Method and apparatus for resolving data references in generated code

Abstract

A hybrid compiler-interpreter comprising a compiler for "compiing" source program code, and an interpreter for interpreting the "compiled" code, is provided to a computer system. The compiler comprises a code generator that generates code in intermediate form with data references made on a symbolic basis. The interpreter comprises a main interpretation routine, and two data reference handling routines, a dynamic field reference routine for handling symbolic references, and a static field reference routine for handling numeric references. The dynamic field reference routine, when invoked, resolves a symbolic reference and rewrites the symbolic reference into a numeric reference. After rewriting, the dynamic field reference routine returns to the main interpretation routine without advancing program execution to the next instruction thereby allowing the rewritten instruction with numeric reference to be reexecuted. The static field reference routine, when invoked, obtain data for the program from a data object based on the numeric reference. After obtaining data, the static field reference routine advances program execution to the next instruction before returning to the interpretation routine. The main interpretation routine selectively invokes the two data reference handling routines depending on whether the data reference in an inspection is a symbolic or a numeric reference.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of computer systems, in particular, programming language compilers and interpreters of these computer systems. More specifically, the present invention relates to resolving references in compiler generated object code.

2. Background

The implementation of modern programming languages, including object oriented programming languages, are generally grouped into two categories: compiled and interpreted.

In a compiled programming language, a computer program (called a compiler) compiles the source program and generates executable code for a specific computer architecture. References to data in the generated code are resolved prior to execution based on the layout of the data objects that the program deals with, thereby, allowing the executable code to reference data by their locations. For example, consider a program that deals with a point data object containing two variables x and y, representing the x and y coordinates of a point, and further assume that the variables x and y are assigned slots 1 and 2 respectively, in each instance of the point data object. Thus, an instruction that accesses or fetches, y, such as the Load instruction 14 illustrated in FIG. FIG. 1 shows FIGS. 1A & 1B show the prior art compiled approach and the prior art interpreted approach to resolving data reference.

FIG. 2 illustrates an exemplary computer system incorporated with the teachings of the present invention.

FIG. 3 illustrates the software elements of the exemplary computer system of FIG. 2.

FIG. 4 illustrates one embodiment of the compiler of the hybrid compiler-interpreter of the present invention.

FIG. 5 illustrates one embodiment of the code generator of the compiler of FIG. 4.

FIG. 6 illustrates one embodiment of the interpreter and operator implementations of the hybrid compiler-interpreter of the present invention.

FIG. 7 illustrates the cooperative operation flows of the main interpretation routine, the static field reference routine and the dynamic field reference routine of the present invention.

FIG. 8 illustrates an exemplary resolution and rewriting of a data reference under the present invention.

DETAILED DESCRIPTION PRESENTLY PREFERRED AND ALTERNATE EMBODIMENTS

A method and apparatus for generating executable code and resolving data references in the generated code is disclosed. The method and apparatus provides execution performance substantially similar to the traditional compiled approach, as well as the flexibility of altering data objects like the traditional interpreted approach. The method and apparatus has particular application to implementing object oriented programming languages. In the following description for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without the specific details. In other instances, well known systems are shown in diagrammatical or block diagram form in order not to obscure the present invention unnecessarily.

Referring now to FIGS. 2 and 3, two block diagrams illustrating an exemplary computer system incorporated with the teachings of the present invention are shown. As shown in FIG. 2, the exemplary computer system 20 comprises a central processing unit (CPU) 22, a memory 24, and an I/O module 26. Additionally, the exemplary computer system 20 also comprises a number of input/output devices 30 and a number of storage devices 28. The CPU 22 is coupled to the memory 24 and the I/O module 26. The input/output devices 30, and the storage devices 28 are also coupled to the I/O module 26. The I/O module 26 in turn is coupled to a network 32.

Except for the manner they are used to practice the present invention, the CPU 22, the memory 24, the I/O module 26, the input/output devices 30, and the storage devices 28, are intended to represent a broad category of these hardware elements found in most computer systems. The constitutions and basic functions of these elements are well known and will not be further described here.

