JP2000029716A - Register allocating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten compilation times by decreasing the number of variables to be allocated by substituting variable which are defined at the same time with another certain variable, regarding the substitutive variable as an object of register allocation. SOLUTION: In a compiler 10, a register allocation part 203 inputs an intermediate code 40 for the generation of a variable information table and generates the variable information table for storing reference point information, etc., on respective variables. To replace variable which are defined at a definition points at the same time with another certain variable, a substitution table is generated. When registers are searched, the variable information table allocates the registers to the generated variables, while checking the reference point information, etc. When a reference point is converted, a variable table substitute the reference by a register for reference by a variable to which the register is allocated for the generated variable. For a variable to which no register is allocated, the reference by the variable is replaced with reference from a memory.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compiler register allocating method.

[0002]

2. Description of the Related Art In a compiler for converting a source program into a target code, many optimization methods for improving the execution performance of the target code have been developed so far. V. Eiho, R.A. Cessy, J.M. D. This is described in detail in Ullman's "Compiler".

[0003] One of the optimization methods is to reduce the number of references to a memory for a variable referred to in a source program, and execute the program with data loaded in a register which is a limited resource. As a process for improving the execution time of the target code, there is a process called register allocation.

As a method of register allocation, Ch
aitin, G .; J. "Register All
location and Spilling via
Graph Coloring ": Proc. of
ACM SIGGPLAN '82 Compiler
Construction, 98-105 (198
The paper 2) describes a register allocation method. In the method of this paper, when there are n variables to be assigned, the compilation time is required by n ² .

[0005]

FIG. 10 shows the above-mentioned prior art.
The processing procedure in the register allocating unit when compiling the source program shown in FIG. 1 will be described with reference to FIGS. 12, 13, and 14. In the register allocation process, first, a variable information table of variables appearing in the source program is created, and then a register to be allocated to the variable for which the variable information table has been generated is searched. In the generation process of the variable information table, a sentence is extracted from the intermediate code (step 1201), and it is checked whether or not the sentence exists (step 1202). If a statement exists, it is checked whether a variable information table of a variable appearing as a reference point in the statement has been generated. If the variable information table has not been generated, a variable information table for the variable is generated at this point (step 1203). In FIG. 10, since four variables (a, b, c, d) appear, FIG.
The four variable information tables are generated as shown in FIG. Next, register search processing is performed, which is repeated by the number of variable information tables generated in the processing of FIG. 12 (steps 1301 and 1302). This register search process generally takes longer than the time to create a variable information table or the like.

[0006] The problem of the prior art is that when a plurality of statements in which a plurality of variables are defined at a time appear as shown in FIG. 10, the number of variables to be allocated to registers increases and the compilation time increases. It is to be.

[0007] It is an object of the present invention to reduce the compile time by replacing the definitions of a plurality of variables with one other variable and reducing the number of variables to be assigned.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the number of variables by replacing the definition of a plurality of variables with the definition of another variable and assigning only the replaced variables to registers. This can be achieved by:

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a register allocating method in a compiler.

An embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited by this.

FIG. 1 is a system configuration diagram of an embodiment of a register allocating method according to the present invention.

This system comprises a CPU device 1, a memory device 2, an input device 3, and a display device 4. The compiler 10 is processed and executed by the CPU device 1. The compiler 10 inputs the source program 30 and generates the intermediate code 40 several times, and finally generates the target code 50. The purpose code 50 is executed in the execution 20 and displays the result on the display device 4 or outputs the result to the execution result 60.

FIG. 2 is a processing configuration diagram in the compiler 10.

The compiler 10 includes an intermediate code generator 20
1. An intermediate code optimization generation unit 202, a register allocation unit 203, and a target code generation unit 204. In the intermediate code generation unit 201, the source program 30 is input,
After performing lexical analysis and syntax analysis, an intermediate code 40 is generated. The intermediate code optimization generation unit 202 outputs the intermediate code 40
And after performing some optimizations, the intermediate code 40
Generate The register allocating unit 203 receives the intermediate code 40 and generates the intermediate code 40 in which each variable is referred to as a register or a memory. The target code generation unit 204 receives the intermediate code 40 and generates a target code 50 to be executed by each machine.

FIG. 7 shows a table structure of the variable information table 700.

This table includes a replacement flag field 701 indicating whether a variable is replaced, a pointer field 702 indicating a replacement table for associating a replaced variable with a variable before replacement, and reference point information. It comprises a pointer field 703 indicating a table, an assigned register number field 704 for storing a register number assigned to a variable, and a pointer field 705 indicating the next variable information table.

FIG. 8 shows a table structure of the reference point table 800.

This table includes a pointer field 801 indicating an intermediate code, a reference point attribute field 802 for storing the attribute of the reference point, and a pointer field 803 indicating the next reference point table.

