Accelerated class check
Reaching a determination associated with a class of an object is disclosed. An identifier associated with the class of the object is extracted from a pointer to the object. The extracted identifier is compared to a comparison value. At least in part using a result of the comparison a determination is reached.
1. A method for reaching a determination associated with a class of an object, comprising:
extracting, from a pointer to the object, an identifier associated with the class of the object;
comparing the extracted identifier to a dynamically determined comparison value, wherein the comparison value is a predicted object class identifier for the object; and
reaching a determination associated with the class of the object at least in part using a result of the comparison;
wherein reaching the determination includes:
determining that the extracted identifier does not match the comparison value during the comparison;
using the extracted identifier to locate a table entry in a table that includes a plurality of table entries mapping a plurality of class identifiers to a corresponding plurality of class data;
using the located table entry to locate a virtual method table;
identifying an address associated with a code section; and
jumping to the identified address.
2. A method as recited in claim 1 , wherein the pointer to the object is associated with a first group of one or more bits included in an instruction.
3. A method as recited in claim 2 , wherein the comparison value is associated with a second group of one or more bits included in the instruction.
4. A method as recited in claim 1 , wherein reaching the determination includes performing a trap when the extracted identifier does not match the comparison value.
5. A method as recited in claim 1 , wherein extracting the class identifier includes extracting from the pointer one or more bits that are not implemented as address bits.
6. A method as recited in claim 1 , wherein reaching the determination is at least a portion of preparing, handling, or executing an invocation associated with a method of the object.
7. A method as recited in claim 6 , wherein preparing the invocation includes modifying data associated with a stack frame.
8. A method as recited in claim 6 , wherein the invocation includes a virtual method invocation.
9. A method as recited in claim 1 , wherein the comparison value is associated with a virtual method invocation of the predicted object class.
10. A method as recited in claim 1 , wherein the comparison value is associated with a previous virtual call.
11. A method as recited in claim 1 , wherein when the extracted identifier matches the comparison value during the comparison, reaching the determination includes jumping to a comparison address of a program code section.
12. A method as recited in claim 1 , wherein when the extracted identifier does not match the comparison value during the comparison, reaching the determination includes obtaining a class structure pointer associated with the object.
13. A method as recited in claim 1 , wherein the object is not loaded.
14. A method as recited in claim 1 , wherein the identifier consists of a less number of bits than a number of bits used to represent a class structure associated with the object.
15. A method as recited in claim 1 , wherein the identifier consists of a less number of bits than a total number of bits not implemented as address bits in the pointer to the object.
16. A method as recited in claim 1 , further comprising validating the identifier as a valid identifier.
17. A computer program product comprising instruction at least in part used to reach a determination associated with a class of an object, the computer program product comprising instruction being embodied in a computer readable storage medium, the instruction comprising:
a first set of one or more bits identifying the instruction;
a second set of one or more bits associated with a pointer to the object, wherein the pointer includes an identifier associated with the class of the object; and
a third set of one or more bits associated with a dynamically determined comparison value used in a comparison with the identifier, wherein the comparison value is a predicted object class identifier for the object;
wherein in the event that the identifier associated with the class of the object does not match the comparison value:
the identifier is used to locate a table entry in a table that includes a plurality of table entries mapping a plurality of class identifiers to a corresponding plurality of class data;
the located table entry is used to locate a virtual method table, identify an address associated with a code section, and direct a processor to jump to the identified address.
18. The computer program product comprising instruction as recited in claim 17 , wherein the second set and the third set includes one or more of the following: an immediate value to be directly used in the comparison, memory address associated with a value to be used in the comparison, and an identifier of a register containing a value to be used in the comparison.
19. The computer program product comprising instruction as recited in claim 17 , wherein the instruction includes a group of one or more bits specifying one or more of the following: an instruction format specification, a format of an instruction field, and a configuration associated with an operation of the instruction.
20. The computer program product comprising instruction as recited in claim 17 , wherein the first set of one or more bits is at least in part used to determine one or more operations associated with the instruction.
21. The computer program product comprising instruction as recited in claim 17 , wherein when the extracted identifier does not match the comparison value during the comparison, a trap is performed.
22. The computer program product comprising instruction as recited in claim 17 , wherein the comparison is associated with preparing, handling, or executing an invocation associated with a method of the object.
23. A system for reaching a determination associated with a class of an object, comprising:
a processor configured to:
extract, from a pointer to the object, an identifier associated with the class of the object;
compare the extracted identifier to a dynamically determined comparison value, wherein the comparison value is a predicted object class identifier for the object; and
reach a determination associated with the class of the object at least in part using a result of the comparison;
wherein reaching the determination includes:
determining that the extracted identifier does not match the comparison value during the comparison;
using the extracted identifier to locate a table entry in a table that includes a plurality of table entries mapping a plurality of class identifiers to a corresponding plurality of class data;
using the located table entry to locate a virtual method table;
identifying an address associated with a code section; and
jumping to the identified address; and
a memory coupled to the processor.
24. A system as recited in claim 23 , wherein the pointer to the object is associated with a first group of one or more bits included in an instruction used by the processor.
25. A system as recited in claim 24 , wherein the comparison value is associated with a second group of one or more bits included in the instruction used by the processor.
26. A system as recited in claim 23 , wherein the processor is further configured to perform a trap when the extracted identifier does not match the comparison value.
27. A system as recited in claim 23 , wherein the determination associated with the class of an object is at least a portion of preparing, handling, or executing an invocation associated with a method of the object.