JP3313859B2 - Redundant remover - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a redundant expression removing apparatus provided in a compiler for translating a source program written in a high-level language into a machine language program, for removing redundant arithmetic expressions from a program to be processed. .

[0002]

2. Description of the Related Art In recent years, it has been actively practiced to write programs in a high-level language such as the C language to increase the efficiency of program development. The source programs described in these high-level languages are translated into machine language programs that can be understood by a computer by using various compilers.

The compiler is designed to shorten the execution time of the machine language program finally created and reduce the memory size (the execution time of the machine language program finally created or the cost of the memory size is reduced collectively). Various processes are performed on a source program created by a programmer or an intermediate language program created by a compiler to perform internal processing. One of the methods for reducing costs in this way is to delete redundant arithmetic expressions from a program. In order to delete such a redundant operation expression (this operation expression is referred to as a redundant expression), a conventional compiler is provided with a redundant expression removing device for removing the redundant expression by various deletion methods. Before describing the redundant elimination device, the terms used are defined below. Operation This refers to a program code composed of variables, constants, and operators, for example, 100 * x + 2, x / 200 + y. Operational expressions For example, y = 130, y = 100 * x + 2, y = x / 2
An expression with variables on the left side of the equal sign and operations on the right side, such as 00 + 10. Definition of Variables To set the contents of variables by calculation, for example, a = b + c and s = 100 * 2. -Use of variables The use of variables as operands in operations. -Stack variables These are variables placed on the memory in the stack area. -Static variables These are variables that are stored in the memory at a specific address outside the stack area.・ Register variables Variables placed on registers. First, a redundant-type elimination device that deletes a common sub-expression will be described. Deletion of a common subexpression refers to a process of, when there are a plurality of operations performing exactly the same operation in a program, deleting all but one of them except for one of them. FIG. 10 is a configuration diagram of a redundant-type removing device that deletes a common sub-expression.

A redundant expression elimination device for deleting a common sub-expression (a device for deleting a common sub-expression in the figure) includes an operation appearance location detection unit 22, a result usage location detection unit 23, and an operand rewriting unit. 24, an arithmetic expression removing unit 25, and a processing target holding unit 26. The operation appearance location detection unit 22 detects all operations having exactly the same operand from the program stored in the processing target storage unit 26. In particular,
The operation appearance location detection unit 22 compares the operators and operands of all the operations in the program stored in the processing target storage unit 26 (when the operand is a variable, the contents of the variable are compared). This is used for comparison.), And the operands detect all the same operations. After the detection, the calculation appearance location detection unit 22 notifies the calculation expression removal unit 25 of the position of the calculation expression whose calculation exists on the right side of the equal sign (this calculation expression is referred to as a common subexpression). In addition, variables defined by the detected operation are detected, and among these variables, the variable located at the first position (this variable is referred to as a designated variable) is read by the operand rewriting unit 24.
, And the variables located at the second and subsequent positions (these variables are called deletion variables) are output to the result use location detection unit 23.

[0005] The result use location detection unit 23 receives the deletion variable from the calculation appearance location detection unit 22 and
An operation that is used as an operand (this operation is called a rewrite operation expression) is detected, and the detected position is notified to the operand rewrite unit 24. The operand rewriting unit 24 receives the specified variable from the operation appearance location detecting unit 22 and specifies the deleted variable used as the operand in the rewriting operation expression of the position notified from the result usage location detecting unit 23. Rewrite to a variable.

The operation expression removing unit 25 deletes the operation expression at the position notified from the operation appearance location detection unit 22. The processing target holding unit 26 holds a program to be processed.
The retained program may be described by a source code described by a programmer, or may be described by an internal code generated by a compiler for the sake of internal processing.

[0007] The redundant-type elimination apparatus configured to remove the common sub-expression deletes the common sub-expression from the program shown in FIG. First, the operation appearance location detection unit 22 detects the operation indicated by the arrows a1, a2, and a3. Next, the result use location detection unit 23 detects an operation (operation indicated by arrows b1 and b2 in the figure) in which x1 and y1 that are deletion variables are used as operands. After detection,
The operand rewriting unit 24 converts the operands of the operations of the arrows b1 and b2 into the designated variable x as indicated by the arrows c1 and c2 in FIG.
Rewrite to As a result, this program is rewritten as shown in FIG.

[0008] Second, a description will be given of a redundant type removing apparatus for transmitting a value. Value propagation means that in an operation, a variable used as an operand is replaced with a variable or constant having the same value, and the operation expression of the variable used as the operand is deleted from the program. It is to be. FIG. 13 is a configuration diagram of a redundant-type removing device that propagates a value.

The redundant expression elimination device that propagates the value (the device that propagates the value in the figure) includes a substitution occurrence location detection unit 32, a result use location detection unit 33, an operand rewriting unit 34,
It is composed of an assignment removing unit 35 and a processing target holding unit 36. The substitution occurrence location detection unit 32 detects all the arithmetic expressions for substituting variables into constants or the arithmetic expressions for substituting variables into variables from the program stored in the processing target storage unit 36, and determines the position of the arithmetic expression. , To the substitution removing unit 35.
Further, it detects a variable defined by the detected arithmetic expression (this variable is also referred to as a deleted variable) and outputs it to the operand rewrite unit 34. In the above equation, variables and constants existing on the right side of the equal sign (these are called designated substitution numbers)
Is output to the operand rewriting unit 34.

The result use location detection unit 33 receives the deletion variable from the substitution appearance location detection unit 32, and performs an operation in which the deletion variable is used as an operand (this operation is called a rewrite operation expression). The detected position is notified to the operand rewriting unit 34. The operand rewrite unit 34 receives the designated number of substitutions from the substitution appearance location detection unit 32, and replaces the deletion variable used as the operand in the rewrite operation expression at the position notified from the result use location detection unit 33 with: Rewrite with the specified number of substitutions.

