SHARE_VM_CODE_DEPENDENCIES_HPP
#include "ci/ciCallSite.hpp"
#include "ci/ciKlass.hpp"
#include "ci/ciMethodHandle.hpp"
#include "classfile/systemDictionary.hpp"
#include "code/compressedStream.hpp"
#include "code/nmethod.hpp"
#include "utilities/growableArray.hpp"
//** Dependencies represent assertions (approximate invariants) within
// the runtime system, e.g. class hierarchy changes. An example is an
// assertion that a given method is not overridden; another example is
// that a type has only one concrete subtype. Compiled code which
// relies on such assertions must be discarded if they are overturned
// by changes in the runtime system. We can think of these assertions
// as approximate invariants, because we expect them to be overturned
// very infrequently. We are willing to perform expensive recovery
// operations when they are overturned. The benefit, of course, is
// performing optimistic optimizations (!) on the object code.
//
// Changes in the class hierarchy due to dynamic linking or
// class evolution can violate dependencies. There is enough
// indexing between classes and nmethods to make dependency
// checking reasonably efficient.
class ciEnv;
class nmethod;
class OopRecorder;
class xmlStream;
class CompileLog;
class DepChange;
class KlassDepChange;
class CallSiteDepChange;
class No_Safepoint_Verifier;
public:
// Note: In the comments on dependency types, most uses of the terms
// subtype and supertype are used in a "non-strict" or "inclusive"
// sense, and are starred to remind the reader of this fact.
// Strict uses of the terms use the word "proper".
//
// Specifically, every class is its own subtype* and supertype*.
// (This trick is easier than continually saying things like "Y is a
// subtype of X or X itself".)
//
// Sometimes we write X > Y to mean X is a proper supertype of Y.
// The notation X > {Y, Z} means X has proper subtypes Y, Z.
// The notation X.m > Y means that Y inherits m from X, while
// X.m > Y.m means Y overrides X.m. A star denotes abstractness,
// as *I > A, meaning (abstract) interface I is a super type of A,
// or A.*m > B.m, meaning B.m implements abstract method A.m.
//
// In this module, the terms "subtype" and "supertype" refer to
// Java-level reference type conversions, as detected by
// "instanceof" and performed by "checkcast" operations. The method
// Klass::is_subtype_of tests these relations. Note that "subtype"
// is richer than "subclass" (as tested by Klass::is_subclass_of),
// since it takes account of relations involving interface and array
// types.
//
// To avoid needless complexity, dependencies involving array types
// are not accepted. If you need to make an assertion about an
// array type, make the assertion about its corresponding element
// types. Any assertion that might change about an array type can
// be converted to an assertion about its element type.
//
// Most dependencies are evaluated over a "context type" CX, which
// stands for the set Subtypes(CX) of every Java type that is a subtype*
// of CX. When the system loads a new class or interface N, it is
// responsible for re-evaluating changed dependencies whose context
// type now includes N, that is, all super types of N.
//
enum DepType {
end_marker = 0,
// An 'evol' dependency simply notes that the contents of the
// method were used. If it evolves (is replaced), the nmethod
// must be recompiled. No other dependencies are implied.
// A context type CX is a leaf it if has no proper subtype.
// An abstract class CX has exactly one concrete subtype CC.
// The type CX is purely abstract, with no concrete subtype* at all.
// The concrete CX is free of concrete proper subtypes.
// Given a method M1 and a context class CX, the set MM(CX, M1) of
// "concrete matching methods" in CX of M1 is the set of every
// concrete M2 for which it is possible to create an invokevirtual
// or invokeinterface call site that can reach either M1 or M2.
// That is, M1 and M2 share a name, signature, and vtable index.
// We wish to notice when the set MM(CX, M1) is just {M1}, or
// perhaps a set of two {M1,M2}, and issue dependencies on this.
// The set MM(CX, M1) can be computed by starting with any matching
// concrete M2 that is inherited into CX, and then walking the
// subtypes* of CX looking for concrete definitions.
// The parameters to this dependency are the method M1 and the
// context class CX. M1 must be either inherited in CX or defined
// in a subtype* of CX. It asserts that MM(CX, M1) is no greater
// than {M1}.
// An "exclusive" assertion concerns two methods or subtypes, and
// declares that there are at most two (or perhaps later N>2)
// specific items that jointly satisfy the restriction.
// We list all items explicitly rather than just giving their
// count, for robustness in the face of complex schema changes.
// A context class CX (which may be either abstract or concrete)
// has two exclusive concrete subtypes* C1, C2 if every concrete
// subtype* of CX is either C1 or C2. Note that if neither C1 or C2
// are equal to CX, then CX itself must be abstract. But it is
// also possible (for example) that C1 is CX (a concrete class)
// and C2 is a proper subtype of C1.
// This dependency asserts that MM(CX, M1) is no greater than {M1,M2}.
// This dependency asserts that no instances of class or it's
// subclasses require finalization registration.
// This dependency asserts when the CallSite.target value changed.
};
enum {
// handy categorizations of dependency types:
// A "context type" is a class or interface that
// provides context for evaluating a dependency.
// When present, it is one of the arguments (dep_context_arg).
//
// If a dependency does not have a context type, there is a
// default context, depending on the type of the dependency.
// This bit signals that a default context has been compressed away.
};
static bool has_explicit_context_arg(DepType dept) { return dept_in_mask(dept, explicit_ctxk_types); }
static bool has_implicit_context_arg(DepType dept) { return dept_in_mask(dept, implicit_ctxk_types); }
static int dep_implicit_context_arg(DepType dept) { return has_implicit_context_arg(dept) ? 0 : -1; }
private:
// State for writing a new set of dependencies:
}
int x_id = x->ident();
// return true if we've already seen dept/x
}
void sort_all_deps();
// Initialize _deps, etc.
