JPH08272621A - Function call processing method for securing dynamic memory area - Google Patents

Abstract

PURPOSE: To improve the execution performance for securing a dynamic memory area which emerges in a source program through the processing of a compiler. CONSTITUTION: A malloc function retrieval part 1 retrieves a source program and detects a sentence where a malloc function is called out. A data flow analysis part 2 analyzes the data flow of a variable emerging in the source program and defines both defining and using points of every variable. A dynamic memory area using range analysis part 3 traces the using point of the variable that shows the head address of the memory area secured by the malloc function based on the obtained data flow information and then detects a free function call sentence that opens the memory area. A function conversion part 4 converts a pair of malloc and free functions included in the same processing function into a function that secures a dynamic memory area through a stack operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compiler for compiling a source program including a function call statement for dynamically allocating a memory area.

[0002]

2. Description of the Related Art Conventionally, when a program needs to dynamically reserve a memory area, a function for allocating a memory area based on a heap operation prepared by a library of the programming language or an operating system is called. After allocating a memory area and using that memory area in a program, a function that releases the memory area was called.

Further, by dynamically allocating a memory area in the function stack, the memory area is released together with the local variable area in the function at the end of the processing function to facilitate the release processing, and the heap operation is performed. There is also a library that performs processing faster than the dynamic memory area allocation processing based on it. A representative of this library is the alloca function.

[0004]

A function for allocating and releasing a dynamic memory area based on heap operations requires a lot of processing time as compared with a process for allocating a static memory area for calling an operating system. There is a problem that requires. Here, the static memory area is a memory area secured by defining variables in the program.

The function for allocating the dynamic memory area in the stack can be processed at a higher speed than the function for allocating the dynamic memory area based on heap operation because the operating system does not intervene. Since the stack disappears when the executed program processing function ends, the memory area cannot be used beyond the processing function. Therefore, it is necessary to consider the effective range of the dynamic memory area secured by the user's judgment.

An object of the present invention is to improve the execution performance of the process of securing the dynamic memory area appearing in the source program by the process of the compiler.

[0007]

According to the present invention, a function call for dynamically allocating a memory area based on a heap operation by a process of a compiler and a function call for allocating the reserved memory area are provided in a source program. When it is detected that it is located in the same function, both function call statements are combined and converted into a function call statement that dynamically allocates a memory area in the function stack. A method for processing a function call that allocates a dynamic memory area. Is characterized by.

[0008]

When a function call for dynamically allocating a memory area based on a heap operation and a function call for allocating a memory area located in the same function in the source program are detected, the dynamic memory is detected. Since we have found room to speed up the process of allocating the area, both function call statements are grouped together and converted into a function call statement that dynamically allocates a memory area in the function stack. Execution performance can be improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a part of a compiler that inputs a source program written in C language and outputs an object program, and a mall that secures a dynamic memory area.
It is a figure which shows the structure of the part which processes the oc function and the free function which releases a dynamic memory area. The malloc function search unit 1 searches the source program to find the malloc function.
This is the part that finds the statement in which the function is called. The data flow analysis unit 2 analyzes the data flow of variables appearing in the source program to clarify the definition points and usage points of each variable. The dynamic memory area usage range analysis unit 3 traces the usage point of the variable indicating the start address of the memory area secured by the malloc function using the data flow information obtained as a result of the data flow analysis, and releases this memory area. Search the source program for the free function,
Find the statement in which the free function that releases this memory area is called. When the malloc function and the free function corresponding to this malloc function exist in the same processing function, the function conversion unit 4 converts the pair of the malloc function and the free function into a function that secures a dynamic memory area by stack operation. Convert. The compiler is a type of program stored and executed in the storage device of the information processing device.

FIG. 2 is a diagram showing an example of a source program written in C language. Statement 5 is a statement that calls the malloc function, and specifies that a dynamic memory area of 200 bytes is secured and the start address thereof is assigned to the variable a. Statement 6 specifies that the value of variable a is assigned to variable b. Statement 7 specifies to release the dynamic memory area whose start address is indicated by the variable b.

The operation of the compiler shown in FIG. 1 will be described in detail below with reference to the source program shown in FIG.

The alloc function search unit 1 searches the source program for a statement 5 in which the alloc function is called, and from the found statement 5, the head of the dynamically secured memory area which is the return value of the alloc function. Find the variable to which the address is assigned. In the example of FIG. 2, the variable a
Is.