The substitution removing unit 35 includes the result use place detecting unit 3.
3 deletes the arithmetic expression at the position notified. The processing target holding unit 36 holds a program to be processed, like the processing target holding unit 26. The redundant expression removing device configured to propagate a value configured as described above propagates a value to a program as shown in FIG. First, the substitution appearance location detection unit 32 detects the operation formula indicated by the arrow d1, and then the result use location detection unit 33 detects the operation indicated by the arrow e1, e2. After the detection, the operand rewriting unit 24 outputs an arrow e
The operands of the operations of e1 and e2 are represented by arrows f1 and f2 in FIG.
Is rewritten to the designated substitution number 4000. as a result,
This program is rewritten as shown in FIG.

[0012]

However, according to the above-mentioned prior art, a redundant expression elimination device for deleting a common sub-expression and propagating a value requires an operand of an operation to be processed,
Since the operand was rewritten without checking whether it was a constant, a register variable, a stack variable, or a static variable, there was a problem that the rewriting would actually increase the cost. Was.

Further, the processor of the target machine is
If an addressing mode such as an indirect address reference with an index and an offset and an indirect address reference with an offset can be used, the compiler cannot rewrite an operation that can effectively utilize these addressing modes. There was a problem that the cost was not sufficiently reduced.

For example, in the programs shown in FIGS. 11 and 14, a variable x is a stack variable placed in a stack area, and variables x1 and y1 are register variables placed on registers. In general, stack variables require access to the memory in the stack area and are more expensive than register variables. Therefore, if the operation using the register variables x1 and y1 is rewritten to the stack variable x,
Rewriting can increase the cost of the entire program. In a machine language instruction, an operation using a constant value of 16 bits or more as an operand requires that the operand be described in the operand of the machine language instruction.
In many cases, the cost is higher than an operation using a memory as an operand. Therefore, when the variable x in FIG. 7 is rewritten to a constant value of 16 bits or more, the rewriting may increase the cost of the entire program.

FIG. 16A shows a part of a program in which address calculation is described using pointer variables in C language, and FIG. 16B shows a result of resource allocation of these variables. is there. Although the processor of the target machine is a two-operand type processor, FIG.
Address register indirect reference as shown in FIG. As described above, even in a situation where the addressing mode can be used, the rewriting performed by the compiler is a rewriting for a two-operand type processor.
The operation cannot be rewritten to correspond to the machine language instruction in the addressing mode (c). Therefore, the compiler cannot use such a machine language instruction for performing indirect address register reference in the process of translating the machine language program, and the cost of the program increases accordingly.

In view of the above problems, the present invention determines whether rewriting is valid before rewriting an operand of an operation, and rewrites the operand if rewriting is valid. It is an object of the present invention to provide a redundant expression elimination device that eliminates an arithmetic expression that becomes unnecessary by rewriting and rewrites an operation so that the addressing mode is effectively used.

[0017]

In order to solve the above-mentioned problems, a redundant expression elimination apparatus according to the present invention is provided in a compiler,
A redundant expression eliminator for rewriting an operation of a program held in a program holding unit and removing a redundant operation expression after the rewriting, wherein a same operation is performed by the program of the program holding unit using the same operator and operand. Detect all, detect all variables defined by the operation,
An operation detecting means for storing the position of the operation expression including the detected operation and the variable, and the second and subsequent variables among the variables detected by the operation detecting means detect all the operations used as operands Operand detecting means, a type of an arithmetic expression, and cost storage means for storing the cost of the arithmetic expression corresponding to the type of the arithmetic expression, and a type of the arithmetic expression detected by the operand detecting means. The first cost extracting means for retrieving the cost corresponding to the type of the operation expression by searching the cost storage means, and the variable detected by the operation detecting means in the operand of the arithmetic expression detected by the operand detecting means. Out of the cost storage means by the type of the arithmetic expression in the case of using the variable located at the first position, and extracting the cost corresponding to the type of the arithmetic expression.
The cost taking means, the cost means taken out by the first cost taking means, and the cost means taken out by the second cost taking means, and the comparing means make a comparison. If the cost is small,
In the operation detected by the operand detection means, the rewriting means for rewriting the position of the variable used as the operand in the program with the variable detected first by the operation detection means, and the operand detection means If the rewriting means rewrites all the variables in the operation, the operation expression including the variable used as the operand in the operation detected by the operand detection means and the operation in which the variable was defined To
Removing means for removing from the program.

Further, the first cost extracting means obtains the sum of the extracted costs, the second cost extracting means obtains the total of the extracted costs, and the comparing means obtains the total of the extracted costs. The total cost may be compared with the total cost obtained by the second cost extracting means. Also,
The comparing means may compare the individual costs extracted by the first cost extracting means with the individual costs extracted by the second cost extracting means.

[0019]

[0020]

[0021] Also, provided to the compiler, it rewrites the operation of the program held in the program holding means, after rewriting, a redundant type removing apparatus for removing redundant operation expression is held in the program holding means An arithmetic expression that substitutes a constant for a variable, an arithmetic expression detection unit that detects all the arithmetic expressions that assign the value of a variable to a variable, and the left side of the equal sign of the arithmetic expression detected by the arithmetic expression detection unit The variables present in the operands detect the operands used as operands from the program holding means, and the types of the operands and the operands of the operands corresponding to these types. A cost storage unit that stores the cost and a cost storage unit that is searched by the type of the arithmetic expression detected by the operand detection unit, and fetches a cost corresponding to the type of the arithmetic expression.
And cost storage in the form of an arithmetic expression when the first variable of the variables detected by the arithmetic expression detection means is used as the operand of the arithmetic expression detected by the operand detection means. The second cost extracting means for retrieving the means and extracting the cost corresponding to the type of the arithmetic expression, the cost extracted by the first cost extracting means, and the cost extracted by the second cost extracting means are compared. The comparison unit compares the cost extracted by the first cost extraction unit with the cost detected by the second cost extraction unit, and the comparison unit compares the cost detected by the second cost extraction unit. If the cost is small, the rewriting means for rewriting the position in the program of the variable used as the operand in the operation detected by the operand detection means to the variable or constant detected by the arithmetic expression detection means And the case where the variable in all operations were detected operands detecting means, rewriting rewriting means,
The variable used as the operand in the operation detected by the operand detection means is an arithmetic expression present on the left side of the equal sign,
And a removing unit for removing, from the program, the arithmetic expression detected by the arithmetic expression detecting unit.