FIG. 9 shows a table structure of the replacement table 900.

This table includes a field 901 indicating a set of variables before replacement, a pointer field 902 indicating a variable information table of variables after replacement, and an allocation indicating conditions of registers to be assigned to variables before replacement, if any. It consists of a condition field 903 and a pointer field 904 indicating the next replacement table.

FIG. 3 shows an example of the processing of the register allocating section 203.

In generating a variable information table in step 301, the intermediate code 40 is input, and a variable information table for storing reference point information of each variable is generated. In addition, a substitution table is generated to replace a plurality of variables simultaneously defined at the definition point with one different variable.

In the search for the registers in step 302, registers are allocated to the variables for which the variable information table has been generated, while checking reference point information and the like.

In the conversion of the reference point in step 303, the variable in which the register is assigned to the variable for which the variable information table has been generated replaces the variable reference with the register reference. For a variable to which no register is assigned, the reference in the variable is replaced with the reference from the memory.

FIG. 4 shows an example of the processing of the generation 301 of the variable information table.

In the generation of the variable information table, a sentence is extracted from the intermediate code 40 (step 401), and it is checked whether or not there is a sentence (step 402). In step 410, when a plurality of variables are simultaneously defined at the definition point of the sentence, the definition point is replaced with one other variable, the replacement information is registered in the replacement table 700, and the reference information of the definition point is registered. Is the definition of the variable after substitution. Then, the condition for allocating the register to the variable before replacement is set in the allocation condition field 903 of the replacement table.

Next, it is checked whether or not a variable information table of the variable referred to by the use point and the definition point of the statement has been generated. If not, a variable information table of the variable is generated (step 403). ).

If the registered variable is a variable after replacement in step 410, the replacement flag field 701 of the variable information table is marked to determine whether the registered variable is a normal variable or a variable that has been replaced. A distinction is made (step 411).

Finally, the reference point information of the use point and the definition point is
It is registered in the reference point table field 703 of each variable information table (step 404).

FIG. 5 shows an example of the register search process 302.

In the register search processing, one variable information is taken out from the variable information table (step 501), and it is checked whether the variable information exists (step 502).
If the variable information table exists, it is checked whether the variable is a replaced variable (step 503).
Whether a variable has been replaced can be determined by examining the replacement flag field 703 of the variable information table.

If it is not a substitution variable, a search is made for a register to be assigned to the variable (step 503). If there is a register to be assigned, the register number is assigned to the assigned register number field 7 of the variable information table.
Register in 04.

In the case of a substitution variable, the assignment condition field 903 of the substitution table is examined, and if a condition is set, a register to be assigned according to the condition is searched. If the condition is not set, a search is made for registers to be allocated by the number of variables before replacement (step 51).
1).

FIG. 6 shows an example of the reference point conversion processing 303.

The reference point conversion process is a process of converting each reference point into a reference in a register based on the register information assigned to each variable.

First, in the reference point conversion process, one variable information is extracted from the variable information table (step 60).
1) Check whether variable information exists (step 602). If the variable information exists, one reference point of the variable is extracted (step 603), and it is checked whether or not the reference point exists (step 604). If there is a reference point, it is checked whether the reference point is a definition point in which a plurality of variables are simultaneously defined, that is, a reference point to be replaced (step 605). In the case of the reference point to be replaced, it is checked whether a register is allocated to the replacement variable (step 606).

If a register has been assigned, it is checked whether the assigned register satisfies the condition set in the assignment condition field of the replacement table (step 607). If the condition is satisfied, the original reference point is converted into a reference in the allocated register (step 608). If a register satisfying the condition is not allocated in step 607, a reserve register satisfying the condition is taken out, and the original reference point is converted into a reference of the reserve register (step 609).

If the reference point is a use point, a copy instruction from the allocated register to the reserved register is generated and inserted as a statement immediately before the original reference point. If the reference point is a definition point, a copy instruction from the reserved register to the allocated register is generated and inserted as a statement immediately after the original reference point (step 610). If no register is allocated in step 606, a reserved register satisfying the condition is taken out, and the original reference point is converted into a reference of the reserved register (step 615).

If the reference point is a use point, a load instruction from the memory to the reserve register is generated and inserted as a statement immediately before the original reference point. If the reference point is a definition point, a store instruction from the reserved register to the memory is generated and inserted as a statement immediately after the original reference point (step 616).
If it is determined in step 605 that the reference point has not been replaced, a normal reference point conversion process is performed. It is checked whether or not a register is allocated (step 611). If the register is allocated, the original reference point is converted into a reference of the allocated register (step 612).