As shown in FIG. 3, the software elements of the exemplary computer system of FIG. 2 comprises an operating system 36, a hybrid compiler-interpreter 38 incorporated with the teachings of the present invention, and applications compiled and interpreted using the hybrid compiler-interpreter 38. The operating system 36 and the applications 40 are intended to represent a broad categories of these software elements found in many computer systems. The constitutions and basic functions of these elements are also well known and will not be described further. The hybrid compiler-interpreter 38 will be described in further detail below with references to the remaining figures.

Referring now to FIGS. 4 and 5, two block diagrams illustrating the compiler of the hybrid compiler-interpreter of the present invention are shown. Shown in FIG. 4 is one embodiment of the compiler 42 comprising a lexical analyzer and parser 44, an intermediate representation builder 46, a semantic analyzer 48, and a code generator 50. These elements are sequentially coupled to each other. Together, they transform program source code 52 into tokenized statements 54, intermediate representations 56, annotated intermediate representations 58, and ultimately intermediate form code 60 with data references made on a symbolic basis. The lexical analyzer and parser 44, the intermediate representation builder 46, and the semantic analyzer 48, are intended to represent a broad category of these elements found in most compilers. The constitutions and basic functions of these elements are well known and will not be otherwise described further here. Similarly, a variety of well known tokens, intermediate representations, annotations, and intermediate forms may also be used to practice the present invention.

As shown in FIG. 5, the code generator 50 comprises a main code generation routine 62, a number of complimentary operator specific code generation routines for handling the various operators, such as the ADD and the IF code generation routines, 64 and 66, and a data reference handling routine 68. Except for the fact that generated coded 60 are in intermediate form and the data references in the generated code are made on a symbolic basis, the main code generation routine 62, the operator specific code generation routines e.g. 64 and 66, and the data reference handling routine 68, are intended to represent a broad category of these elements found in most compilers. The constitutions and basic functions of these elements are well known and will not be otherwise described further here.

For further descriptions on various parsers, intermediate representation builders, semantic analyzers, and code generators, see A. V. Aho, R. Sethi, and J. D. Ullman, Compilers Principles, Techniques and Tools, Addison-Wesley, 1986, pp. 25-388, and 463-512.

Referring now to FIGS. 6 and 7, two block diagrams illustrating one embodiment of the interpreter of the hybrid compiler-interpreter of the present invention and its operation flow for handling data references is shown. As shown in FIG. 6, the interpreter 70 comprises a main interpretation routine 72, a number of complimentary operator specific interpretation routines, such as the ADD and the IF interpretation routines, 74 and 76, and two data reference interpretation routines, a static field reference routine (SFR) and a dynamic field reference routine (DFR), 78 and 80. The main interpreter routine 72 receives the byte codes 82 of the intermediate form object code as inputs, and interprets them, invoking the operator specific interpretation routines, e.g. 74 and 76, and the data reference routines, 78 and 80, as necessary. Except for the dynamic field reference routine 80, and the manner in which the main interpretation routine 72 and the state field reference routine 78 cooperates with the dynamic field reference routine 80 to handle data references, the main interpretation routine 72, the operator specific interpretation routines, e.g. 74 and 76, and the static field reference routine 78, are intended to represent a broad category of these elements found in most compilers and interpreters. The constitutions and basic functions of these elements are well known and will not be otherwise described further here.

As shown in FIG. 7, upon receiving a data reference byte code, block 86, the main interpretation routine determines if the data reference is static, i.e. numeric, or dynamic, i.e. symbolic, block 88. If the data reference is a symbolic reference, branch 88b, the main interpretation routine invokes the dynamic field reference routine, block 90. Upon invocation, the dynamic field reference routine resolves the symbolic reference, and rewrites the symbolic reference in the intermediate form object code as a numeric reference, block 92. Upon rewriting the data reference in the object code, the dynamic field reference routine returns to the main interpretation routine, block 100, without advancing the program counter. As a result, the instruction with the rewritten numeric data reference gets reexecuted again.

On the other hand, if the data reference is determined to be a numeric reference, branch 88a, the main interpretation routine invokes the static field reference routine, block 94. Upon invocation, the static field reference routine obtain the data referenced by the numeric reference, block 96. Upon obtaining the data, the static field reference routine advances the program counter, block 98, and returns to the main interpretation routine, block 100.