Further, the first cost taking means finds the sum of the taken out costs, the second cost taking out means finds the total of the taken out costs, and the comparing means finds the sum of the taken out costs. The total sum of the costs obtained and the total sum of the costs obtained by the second cost extracting means may be compared. The comparing means may compare the individual costs extracted by the first cost extracting means with the individual costs extracted by the second cost extracting means.

[0023]

[0024] Also, provided to the compiler, it rewrites the operation of the program held in the program holding means, after rewriting, a redundant type removing apparatus for removing redundant arithmetic expression, the program in the program holding means An operation detecting means for detecting an operation expression in which a variable which is a pointer is defined, and storing the position of the operation expression including the detected operation and the variable, and using the variable detected by the operation detection means as an operand. Operand detection means for detecting all of the operation expressions being performed, an operation expression that can be executed by one machine language instruction, and is used for a pointer, an operand used for an index, And a type for storing the type of the operand including at least two of the operands used for the offset and the cost of the operation expression corresponding to the type of the operation expression. A first cost extracting means for searching the cost storage means with the arithmetic expression detected by the operand detection means and extracting the cost of the arithmetic expression corresponding to the arithmetic expression; A second cost extraction for retrieving the cost storage means and retrieving the cost corresponding to the arithmetic expression in the form of the arithmetic expression when the operation detected by the arithmetic detection means is applied to the operand of the detected arithmetic expression. Means, the cost taken out by the first cost taking out means, and the second cost taking out means.
The comparison means for comparing the cost extracted by the cost extraction means with the cost extraction means, and as a result of the comparison, if the cost extracted by the second cost extraction means is small, the operation expression The rewriting means rewrites the position in the program of the variable used as the operator to the operation detected by the operation detection means, and the rewriting means rewrites the variables in all the arithmetic expressions detected by the operand detection means. In this case, a removing means is provided for removing, from the program, an arithmetic expression including the arithmetic operation detected by the arithmetic detecting unit.

Further, the first cost taking means finds the sum of the taken out costs, the second cost taking out means finds the total of the taken out costs, and the comparing means finds the sum of the taken out costs. The total sum of the costs obtained and the total sum of the costs obtained by the second cost extracting means may be compared. The comparing means may compare the individual costs extracted by the first cost extracting means with the individual costs extracted by the second cost extracting means.

[0026]

[0027]

[0028]

[0029]

According to the above-mentioned means, in the redundant expression elimination apparatus of the present invention, the operation detecting means operates on the program of the program holding means, and all the operations having the same operator and operand are detected. All the defined variables are detected, and the positions of the arithmetic expressions including the detected operations and the variables are stored. The operand detection means operates on the variables located after the second among the variables detected by the operation detection means, and all the operations used as the operands are detected. The cost storage means stores the types of the arithmetic expressions and the costs of the arithmetic expressions corresponding to the types of the arithmetic expressions, and the cost storage means A search is performed based on the type of the arithmetic expression detected by the child detecting means, and the cost corresponding to the type of the arithmetic expression is extracted. In the cost storage means, the second cost extraction means uses the first variable among the variables detected by the operation detection means as the operand of the arithmetic expression detected by the operand detection means. The search is performed using the type of the arithmetic expression in the case, and the cost corresponding to the type of the arithmetic expression is extracted. After the taking out, the cost taken out by the first cost taking out means and the cost taken out by the second cost taking out means are compared by the comparing means. As a result of the comparison by the comparing means, if the cost extracted by the second cost extracting means is small, the position in the program of the variable used as the operand in the operation detected by the operand detecting means is replaced by the rewriting means. Thus, the variable is rewritten to the first variable detected by the operation detecting means. When the rewriting means rewrites all variables in the operation detected by the operand detection means, the variable used as the operand in the operation detected by the operand detection means and the variable are defined. And an operation expression including the calculated operation are removed from the program by the removal means.

[0030]

[0031]

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A redundant type removing apparatus according to an embodiment of the present invention will be described. This redundant-type eliminator, like C language,
Provided in a high-level language compiler that can describe address calculation using variables, the compiler performs lexical analysis, syntax analysis, and semantic analysis of the source program, and the contents of each variable are each operation in the program. Fired after parsing how many values are in the expression. The program to be processed is an intermediate language program that is output as an analysis result after the compiler performs lexical analysis, syntax analysis, and semantic analysis. FIG. 1 shows the configuration of this redundant type removing device.

The redundant expression elimination device 10 includes a control unit 1, an operation generation position detection unit 3, a value use position detection unit 4, a cost storage unit 5, an addressing cost storage unit 6, a cost extraction unit 7,
A first rewriting cost extracting section 8, a second rewriting cost extracting section 9, a third rewriting cost extracting section 10, a comparing section 1
1, a first rewriting unit 12, a first arithmetic expression removing unit 13,
The second rewriting unit 14, the second arithmetic expression removing unit 15, the third
, A third arithmetic expression removing unit 17, and a processing target holding unit 18.