The data flow analysis unit 2 analyzes the data flow of variables appearing in the source program. This method is described, for example, in A. Aho, R.A. Sethi,
J. "Compilers Pri", co-authored by Ullman
nciples, Techniques, and To
ls ". Let S be an arbitrary statement in the source program, and let GEN [S] be a set of variables whose values change by executing the statement S. Variables and statements defined by the statement S The arguments of the function called by S are included in GEN [S]. Further, a set of variables that are defined before sentence S and are also defined by sentence S is KILL [S]. IN a previously defined set of variables
[S]. In addition, the effective set of variables up to the sentence S is OU
When T [S], OUT [S] is obtained by the following data flow equation. OUT [S] = GEN [S] ∪ (IN [S] -KILL
[S]) For example, in sentence 5, GEN [S] is a, KILL
[S] is a and IN [S] is a, b, and c, so OU
T [S] is a, b, and c. About sentence S OUT
Since the variable obtained in [S] is a set of valid variables, the variables included in the set and defined by the statement S and the variables to be used are determined. In this way, the data flow analysis unit 2 arranges the variables defined in each sentence and the used variables according to the control flow for all the sentences in the source program. This reveals the definition and use points of all variables. When the processing function is calling another function, the data flow is similarly analyzed for variables appearing in another function program. Next, the data flow analysis unit 2 uses a variable to which the start address of the dynamic memory area is assigned based on such data flow information to redefine another variable, that is, to assign to another variable. Search for the sentence that does. If there is a statement that does the substitution, find the definition variable of the statement, and similarly search for the use of this variable. In this way, the data flow information about the head address variable is extracted. In the example of FIG. 2, there is an assignment from the variable a to the variable b in the statement 6 for the variable a defined in the statement 5, and further in the statement 7 the variable b.
There is use of. FIG. 3 shows data flow information composed of a series of statements from the definition of the variable a to the use of the variable b. (1), (2) and (3) are sentences respectively.

The dynamic memory area usage range analysis unit 3 searches the source program based on the data flow information of the head address variable obtained by the data flow analysis unit 2, and the statement at the point of use of the variable is the dynamic memory. Free to release area
Check whether it is a function call statement. Even when the processing function is calling another function, the source program is searched in the same manner to find the location of the related free function call statement. In the example of FIG. 2, it is found that the sentence 7 corresponding to the sentence (3) of FIG. 3 is a free function calling sentence. When the free function corresponding to the malloc function is found, it is checked whether or not the existing processing functions of the malloc function and the free function are the same, and if it is found that they are the same, conversion of the malloc function is possible. Judge that there is.

The function conversion unit 4 converts the convertible malloc function call statement obtained by the dynamic memory area use range analysis unit 3 into a process for securing a dynamic memory area by stack operation. In addition, the corresponding free function is deleted. In the example of FIG. 2, the sentence 5 is changed to a = alloca (200) and the sentence 7 is deleted. If the free function corresponding to the malloc function cannot be found, or m
When the processing function in which the free function corresponding to the olloc function exists is different, the processing ends without conversion.

The above processing is performed for all malloc functions.

[0018]

According to the present invention, the compiler converts the function call for allocating and releasing the dynamic memory area based on the heap operation appearing in the source program into the dynamic memory area allocating process by the high speed stack. , It is possible to improve the execution performance of a program that uses the dynamic memory area without the user being aware of it.

[Brief description of drawings]

FIG. 1 is a diagram showing a partial configuration of a compiler according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a source program.

FIG. 3 is a diagram showing an example of data flow information of a head address variable of a memory area.

[Explanation of symbols]

1 ... malloc function search unit, 2 ... data flow analysis unit, 3 ... dynamic memory area usage range analysis unit, 4
... Function conversion unit

Claims (1)

[Claims] 1. Processing by a compiler of a source program including a first function call statement for dynamically allocating a memory area based on a heap operation or a second function call statement for allocating a dynamic memory area in a function stack. In the method, data flow information about a statement to be redefined, which is used through the source program for a variable that defines a start address of a dynamic memory area specified by the first function call statement, is obtained, and A third statement that is a contained statement and releases the memory area secured by the first function call statement
Of the first function call statement and the third function call statement are located in the same function, the first function call statement is converted into the second function call statement, and the third function call statement is converted to the third function call statement. A method for processing a function call that secures a dynamic memory area, characterized by deleting a function call statement.