Referring now to FIG. 8, a block diagram illustrating the alteration and rewriting of data references under the present invention in further detail is shown. As illustrated, a data referencing instruction, such as the LOAD instruction 14", is initially generated with a symbolic reference, eg. "y". Upon its first interpretation in execution, the data referencing instruction, e.g. 14, is dynamically resolved and rewritten with a numeric reference, e.g. slot 2. Thus, except for the first execution, the extra level of interpretation to resolve the symbolic reference is no longer necessary. Therefore, under the present invention, the "compiled" intermediate form object code of a program achieves execution performance substantially similar to that of the traditional compiled object code, and yet it has the flexibility of not having to be recompiled when the data objects it deals with are altered like that of the traditional translated code, since data reference resolution is performed at the first execution of a generated instruction comprising a symbolic reference.

While the present invention has been described in terms of presently preferred and alternate embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described. The method and apparatus of the present invention can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting on the present invention.

Claims

1. In a computer system comprising a program in source code form, a method for generating executable code for said program and resolving data references in said generated code, said method comprising the steps of:

a) generating executable code in intermediate form for said program in source code form with data references being made in said generated code on a symbolic basis, said generated code comprising a plurality of instructions of said computer system;

b) interpreting said instructions, one at a time, in accordance to a program execution control;

c) resolving said symbolic references to corresponding numeric references, replacing said symbolic references with their corresponding numeric references, and continuing interpretation without advancing program execution, as said symbolic references are encountered while said instructions are being interpreted; and

d) obtaining data in accordance to said numeric references, and continuing interpretation after advancing program execution, as said numeric references are encountered while said instruction are being interpreted;

said steps b) through d) being performed iteratively and interleavingly.

2. The method as set forth in claim 1, wherein, said program in source code form is implemented in source code form of an object oriented programming language.

3. The method as set forth in claim 2, wherein, said programming language is C.

4. The method as set forth in claim 2, wherein, said programming language is C++.

5. The method as set forth in claim 1, wherein,

said program execution control is a program counter;

said continuing interpretation in step c) is achieved by performing said step b) after said step c) without incrementing said program counter; and

said continuing interpretation in said step d) is achieved by performing said step b) after said d) after incrementing said program counter.

6. In a computer system comprising a program in source code form, an apparatus for generating executable code for said program and resolving data references in said generated code, said apparatus comprising:

a) compilation means for receiving said program in source code form and generating executable code in intermediate form for said program in source code form with data references being made in said generated code on a symbolic basis, said generated code comprising a plurality of instructions of said computer system;

b) interpretation means for receiving said generated code and interpreting said instructions, one at a time;

c) dynamic reference handling means coupled to said interpretation means for resolving said symbolic references to corresponding numeric references, replacing said symbolic references with their corresponding numeric references, and continuing interpretation by said interpretation means without advancing program execution, as said symbolic references are encountered while said instructions are being interpreted by said interpretation means; and

d) static reference handling means coupled to said interpretation means for obtaining data in accordance to said numeric references, and continuing interpretation by said interpretation means after advancing program execution, as said numeric references are encountered while said instruction are being interpreted by said interpretation means;

said interpretation means, said dynamic reference handling means, and said static reference handling means performing their corresponding functions iteratively and interleavingly.

7. The apparatus as set forth in claim 6, wherein, said program in source code form is implemented in source code form of an object oriented programming language.

8. The apparatus as set forth in claim 7, wherein, said programming language is C.

9. The apparatus as set forth in claim 7, wherein sad programming language is C++.

10. The apparatus as set forth in claim 6, wherein, said program execution control is a program counter.

11. A method for interpreting software in intermediate form code, said intermediate form code comprising instructions, certain of said instructions containing one or more symbolic references, said method comprising the steps of:

interpreting said instructions in accordance with a program execution control;

operative when an instruction being interpreted contains an unresolved symbolic reference, resolving said unresolved symbolic reference, said step of resolving said unresolved symbolic reference including substeps of:

determining a numerical value corresponding to said unresolved symbolic reference, and

storing said numerical value in a memory; and

operative when an instruction being interpreted contains a resolved symbolic reference, interpreting said instruction by reading said stored numerical value. 12. The method of claim 11, where said substep of storing said numerical value comprises the substep of storing said numerical value in said instruction containing an unresolved symbolic reference. 13. The method of claim 12, where said substep of storing said numerical value in said instruction comprises the substep of replacing said unresolved symbolic reference with said numerical value.