The control unit 1 includes a calculation generation position detecting unit 3, a value use position detecting unit 4, a cost extracting unit 7, a first rewriting cost extracting unit 8, a second rewriting cost extracting unit 9, and a third rewriting cost. The extraction unit 10 and the comparison unit 11 are activated in order.
The calculation generation position detection unit 3 includes a calculation appearance position detection unit 3a,
Substitution occurrence position detection unit 3b and pointer operation expression detection unit 3c
Consists of

The operation appearance position detecting section 3a detects all the operations having exactly the same operand from the program stored in the processing target storing section 21. Specifically, the operation appearance position detection unit 3a compares the operators and operands of all the operations in the program stored in the processing target storage unit 18 (when the operand is a variable, The contents of the variable are used for comparison.), And all the same operations are detected. After the detection, the calculation appearance position detection unit 3a calculates the first calculation formula (this calculation formula is referred to as a designated calculation formula) among the calculation formulas whose calculation is on the right side of the equal sign, and extracts the cost. 7 is output. Next, the positions of the second and subsequent arithmetic expressions are notified to the first arithmetic expression removing unit 13 (this arithmetic expression is called a common sub-expression). In addition, it detects variables defined by the detected arithmetic expression, and outputs a variable located at the first position (this variable is referred to as a designated variable) to the first rewriting cost extracting unit 8. The variable located after the second (this variable is called a deleted variable) is output to the first value use position detection unit 4a.

The substitution appearance position detection unit 3b detects all the arithmetic expressions for substituting constants for variables or the arithmetic expressions for substituting variable values for variables from the program stored in the processing target storage unit 18, The position of the detected arithmetic expression is notified to the second arithmetic expression removing unit 15. Further, a variable substituted by the detected arithmetic expression (this variable is also referred to as a deleted variable in this embodiment) is detected and sent to the second value use position detecting unit 4b and the second rewriting cost extracting unit 9. Output. Further, in the above arithmetic expression, the variable and the constant (these are also referred to as designated substitution numbers) existing on the right side of the equal sign are output to the second rewriting cost extracting unit 9.

The pointer arithmetic expression detection unit 3c detects all the arithmetic expressions defining the pointer variables from the program stored in the processing target storage unit 21. Specifically, the pointer arithmetic expression detection unit 3c detects all the arithmetic expressions in which the pointer variable exists on the left side of the equal sign, among the arithmetic expressions in the program held in the processing target holding unit 18. After the detection, the pointer operation expression detecting unit 3c outputs the detected pointer variable to the third value use position detecting unit 4c, and performs an operation for defining the pointer variable (this operation is called a pointer operation, the pointer operation and the pointer variable Is referred to as a pointer operation expression.), And is output to the third rewrite cost extracting unit 10. Finally, the position of the arithmetic expression detected is notified to the third arithmetic expression removing unit 17.

The value using position detecting section 4 comprises a first value using position detecting section 4a, a second value using position detecting section 4b, and a third value using position detecting section 4c. The first value use position detection unit 4a receives the deletion variable from the operation appearance position detection unit 3a, and uses an operation expression in which the deletion variable is used as an operand (in this embodiment, this operation is rewritten by an operation Expressions) are all detected. After the detection, the first value use position detecting unit 4a determines whether a variable used as an operand in the arithmetic expression is defined in a region from the common subexpression to the rewrite arithmetic expression in the program. Check if it is not defined, and rewrite the first
Is output to the rewriting cost extracting unit 8.

The second value use position detection unit 4b receives the deletion variable from the substitution appearance position detection unit 3b, and
It detects all the arithmetic expressions used as operands (this operation is also called a rewrite arithmetic expression in this embodiment) and outputs it to the second rewrite cost extracting unit 9. The third value use position detecting unit 4c receives the pointer variable from the pointer arithmetic expression detecting unit 3c, and calculates the arithmetic expression in which the pointer variable is used as the operand (in this embodiment, this arithmetic operation is also rewritten. This is called an arithmetic expression.)
Are all detected. After the detection, the third value use position detector 4c
Checks whether the variable used as the operand in the operation is defined in the area from the pointer variable to the rewrite operation expression in the program, and if it is not defined, Is output to the third rewriting cost extracting unit 10.

The cost storage unit 5 stores the type of an arithmetic expression and the cost of the arithmetic expression corresponding to the type of the arithmetic expression. In the present embodiment, there are five items for which the types of the above arithmetic expressions are determined, and these items are search items for the cost extracting unit 7 and the first rewriting cost extracting unit 8 to perform a search. The cost storage unit 5 stores costs corresponding to combinations of these search items. FIG. 2 shows that the target machine is a two-operand system and the second to f
This shows an example of what is called the first method (method in which the second operand acts on the first operand). The above-mentioned search items include an item of an operator type, an item of an operation type, an item of an operand (referred to as a first operand) on the right side of the operator, and an operand on the left side of the operator ( And a storage location for the operation result. The items of the above-described types of operators indicate types of operators, such as addition, subtraction, multiplication, and division. The operation type item is an 8-bit integer type,
The operation types such as 16-bit integer type, 32-bit integer type, single-precision floating-point type, and double-precision floating-point type are shown. In the first and second types of operands, the operand stores constants, static variables, static variables storing pointers, stack variables, stack variables storing pointers, register variables, and pointers. Variable types, such as register variables, are shown.
The item of the storage location of the operation result indicates a variable type such as a static variable, a static variable for storing a pointer, a stack variable, a stack variable for storing a pointer, a register variable, a register variable for storing a pointer, and the like. I have. In the item of cost, the number of clocks of the machine language instruction or the memory size corresponding to the conditions of these search items is recorded.
In FIG. 2, the variable storing the pointer is described as a pointer in the lower item.

The addressing cost storage unit 6 stores the cost of a machine language instruction using an addressing mode for the third rewriting cost extracting unit 10 to perform a search. FIG. 3 shows an example of the addressing cost storage unit 6. The configuration of the addressing cost storage unit 6 is similar to the cost storage unit 5. The difference is that the addressing cost storage unit 6 has an item of the second operator and an item of the operand (third operand) existing on the right side of the second operator. The cost corresponding to the combination of the two search items is stored.