If no register is assigned in step 611, the reserved register is taken out and the original reference point is converted into a reference in the reserved register (step 61).
3). If the reference point is a use point, a load instruction from the memory to the reserved register is generated and inserted as a statement immediately before the original reference point. If the original reference point is a definition point, a store instruction from the reserved register to the memory is generated and inserted as a statement immediately after the original reference point (step 614).

FIG. 11 shows the variable information table 700 and the replacement table 9 when the source program of FIG.
FIG. 5 is a conceptual diagram showing a connection state of a reference point table 800 and an intermediate code 40.

The procedure from the reading of the source program of FIG. 10 to the creation of the diagram of FIG. 11 will be described. First, since the source program processes from the point of use, first, a variable information table of the variable c is created.
Since the variable c is not a substitution variable, the substitution flag is 'FALSE'
Is set to Then, a reference table for indicating the use point is created, and this table is pointed to from the variable information table. The pointer field to the intermediate code of the reference point table is an intermediate code 40
Will point to the sentence inside. Various tables of the variable d are similarly created.

The definition point is replaced by another variable because a plurality of variables are defined. Replace the variable name after replacement
If it is set to 1, first, a variable information table of replace1 is created. Then, a substitution table is created to associate the variable (a, b) before substitution with the variable replace1 after substitution. The pre-replacement variables (a, b) are set in the set fields of the pre-replacement variables in the substitution table, and rep is stored in the pointer field to the variable information table of the post-replacement variables.
The variable information table of the place1 is set. Also, r
The replacement table is pointed out from the variable information table of replace1. The relationship between the variable before replacement and the variable after replacement can be associated with each other by the connection state of these tables.

FIG. 15 shows an example of the result when the conventional register allocation method is applied to the source program of FIG. Here, it is assumed that continuous registers need to be allocated to the variables a and b. In the conventional allocation method,
Since the condition for allocating consecutive registers to the variable a and the variable b is not considered, the possibility of allocating consecutive registers is reduced. For example, when consecutive registers are not allocated, the original reference point indicated by 1500 is converted into a reference in the reserved register (step 609), and 15
A copy instruction from the reserved register indicated by 10, 1520 to the allocated register is required (step 61).
0).

FIG. 16 shows an example of the result when the variables a and b in the source program of FIG. 10 are replaced with the variable replace1, and the registers are allocated. Substitution variable r
When searching for a register to be assigned to eplace1,
Since a continuous register that satisfies the condition is searched for (step 511), the definition points of the original variables a and b are converted into references in the allocated registers (step 60).
8) The possibility of doing it increases. For this reason, in the conventional method, a copy instruction from the reserved register to the allocated register was required.However, in this method, the possibility of generating a copy instruction is reduced, and the execution time is reduced by the amount of time that the copy instruction is not executed. Will be improved.

In this example, it is assumed that reg1 and reg2 are consecutive registers.

[0047]

According to the present invention, the number of variables to be allocated can be reduced by replacing a plurality of variables defined at the same time with one other variable and making the replaced variables the registers to be allocated. Compile time can be reduced.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of register allocation according to an embodiment of the present invention.

FIG. 2 is a processing configuration diagram of a compiler of FIG. 1;

FIG. 3 is a flowchart illustrating a procedure of register allocation processing.

FIG. 4 is a flowchart illustrating a procedure of generating a variable information table.

FIG. 5 is a flowchart showing a register search processing procedure.

FIG. 6 is a flowchart illustrating a reference point conversion processing procedure.

FIG. 7 is a configuration diagram of a variable information table.

FIG. 8 is a configuration diagram of a reference point table.

FIG. 9 is a configuration diagram of a replacement table.

FIG. 10 is a diagram showing an example of a source program.

FIG. 11 is a conceptual diagram showing a connection state between various tables and an intermediate code.

FIG. 12 is a flowchart illustrating a conventional variable information table generation processing procedure.

FIG. 13 is a flowchart showing a conventional register search processing procedure.

FIG. 14 is a conceptual diagram showing a connection state of various tables and intermediate codes according to a conventional procedure.

FIG. 15 is a diagram showing a register allocation result (1).

FIG. 16 is a diagram showing a register allocation result (No. 2).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CPU apparatus, 2 ... memory apparatus, 3 ... input apparatus, 4 ...
Display device, 10 ... Compiler.

Claims (2)

[Claims] In a statement in which a plurality of variables are defined by a certain operation, compile time is reduced by a process of replacing the definitions of a plurality of variables with a definition of another variable and a process of allocating registers to the replaced variables. Register allocation method. 2. A process according to claim 1, wherein when replacing the definition of a plurality of variables with the definition of another variable, a process for registering a condition for allocating registers to the original plurality of variables, and allocating registers according to the conditions. A register allocating method characterized by allocating registers according to conditions to a plurality of variables by processing.