14. The method of claim 12, where said step of resolving said unresolved symbolic reference further comprises the substep of interpreting said instruction containing an unresolved symbolic reference following said substep of storing said numerical value in said instruction containing a symbolic reference. 15. The method of claim 14, where said step of resolving said unresolved symbolic reference further comprises the substep of advancing said program execution control only after said substep of interpreting said instruction containing an unresolved symbolic reference. 16. The method of claim 11, where said unresolved symbolic reference is a data reference. 17. The method of claim 11, where said unresolved symbolic reference is a reference to a field in a data object. 18. The method of claim 11, where the source code of said software comprises code written in a non-object-oriented programming language. 19. The method of claim 11, where the source code of said software comprises code written in an object-oriented programming

language. 20. The method of claim 11, where said program execution control comprises a program counter. 21. The method of claim 11, where said instruction containing an unresolved symbolic reference comprises one or more machine instructions of said computer. 22. A method for compiling software into intermediate form code, said method comprising the steps of:

lexically analyzing source code of said software,

parsing output of said lexical analysis step,

building an intermediate representation from said parsed output, and

generating intermediate form code containing symbolic field references from said intermediate representation. 23. The method of claim 22, where said symbolic field references comprise data references. 24. The method of claim 23, where said data references comprise references to fields within data objects. 25. In a computer, an apparatus for interpreting software in intermediate form code, said intermediate form code comprising instructions, certain of said instructions containing one or more symbolic references, said apparatus comprising:

a first device configured to interpret said instructions in accordance with a program execution control;

a second device configured, operative when an instruction being interpreted contains an unresolved symbolic reference, to resolve said unresolved symbolic reference, said second device comprising:

a third device configured to determine a numerical value corresponding to said unresolved symbolic reference, and

a fourth device configured to store said numerical value in a memory; and

a fifth device configured, operative when an instruction being interpreted contains a resolved symbolic reference, to interpret said instruction by

reading said stored numerical value. 26. An apparatus for compiling software into intermediate form code, said apparatus comprising:

a first device configured to lexically analyze the source code of said software,

a second device configured to parse output of said first device,

a third device configured to build an intermediate representation from said parsed output, and

a fourth device configured to generate intermediate form code containing symbolic field references from said intermediate representation. 27. A computer system, comprising a plurality of one or more interconnected computers, at least one of said plurality of computers comprising an apparatus for interpreting software in an intermediate form code, said intermediate form code comprising instructions, certain of said instructions containing one or more symbolic references, said apparatus comprising:

a first device configured to interpret said instructions in accordance with a program execution control;

a second device configured, operative when an instruction being interpreted contains an unresolved symbolic reference, to resolve said unresolved symbolic reference, said second device comprising:

a third device configured to determine a numerical value corresponding to said unresolved symbolic reference, and

a fourth device configured to store said numerical value in a memory of said at least one of said plurality of computers; and

a fifth device configured, operative when an instruction being interpreted contains a resolved symbolic reference, to interpret said instruction by reading said stored numerical value. 28. A computer system, comprising a plurality of one or more interconnected computers, at least one of said plurality of computers comprising an apparatus for compiling software into intermediate form code, said apparatus comprising:

a first device configured to lexically analyze the source code of said software,

a second device configured to parse the output of said device configured to lexically analyze,

a third device configured to build an intermediate representation from said parsed output, and

a fourth device configured to generate intermediate form code containing symbolic field references from said intermediate representation.

29. A computer program product comprising:

a computer readable medium having computer readable code embodied therein for interpreting software in an intermediate form code, said intermediate form code comprising instructions, certain of said instructions containing one or more symbolic references, said computer readable medium comprising:

a computer readable program code device configured to interpret said instructions in accordance with a program execution control;

a second computer readable program code device configured, operative when an instruction being interpreted contains an unresolved symbolic reference, to resolve said unresolved symbolic reference, said second computer readable program code device comprising:

a third computer readable program code device configured to determine a numerical value corresponding to said unresolved symbolic reference, and

fourth computer readable program code device configured to store said numerical value in a memory of said at least one of said plurality of computers; and

a fifth computer readable program code device configured, operative when an instruction being interpreted contains a resolved symbolic reference, to interpret said instruction by reading said stored numerical value.