The cost fetching unit 7 includes the calculation appearance position detecting unit 3
The cost storage unit 5 is searched with the designated arithmetic expression detected by a, and the cost of the machine language instruction corresponding to the arithmetic expression is extracted and output to the comparison unit 11. Specifically, the cost extracting unit 7
The designated operation expression is received from the operation appearance position detection unit 3a, the type of the variable used as the operand in the received designated operation expression is checked, and it is determined whether the first and second operands are constants. Whether it is a static variable, a static variable that stores a pointer, a stack variable, a stack variable that stores a pointer, a register variable, or a register variable that stores a pointer . After examining these, the cost extracting unit 7 determines whether the storage location of the operation result is a static variable, a static variable storing a pointer, a stack variable, or a stack variable storing a pointer. Check whether it is a register variable, or a register variable that stores a pointer. Based on the results of these investigations, the cost storage unit 5 is searched, and the corresponding costs are extracted and output to the comparison unit 11.

The first rewriting cost extracting unit 8 receives the designated variable from the operation appearance position detecting unit 3a, receives the rewriting operation expression from the first value use position detecting unit 4a, and deletes the deletion variable in the rewriting operation expression. Then, the cost storage unit 5 is searched with the rewritten arithmetic expression, and the cost of the arithmetic expression is extracted and output to the comparison unit 11. For example, the variable a is a designated variable, the variable b is a deletion variable, and the operation expression “d =
If “b + 3” is a rewrite operation expression, the first rewrite cost extraction unit 8 searches the cost storage unit 5 by rewriting the operation expression “d = b + 3” to the operation expression “d = a + 3”,
The cost is extracted and output to the comparison unit 11. The method of searching for the cost performed by the first rewriting cost fetching unit 8 is the same as that of the cost fetching unit 7, and therefore the description is omitted.

The second rewrite cost extracting unit 9 receives the deletion variable and the designated number of substitutions from the substitution appearance position detection unit 3b, receives the rewrite operation expression from the second value use position detection unit 4b, and determines whether the deletion variable is It is determined whether or not the pointer is stored. If the pointer is stored, the deleted variable in the rewrite operation expression is rewritten to the designated substitution number, and the cost storage unit 5 is searched and rewritten by the rewritten operation expression. The cost corresponding to the operation expression is extracted and output to the comparison unit 11. For example, when the variable 3 is the designated substitution number, the variable b is a deletion variable, and the operation expression “a = b + c” is a rewrite operation expression, the first
The rewriting cost extraction unit 8 of the formula “a = b + c”
The cost is rewritten to the operation “a = 3 + c”, the cost storage unit 5 is searched, and the cost is extracted and output to the comparison unit 11. Second
The method of retrieving the cost performed by the rewriting cost extracting section 9 is the same as that of the cost extracting section 7, and thus the description is omitted.

The third rewriting cost extracting unit 10 receives the pointer variable and the pointer operation from the pointer operation expression detecting unit 3c, receives the rewriting operation expression from the third value use position detecting unit 4c, and Delete variable
The operation is rewritten as a pointer operation, the addressing cost storage unit 6 is searched by the rewritten operation, the cost of the machine language instruction in the addressing mode corresponding to the operation is extracted and output to the comparison unit 11. For example, the variable b is the designated substitution number, the designated operation is “a + 2”, and the rewrite operation expression is “d = b
+ C ”, the first rewriting cost extracting unit 8
The rewrite operation expression “d = b + c” is converted into the operation “d = a + 2 +
The addressing cost storage unit 6 is searched by rewriting to “c”, and the cost is extracted and output to the comparison unit 11. The cost retrieval method is the same as that of the cost extracting unit 7.

The comparing unit 11 receives the costs extracted by the cost extracting unit 7, the first cost rewriting extracting unit 8, the second cost rewriting extracting unit 9, and the third cost rewriting extracting unit 10, and compares the costs. Do. Upon receiving the costs from the cost extracting unit 7 and the first cost rewriting extracting unit 8, the comparing unit 11 compares them. As a result of the comparison, if the cost extracted by the first rewriting cost extracting unit 8 is small, the first rewriting unit 12 is activated. Similarly, if the costs are received from the second cost rewriting and extracting unit 9 and the third rewriting cost extracting unit 10, the comparing unit 11
These are compared with the costs received from the cost retrieving unit 7, and if the costs retrieved by the second rewriting cost retrieving unit 9 and the third rewriting cost retrieving unit 10 are small, the second rewriting unit 14, the third rewriting cost Is started up.

The first rewriting unit 12 receives the designated variable from the operation appearance position detection unit 3a, and specifies the program position of the deletion variable in the rewrite operation expression detected by the first value use position detection unit 4a. Rewrite to a variable. When the first rewriting unit 12 rewrites all the deleted variables to the designated variables, the first operation expression removing unit 13
The arithmetic expression at the position notified from a is deleted from the program.

The second rewriting unit 14 receives the deletion variable from the substitution appearance position detection unit 3b, and specifies the program position of the deletion variable in the rewrite operation expression detected by the second value use position detection unit 4b. Rewrite with the number of substitutions. When the second rewriting unit 14 rewrites all the deletion variables to the designated variables, the second calculation expression removal unit 15 deletes the calculation expression at the position notified from the substitution appearance position detection unit 3b from the program.

The third rewriting unit 16 receives the pointer operation from the operation appearance position detection unit 3a, and determines the program position of the pointer variable in the rewrite operation expression detected by the third value use position detection unit 4c by the pointer. Rewrite the operation. The third arithmetic expression removing unit 17 includes a third rewriting unit 16
Rewrites all the delete variables to the designated variables, the pointer arithmetic expression at the position notified from the pointer arithmetic expression detection unit 3c is deleted from the program.

The processing target holding unit 18 holds a program to be processed. The retained program is described by an internal code generated by the compiler for internal processing. The held program may be described by a source code described by a programmer.
The operation of the redundant-type removing device configured as described above will be described using examples of {Example 1} to {Example 3}.

{Example 1} As shown in FIG.
Operation when there are a plurality of operations that perform exactly the same operation (1) The operation appearance position detection unit 3 a
7 is detected from the program shown in FIG. 7 and the specified variable g is detected. Further, an operation expression “h = f + 400” having the same operation as the operation “f + 400” on the right side of the equal sign is detected, and a deletion variable h is detected.

