Patent Application
20130124836
1. Field of the Invention
The current disclosure relates to a constant data accessing system and, in particular, to a constant data accessing system managing a value of constant pool base address in a constant pool base register.
2. Description of the Related Art
MIPS32 uses a conventional constant accessing method that constructs a 32-bit constant by two 32-bit instructions, Load Upper Immediate (LUI) and Or Immediate (ORI). In
Another one related art is program-counter-relative data access. X86-64, ARM, and DEC VAX support this instruction type. When program-counter-relative data access is used, compiler places the constants in a constant pool before or after the subroutine that uses the constants. And then, use program-counter-relative instructions to access the constants.
In the assembly code, the data at address 0x100 is the initialized value zero of the global variable “global_var”. The address of the global variable “global_var” is a constant data put at address 0x00c. The address of the global variable “global_var” is loaded by the program-counter-relative load instruction at address 0x000. Therefore, the code size of accessing the constant data is 6-bytes.
However, when the code size of the subroutine is very large, the address distance from the program-counter-relative load instruction to the address of the constant also becomes longer. In this case, the instruction size of the program-counter-relative load instruction is 4 bytes. Therefore, in this case, the code size of accessing the constant data is 8-bytes.
In order to improve the conventional constant accessing, there is a need for a constant data accessing system and method thereof.
The present invention discloses a constant data accessing system that comprises a compiler having a constant pool handler; an instruction set is module having a constant pool base register management instruction set unit and a constant pool access instruction set unit; and a computer processor having a constant pool base register. The constant pool base register is configured to store a value of constant pool base address of one or a plurality of subroutines which have constants to be accessed. The constant pool handler is configured to manage and access the constants in one or a plurality of subroutines.
The present invention discloses a computer processor supporting an instruction set module that comprises a constant pool base register is configured to store a value of a constant pool base address of one or a plurality of subroutines having constants being accessed. The instruction set module has a constant pool base register management instruction set unit and a constant pool access instruction set unit.
The present invention discloses a method of constant data accessing of one or a plurality of subroutines that comprises the steps of placing one or a plurality of constants in a constant pool; determining a value of constant pool base address; managing the value in a constant pool base register; and accessing the one or the plurality of constants with involving the constant pool base register. The step of managing the value in a constant pool base register comprises setting, saving, and restoring the value in the constant pool base register.
In order to have further understanding of the techniques, means, and effects of the current disclosure, the following detailed description and drawings are hereby presented, such that the purposes, features and aspects of the current disclosure may be thoroughly and concretely appreciated; however, the drawings are provided solely for reference and illustration, without any intention to be used for limiting the current disclosure.
The objectives and advantages of the present invention are illustrated is with the following description and upon reference to the accompanying drawings in which:
The present invention discloses a constant data accessing system.
In the system 20, the main function of the compiler 21 is to compile a source code 22 to a machine code 24 which is executable by the computer processor 23. The compiler 21 uses the instruction set module 25 to compile the source code 22.
In the compiler 21, the main function of the constant pool handler 27 is to manage and access the constants in one or a plurality of subroutines.
In Step S501, one or a plurality of constants is placed in a constant pool.
In Step S503, a value of constant pool base address is determined.
The constant pool base register 26 is configured to store a value of constant pool base address of one or a plurality of subroutines which have constants to be accessed. When the program flow enters to a new subroutine upon subroutine call or subroutine return, the content of constant pool base register 26 should be managed by instructions in constant pool base register management instruction set unit 28; shown in Step S505. The constant pool base register management comprises saving caller's constant pool base register before setting callee's constant pool base register by Push-CPBR instruction either in caller or in callee; setting the callee's constant pool base register before the first constant access of the callee by Call-and-Set-CPBR instruction upon subroutine call in caller or by Set-CPBR instruction in callee; restoring the caller's constant pool base register after a last constant access of the callee and before a next constant access of the caller by Pop-CPBR instruction in callee, or by Pop-CPBR-and-return instruction upon return in callee, or by Pop-CPBR in caller.
Moreover, for further code size reduction purpose, saving caller's constant pool base register before setting callee's constant pool base register by Push-CPBR instruction in caller, and setting the callee's constant pool base register before the first constant access of the callee by Call-and-Set-CPBR instruction upon subroutine call in caller can be performed with a single instruction by Push-CPBR-and-Call-and-Set-CPBR in caller. Saving caller's constant pool base register before setting callee's constant pool base register by Push-CPBR instruction in callee, and setting the callee's constant pool base register before the first constant access of the callee by Set-CPBR instruction in callee can be performed with a single instruction by Push-CPBR-and-Set-CPBR in callee.
The following figures are combinations of constant pool base register manager in the caller's subroutine body and in the callee's subroutine body.
Although the present invention and its objectives have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, many of the processes discussed above can be implemented using different methodologies, replaced by other processes, or a combination thereof.
Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