30. A computer program product comprising:

a computer readable medium having computer readable code embodied therein for compiling software into intermediate form code, said computer readable medium comprising:

a first computer readable program code device configured to lexically analyze source code of said software,

a second computer readable program code device configured to parse the output of said first computer readable program code device,

a third computer readable program code device configured to build an intermediate representation of said parsed output, and

a fourth computer readable program code device configured to generate intermediate form code containing symbolic field references from said intermediate representation. 31. A system for distributing code stored on a computer readable medium, said code comprising computer readable code for interpreting software in an intermediate form code, said intermediate form code comprising instructions, certain of said instructions containing one or more symbolic references, said computer readable medium comprising:

a computer readable program code device configured to interpret said instructions in accordance with a program execution control;

a second computer readable program code device configured, operative when an instruction being interpreted contains an unresolved symbolic reference, to resolve said unresolved symbolic reference, said second computer readable program code device comprising:

a third computer readable program code device configured to determine a numerical value corresponding to said unresolved symbolic reference, and

a fourth computer readable program code device configured to store said numerical value in a memory of said at least one of said plurality of computers; and

a fifth computer readable program code device configured, operative when an instruction being interpreted contains a resolved symbolic reference, to interpret said instruction by reading said stored numerical value. 32. A system for distributing code stored on a computer readable medium, said code comprising computer readable code for compiling software into intermediate form code, said computer readable medium comprising:

a first computer readable program code device configured to lexically analyze source code of said software,

a second computer readable program code device configured to parse the output of said first computer readable program code device,

a third computer readable program code device configured to build an intermediate representation of said parsed output, and

a fourth computer readable program code device configured to generate intermediate form code containing symbolic field references from said

intermediate representation. 33. A method for distributing code stored on a computer readable medium, said code comprising computer readable code for interpreting software in an intermediate form code, said intermediate form code comprising instructions, certain of said instructions containing one or more symbolic references, said computer readable medium comprising:

a computer readable program code device configured to interpret said instructions in accordance with a program execution control;

a second computer readable program code device configured, operative when an instruction being interpreted contains an unresolved symbolic reference, to resolve said unresolved symbolic reference, said second computer readable program code device comprising:

a third computer readable program code device configured to determine a numerical value corresponding to said unresolved symbolic reference, and

a fourth computer readable program code device configured to store said numerical value in a memory of said at least one of said plurality of computers; and

a fifth computer readable program code device configured, operative when an instruction being interpreted contains a resolved symbolic reference, to interpret said instruction by reading said stored numerical value,

said method comprising the steps of reading a portion said computer readable code from said computer readable medium into a memory and writing said portion of said code to a second computer readable medium.

34. A method for distributing code stored on a computer readable medium, said code comprising computer readable code for compiling software into intermediate form code, said computer readable medium comprising:

a first computer readable program code device configured to lexically analyze source code of said software,

a second computer readable program code device configured to parse the output of said first computer readable program code device,

a third computer readable program code device configured to build an intermediate representation of said parsed output, and

a fourth computer readable program code device configured to generate intermediate form code containing symbolic field references from said intermediate representation,

said method comprising the steps of reading a portion of said computer readable code from said computer readable medium into a memory and writing said portion of said code to a second computer readable medium.

35. A computer implemented method for interpreting intermediate form code comprised of instructions, certain of said instructions containing one or more symbolic references, said method comprising the steps of:

interpreting said instructions in accordance with a program execution control; and

resolving a symbolic reference in an instruction being interpreted, said step of resolving said symbolic reference including the substeps of:

determining a numerical reference corresponding to said symbolic reference,

and storing said numerical reference in a memory. 36. The method of claim 35, wherein said substep of storing said numerical reference comprises the substep of replacing said symbolic reference with said numerical reference. 37. The method of claim 35, wherein said step of resolving said symbolic reference further comprises the substep of interpreting said instruction containing said symbolic reference using the stored numerical reference. 38. The method of claim 37, wherein said step of resolving said symbolic reference further comprises the substep of advancing said program execution control after said substep of interpreting said instruction containing said symbolic reference.