(2) The first value use position detection unit 4a receives the deletion variable h from the operation appearance position detection unit 3a, and the rewrite operation expression “*” in which the deletion variable h is used as an operand. a = h * 70 "is detected. (3) The cost extraction unit 7 searches the cost storage unit 5 with the rewrite operation expression “* a = h * 70” detected by the value use position detection unit 4a, and extracts the cost of the machine language instruction corresponding to the operation. And outputs it to the comparison unit 11.

(5) The first rewriting cost extracting unit 8
The designated variable g is received from the calculation appearance position detection unit 3a, and the rewriting operation expression “* a =
h * 70 ”, the deleted variable h in the rewrite operation expression is rewritten to the designated variable g, and the rewritten operation expression“ * a
= G * 40 ", the cost storage unit 5 is searched, and the cost of the arithmetic expression is extracted and output to the comparison unit 11.

(6) The comparing unit 11 receives the costs extracted by the cost extracting unit 7 and the first cost rewriting and extracting unit 8, and compares the costs. In this case, since the cost received from the first rewriting cost extracting unit 8 is small,
The first rewriting unit 12 is started. (7) The first rewriting unit 12 performs the calculation appearance position detection unit 3
The specified variable g is received from a, and the deleted variable h of the rewrite operation expression “* a = h * 70” detected by the first value use position detection unit 4a is rewritten to the specified variable g.

(8) The first arithmetic expression removing unit 13 sets the arithmetic appearance position detecting unit 3a after rewriting by the first rewriting unit 12.
The arithmetic expression “h = f + 400” at the position notified from is deleted from the program. By the above operation, the program shown in FIG. 4 is rewritten to the program shown in FIG. {Example 2} Operation in the case where an arithmetic expression for assigning a variable to a variable and an arithmetic expression for assigning a constant to a variable exist in the program as shown in FIG. 6 (1) The assignment appearance position detection unit 3b is configured as shown in FIG. From the program shown, an arithmetic expression “f = 20” for substituting a constant for a variable is detected.

(2) The second value use position detection unit 4b receives the deletion variable from the substitution appearance position detection unit 3b, and the rewrite operation expression “g = f +” in which the deletion variable is used as an operand. * A ”is detected and output to the second rewriting cost extracting unit 9. (3) The cost extraction unit 7 uses the rewrite operation expression “g = f ++ a” detected by the value use position detection unit 4b to store the cost in the cost storage unit 5.
Is retrieved, and the cost of the machine language instruction corresponding to the operation expression is extracted and output to the comparison unit 11.

(4) The second rewriting cost extracting unit 9
The deletion variable “f” and the designated substitution number “20” are received from the substitution appearance position detection unit 3b, the rewrite operation expression “g = f ++ a” is received from the second value use position detection unit 4b, and the operation expression “g” is received. = F ++ a "to" g = 20 ++ a "
The cost of the machine language instruction corresponding to the rewritten arithmetic expression is extracted and output to the comparison unit 11.

(5) The comparing section 11 receives the costs extracted by the cost extracting section 7 and the second cost rewriting and extracting section 9 and compares them. In this case, the cost taken out by the second cost rewriting / extracting section 9 is small.
Is started. (6) The second rewriting unit 14 performs the substitution appearance position detection unit 3
When the designated substitution number “20” is received from b, the deletion variable “f” in the rewrite operation expression detected by the second value use position detection unit 4b is rewritten to the designated substitution number “20”.

(7) After rewriting by the second rewriting unit 14, the second arithmetic expression removing unit 15 sets the substitution appearance position detecting unit 3b
Is deleted from the program. When the redundant type removing device performs such processing, the program shown in FIG. 6 is rewritten as shown in FIG. {Example 3} As shown in FIG. 8, when there is a description that calculates an address using a variable written as a pointer variable in a program and assigns the contents of the calculated address to the variable (1) Pointer operation The expression detection unit 3c calculates the pointer operation expressions “d = c + 400” and “d1
= C * 400 ".

(2) The third value use position detecting section 4c receives the pointer variables "d" and "d" from the pointer arithmetic expression detecting section 3c.
1 ”and the pointer operation expression“ a = * (b +
d) "and" a = * (b + d1) ". (3) The cost extracting unit 7 is a third value use position detecting unit 4c.
Rewrite arithmetic expressions “a = * (b + d)”, “a
= * (B + d1) ", retrieves the cost of the machine language instruction corresponding to the arithmetic expression, and outputs it to the comparing unit 11.

(4) Third Rewriting Cost Extraction Unit 10
Are designated variables d, d1,.
Receiving the designated operation “c + 400”, “c * 400”,
The third value use position detection unit 4c outputs the rewrite operation expression “a =
* (B + d) "and" a = * (b + d1) ", and delete variables d and d1 in the rewrite operation formula are rewritten to the designated operations" c + 400 "and" c * 400 ", and the rewritten operation expression" a = * (B + c + 400) "," a = * (b
+ C * 400) ", retrieves the cost of the machine language instruction in the addressing mode corresponding to the operation, and outputs it to the comparing unit 11.

(5) The comparing unit 11 receives the costs extracted by the cost extracting unit 7 and the third cost rewriting extracting unit 10, and compares the costs. As a result of the comparison, the cost extracted by the third rewriting cost extracting unit 8 is small, so the third rewriting unit 10 is activated. (6) The third rewriting unit 16 includes the calculation appearance position detection unit 3
The pointer operations “c + 400” and “c * 400” are received from “a”, and the designated variable in the rewrite operation expression detected by the third value use position detection unit 4c is rewritten to the pointer operation.