// State for making a new set of dependencies:
// Logging support
public:
// Make a new empty dependencies set.
}
private:
// Check for a valid context type.
// Enforce the restriction against array types.
}
}
}
public:
// Adding assertions to a new dependency set at compile time:
void assert_evol_method(ciMethod* m);
// Define whether a given method or type is concrete.
// These methods define the term "concrete" as used in this module.
// For this module, an "abstract" class is one which is non-concrete.
//
// Future optimizations may allow some classes to remain
// non-concrete until their first instantiation, and allow some
// methods to remain non-concrete until their first invocation.
// In that case, there would be a middle ground between concrete
// and abstract (as defined by the Java language and VM).
// These versions of the concreteness queries work through the CI.
// The CI versions are allowed to skew sometimes from the VM
// (oop-based) versions. The cost of such a difference is a
// (safely) aborted compilation, or a deoptimization, or a missed
// optimization opportunity.
//
// In order to prevent spurious assertions, query results must
// remain stable within any single ciEnv instance. (I.e., they must
// not go back into the VM to get their value; they must cache the
// bit in the CI, either eagerly or lazily.)
static bool has_finalizable_subclass(ciInstanceKlass* k);
// As a general rule, it is OK to compile under the assumption that
// a given type or method is concrete, even if it at some future
// point becomes abstract. So dependency checking is one-sided, in
// that it permits supposedly concrete classes or methods to turn up
// as really abstract. (This shouldn't happen, except during class
// evolution, but that's the logic of the checking.) However, if a
// supposedly abstract class or method suddenly becomes concrete, a
// dependency on it must fail.
// Checking old assertions at run-time (in the VM only):
static klassOop check_abstract_with_exclusive_concrete_subtypes(klassOop ctxk, klassOop k1, klassOop k2,
static klassOop check_call_site_target_value(oop call_site, oop method_handle, CallSiteDepChange* changes = NULL);
// A returned klassOop is NULL if the dependency assertion is still
// valid. A non-NULL klassOop is a 'witness' to the assertion
// failure, a point in the class hierarchy where the assertion has
// been proven false. For example, if check_leaf_type returns
// non-NULL, the value is a subtype of the supposed leaf type. This
// witness value may be useful for logging the dependency failure.
// Note that, when a dependency fails, there may be several possible
// witnesses to the failure. The value returned from the check_foo
// method is chosen arbitrarily.
// The 'changes' value, if non-null, requests a limited spot-check
// near the indicated recent changes in the class hierarchy.
// It is used by DepStream::spot_check_dependency_at.
// Detecting possible new assertions:
// Create the encoding which will be stored in an nmethod.
void encode_content_bytes();
return _content_bytes;
}
return _size_in_bytes;
}
void log_all_dependencies();
}
}
private:
// helper for encoding common context types as zero:
public:
// Use this to iterate over an nmethod's dependency set.
// Works on new and old dependency sets.
// Usage:
//
// ;
// Dependencies::DepType dept;
// for (Dependencies::DepStream deps(nm); deps.next(); ) {
// ...
// }
//
// The caller must be in the VM, since oops are not wrapped in handles.
class DepStream {
private:
#ifdef ASSERT
#endif
// iteration variables:
inline oop recorded_oop_at(int i);
// => _code? _code->oop_at(i): *_deps->_oop_recorder->handle_at(i)
public:
{
}
{
}
bool next();
return _xi[i]; }
return (methodOop) x;
}
return (klassOop) x;
}
// The point of the whole exercise: Is this dep still OK?
return check_call_site_dependency(NULL);
}
// A lighter version: Checks only around recent changes in a class
// hierarchy. (See Universe::flush_dependents_on.)
// Log the current dependency to xtty or compilation log.
// Print the current dependency to tty.
};
friend class Dependencies::DepStream;
};
// Every particular DepChange is a sub-class of this class.
public:
// What kind of DepChange is this?
virtual bool is_klass_change() const { return false; }
virtual bool is_call_site_change() const { return false; }
// Subclass casting with assertions.
return (KlassDepChange*) this;
}
return (CallSiteDepChange*) this;
}
void print();
public:
enum ChangeType {
};
// Usage:
// for (DepChange::ContextStream str(changes); str.next(); ) {
// klassOop k = str.klass();
// switch (str.change_type()) {
// ...
// }
// }
private:
friend class DepChange;
// iteration variables:
int _ti_index;
int _ti_limit;
// start at the beginning:
void start();
public:
{ start(); }
// the nsv argument makes it safe to hold oops like _klass
{ start(); }
bool next();
};
friend class DepChange::ContextStream;
};
// A class hierarchy change coming through the VM (under the Compile_lock).
// The change is structured as a single new type with any number of supers
// and implemented interface types. Other than the new type, any of the
// super types can be context types for a relevant dependency, which the
// new type could invalidate.
private:
// each change set is rooted in exactly one new type (at present):
void initialize();
public:
// notes the new type, marks it and all its super-types
{
initialize();
}
// cleans up the marks
~KlassDepChange();
// What kind of DepChange is this?
virtual bool is_klass_change() const { return true; }
// involves_context(k) is true if k is new_type or any of the super types
bool involves_context(klassOop k);
};
// A CallSite has changed its target.
private:
public:
: _call_site(call_site),
{
}
// What kind of DepChange is this?
virtual bool is_call_site_change() const { return true; }
};
#endif // SHARE_VM_CODE_DEPENDENCIES_HPP