(7) After the third rewriting unit 16 rewrites, the third operation expression removing unit 17
, The designated arithmetic expression "d = c + 400"
"D1 = c * 400)" is deleted from the program. When such processing is performed, the program shown in FIG. 8 is rewritten as shown in FIG. Note that the configuration of the redundant expression removing device of the present invention is not limited to the above-described configuration. formula)
The cost storage unit 5 is searched with the type of the operation expression of the redundant expression, and the redundant cost extraction unit for extracting the cost corresponding to the type of the operation expression, the cost extracted by the cost extraction unit 7, and the redundant cost extraction unit And a calculating unit for calculating the sum of the costs calculated by the calculating unit.
The cost may be compared with the cost extracted by the first, second, and third rewriting cost extracting units 8, 9, and 10 to determine whether to perform the rewriting and the removal of the redundant expression.

The cost fetching unit 7, the first, second, and third rewriting cost fetching units 8, 9, and 10 calculate the sum of the fetched costs, and the comparison unit 11 compares the sum of the costs thus obtained. Thus, it may be determined whether or not to rewrite or remove the redundant expression. Further, the redundant expression cost extraction unit searches the cost storage unit 5 with the type of the operation expression including the operation located after the second among the operations detected by the operation appearance position detection unit 3a, and The cost corresponding to the type of the formula is extracted, the cost extracting unit 7, the first, second, and third rewriting cost extracting units 8, 9, and 10 calculate the sum of the extracted costs. The cost fetching unit 7 calculates the sum of the fetched cost and the cost fetched by the redundant cost fetching unit, and the cost fetching unit 7 calculates the sum of the cost obtained by the calculation unit and the first, second, and third rewriting cost fetching units 8,
9, 9 and 10 may be compared with the sum of the extracted costs to determine whether to perform rewriting and remove redundant expressions.

[0065]

As described above, according to the redundant expression elimination device of the present invention, the operand of the operation to be processed corresponds to any one of a constant, a register variable, a stack variable, and a static variable. Since the operator is rewritten after comparing the costs before and after the rewriting, the operation can be rewritten only when the rewriting of the operation is valid.

Also, the processor of the target machine is
When addressing modes such as indirect address reference with index and offset, indirect address reference with offset, etc. can be used, rewriting of operations that can effectively use these addressing modes is performed, thus reducing costs. There is an effect that it can be sufficiently achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a redundant removal device 10 according to an embodiment of the present invention.

FIG. 2 is a diagram showing contents of a cost storage unit 5;

FIG. 3 is a diagram showing contents of an addressing cost storage unit 6;

FIG. 4 is a diagram showing a program to be processed;

FIG. 5 is a diagram showing a program rewritten by a redundant-type removing device.

FIG. 6 is a diagram showing a program to be processed;

FIG. 7 is a diagram showing a program rewritten by the redundant-type removing device.

FIG. 8 is a diagram showing a program to be processed;

FIG. 9 is a diagram showing a program rewritten by the redundancy-type removing device.

FIG. 10 is a diagram showing a configuration of a conventional redundant-type removing device that deletes a common sub-expression.

FIG. 11 is a diagram showing a program to be processed;

FIG. 12 is a diagram showing a program rewritten by a conventional redundancy-type removing device.

FIG. 13 is a diagram showing a configuration of a conventional redundant-type removing apparatus that propagates a value.

FIG. 14 is a diagram showing a program to be processed;

FIG. 15 is a diagram showing a program rewritten by a conventional redundant-type removing device.

FIG. 16 is a diagram showing a correspondence between a program and an addressing mode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Control part 3a Operation appearance position detection part 3b Substitution appearance position detection part 3c Pointer operation expression detection part 4a First value use position detection part 4b Second value use position detection part 4c Third value use position detection part 5 Cost Storage unit 6 Addressing cost storage unit 7 Cost extracting unit 8 First rewriting cost extracting unit 9 Second rewriting cost extracting unit 10 Third rewriting cost extracting unit 11 Comparison unit 12 First rewriting unit 13 First arithmetic expression Removal unit 14 Second rewrite unit 15 Second operation expression removal unit 16 Third rewrite unit 17 Third operation expression removal unit 18 Processing target holding unit

Continuation of front page (56) References JP-A-1-214936 (JP, A) JP-A-4-181432 (JP, A) JP-A-5-53822 (JP, A) JP-A-6-119184 (JP) , A) Hisashi Takayama, et al., "Optimal Code Generation by Pattern Matching in Retarable Bleil Compiler" Proc. Of the 28th (1st half of 1984) National Convention of Information Processing Society of Japan (1st volume), Japan, Association of Japan Published by The Information Processing Society of Japan, May 28, 1984, pp. 335-336, (however, the date is the date of receipt of the information center) Masataka Sassa, et. al. , "Optimal Short-Circuit Evaluation of Boolean Expresions", Proc. May 28, pp. 337-338 (however, the date is the date of receipt of the information center). V. Eiho, J.A. D. Ullman, co-authored, Norihisa Doi, translation, "Information Processing Series 7 Compiler", Japan, published by Baifukan Co., Ltd., March 30, 1986, first edition, pp. 366-369, 435-442 V. Aiho (Two others), author, Kenichi Harada, translation, "Compiler II-Hara, Technique, Tool-", Japan, Science Co., Ltd., published, October 10, 1990, first edition, pp. 632-634, 645, 722-725, 729-734 Ikuo Nakata, "Computer-Science Library Compiler", Japan, Sangyo Tosho Co., Ltd., published, September 10, 1981, first edition, pp. 217 (58) Field surveyed (Int.Cl. ⁷ , DB name) G06F 9/45 G06F 9/06 JST file (JOIS) CSDB (Japan Patent Office) INSPEC (DIALOG)

Claims (9)

(57) [Claims] 1. A redundant expression elimination device provided in a compiler for rewriting an operation of a program held in a program holding unit, and removing a redundant operation expression after the rewriting. An operation detecting means for detecting all operations in which a child and an operand are the same, detecting all variables defined by the operation, and storing the position of an operation expression including the detected operation and the variable; Among the variables detected by the detecting means, the second and subsequent variables are used in the operand detecting means for detecting all the operations used as the operands, the type of the arithmetic expression, and the type of the arithmetic expression. A cost storage means for storing the cost of the arithmetic expression corresponding to the type; and a cost storage means for searching the cost storage means by the type of the arithmetic expression detected by the operand detection means, and extracting the cost corresponding to the type of the arithmetic expression The first cost extraction means, and the type of the arithmetic expression when the first variable of the variables detected by the arithmetic detection means is used as the operand of the arithmetic expression detected by the operand detection means. A second cost extracting means for searching the cost storage means and extracting a cost corresponding to the type of the operation expression, a cost extracted by the first cost extracting means, and a cost extracted by the second cost extracting means. As a result of comparison between the comparing means and the comparing means, if the cost fetched by the second cost fetching means is small, in the program of the variable used as the operand in the operation detected by the operand detecting means, A rewriting means for rewriting the position of the operator to the variable detected first by the operation detecting means; and an operand detecting means when the rewriting means rewrites all variables in the operation detected by the operand detecting means. A variable expression removing device for removing, from a program, an arithmetic expression including a variable used as an operand in an operation detected by the method and an operation in which the variable is defined. . 2. The first cost taking means finds the sum of the costs taken out, the second cost taking means finds the sum of the costs taken out, and the comparing means makes the sum of the costs taken out by the first cost taking means. 2. The redundant type removing apparatus according to claim 1, wherein the total cost calculated by said second cost extracting means is compared with the total cost calculated by said second cost extracting means. 3. The redundancy according to claim 1, wherein the comparing means compares the individual costs extracted by the first cost extracting means with the individual costs extracted by the second cost extracting means. Type removal device. 4. A redundant expression eliminator provided in a compiler for rewriting an operation of a program held in a program holding unit and removing a redundant arithmetic expression after the rewriting, wherein the redundant expression elimination device is provided in the program holding unit. From the program
An arithmetic expression that substitutes a constant for a variable, an arithmetic expression detector that detects all the arithmetic expressions that substitute the value of the variable for the variable, and a variable that exists on the left side of the equal sign of the arithmetic expression detected by the arithmetic expression detector , An operand detecting means for detecting from the program holding means all the arithmetic expressions used as operands, the types of the arithmetic expressions, and the costs of the arithmetic expressions corresponding to these types are stored. Cost storage means, first cost extraction means for searching the cost storage means by the type of the arithmetic expression detected by the operand detection means, and extracting the cost corresponding to the type of the arithmetic expression; The cost storage means is searched by the type of the arithmetic expression when the first variable among the variables detected by the arithmetic expression detection means is used as the operand of the detected arithmetic expression,
Second cost extracting means for extracting the cost corresponding to the type of the arithmetic expression, comparing means for comparing the cost extracted by the first cost extracting means with the cost extracted by the second cost extracting means, A comparing unit that compares the cost extracted by the first cost extracting unit with the cost detected by the second cost extracting unit. If the comparison unit determines that the cost extracted by the second cost extracting unit is small, Rewriting means for rewriting the program position of a variable used as an operand in the operation detected by the operand detection means to a variable or constant detected by the arithmetic expression detection means; If the rewriting means rewrites all the variables in the operation, the variable used as the operand in the operation detected by the operand detection means exists on the left side of the equal sign. A redundant expression removing device, comprising: a removing unit that removes, from the program, an operating expression that is an arithmetic expression that is detected by the arithmetic expression detecting unit. 5. The first cost taking means calculates the sum of the taken out costs, the second cost taking out means obtains the sum of the taken out costs, and the comparing means obtains the sum of the taken out costs. 5. The apparatus according to claim 4, wherein the total cost is compared with the total cost obtained by the second cost extracting means. 6. The comparison means for comparing the individual costs extracted by the first cost extraction means with the individual costs extracted by the second cost extraction means.
4. The redundant removing device according to 4 . 7. A redundant expression elimination device provided in a compiler for rewriting an operation of a program stored in a program holding unit and removing a redundant arithmetic expression after the rewriting. An operation detecting means for detecting an arithmetic expression in which a variable which is a pointer is defined, and storing a position of the detected arithmetic operation and an arithmetic expression including the variable; and a variable detected by the operation detecting means being used as an operand. Operand detection means for detecting all of the arithmetic expressions, and an arithmetic expression which can be executed by one machine language instruction and which is used for a pointer, an operand used for an index, and Cost of storing the type of the operand including at least two operands among the operands used for the offset, and the cost of the operation expression corresponding to the type of the operation expression Storage means, first cost extracting means for retrieving the cost storage means with the arithmetic expression detected by the operand detection means and extracting the cost of the arithmetic expression corresponding to the arithmetic expression, and detecting by the operand detecting means Second cost extracting means for retrieving the cost storage means and retrieving the cost corresponding to the arithmetic expression by using the type of the arithmetic expression in the case where the arithmetic operation detected by the arithmetic detecting means is applied to the operand of the calculated arithmetic expression And comparing means for comparing the cost taken out by the first cost taking out means and the cost taken out by the second cost taking out means. As a result of comparison by the comparing means, the cost taken out by the second cost taking out means becomes If it is smaller, rewriting means for rewriting the position in the program of a variable used as an operand in the arithmetic expression detected by the operand detection means to the operation detected by the operation detection means; The variables in all the arithmetic expressions detected by the child detection means are
A redundant expression removing device, comprising: removing means for removing, from a program, an arithmetic expression including an arithmetic operation detected by an arithmetic detecting device when the rewriting device has rewritten. 8. The first cost taking means calculates the sum of the taken out costs, the second cost taking out means obtains the sum of the taken out costs, and the comparing means obtains the sum of the taken out costs. 8. The redundant-type elimination apparatus according to claim 7, wherein the total sum of the costs calculated is compared with the total sum of the costs obtained by the second cost extracting means. 9. The comparing means compares the individual cost extracted by the first cost extracting means with the individual cost extracted by the second cost extracting means.
8. The redundant removing device according to 7 .