JP3239830B2 - Transfer instruction optimization apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optimization of an instruction sequence or an intermediate text sequence generated from a source program by a compiler, and more particularly to a transfer instruction optimizing apparatus and method for deleting a transfer instruction.

[0002]

2. Description of the Related Art According to Norihisa Doi, "Compiler", Bundokan, pages 440 to 442, which is a reference on compiler optimization, a transfer instruction (a simple assignment process in the form of A = B, A process of copying the value of a storage area such as a register or a memory on the right side or a constant value “B” into a storage area “A” such as a register or a memory) includes a copy propagation means as an optimization technique in a compiler for reduction. This optimization technique eliminates the need for a transfer instruction by replacing all references to the left operand A of the transfer instruction following the transfer instruction (A = B) with the value of the right operand B,
It was a method to reduce the transfer orders. For example, the transfer instruction (A = B) is deleted by replacing the value of the operand A with the operand B, as shown below as an example of the instruction sequence before the copy propagation processing and after the copy propagation processing. Is implemented.

Instruction sequence before copy propagation process Instruction sequence after copy propagation process A = B (deleted) X = A + C X = B + CY Y = A / 2.0 Y = B / 2.0 Is described in JP-A-4-17031. The copy propagation system described in this publication is an example in which the right side of a transfer instruction is a constant, and the unnecessary transfer instruction is reduced by replacing the reference of the value on the left side after the transfer instruction with the constant value on the right side. is there. As described above, the conventional copy propagation method is performed by replacing the reference of the operand on the left side of the transfer instruction with the operand on the right side.

[0004]

A first problem is that the pattern of an instruction sequence from which a transfer instruction can be deleted is limited. The reason is that if a new definition instruction for the right-hand operand appears before all references to the left-hand operand of the transfer instruction are replaced by the right-hand operand, the value of the right-hand operand is changed, and the value at the time of the transfer instruction is changed. Therefore, the left operand cannot be replaced after the definition instruction, and as a result, the transfer instruction cannot be deleted. The following is an example of an instruction sequence in which a transfer instruction cannot be deleted by the conventional copy propagation method.

A = B B = X / 2.0 Y = A + C The value of the operand A of the third instruction (Y = A + C) cannot be replaced by the operand B (the second instruction B = X / 2.0 Since the value of the operand B has been changed), the transfer instruction A = B cannot be deleted.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus and a method for determining, when a definition instruction on the right-hand side of a transfer instruction appears in an instruction sequence including the transfer instruction, a condition under which the transfer instruction can be deleted and deleting the same. It is.

[0007]

SUMMARY OF THE INVENTION A transfer instruction optimizing apparatus and method for deleting a transfer instruction according to the present invention does not replace the reference of the left-hand operand of the transfer instruction with the right-hand operand. Replace the reference with the left operand. For this reason, the copy propagation processing means for deleting the transfer instruction finds the definition instruction of the right-hand operand of the transfer instruction to be newly deleted, and can replace the transfer instruction with the left-hand operand of the transfer instruction in the instruction sequence after the transfer instruction? Extended copy propagation processing means for determining whether or not the instruction has been scanned, performing a replacement determination process and a replacement process for the right-hand operand by the left-hand operand while scanning all the instruction strings, and deleting the transfer instruction when all the replacement processes are completed. Is added. The extended copy propagation processing means replaces the left side operand in the definition text of the right side operand of the transfer instruction with the left side operand of the transfer instruction while deleting the transfer instruction. The transfer instruction is deleted by replacing all references to the right-hand operand with the left-hand operand. Further, the value of the left operand of the transfer instruction is changed so as to be calculated by the definition instruction of the right operand. For this reason, even if a new definition instruction of the right-hand operand appears and the value of the right-hand operand is changed, the value of the left-hand operand of the transfer instruction referred to thereafter is obtained as a result of the definition instruction of the right-hand operand. The transfer instruction can be deleted without performing operand replacement.

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings. Referring to FIG. 1 showing the configuration of an embodiment of a transfer instruction optimizing apparatus, a source program 1 for holding a source program file and an intermediate program for inputting a source program and performing lexical analysis and syntax analysis to generate an intermediate text A program generating means 2, an intermediate program 3 for holding the generated intermediate text, an intermediate text optimizing means 4 for inputting the intermediate text and converting it to an optimized intermediate text, and inputting the optimized intermediate text And a target program generating means 5 for converting the target program into a target program, and a target program 6 for holding the target program.

The intermediate text optimizing means 4 performs general text sequence optimization such as common expression deletion processing and invariant expression moving out of the loop with respect to the intermediate text sequence in the intermediate program 3. It comprises a copy propagation processing means 41 for performing conventional copy propagation processing, and an extended copy propagation processing means 42 for extending the transfer instruction deletion target according to the present invention. The intermediate text that performs a transfer instruction that has not been optimized by the conventional copy propagation processing means 41 becomes the text to be deleted after the extended copy propagation processing means 42 determines the deletion condition.

Next, the operation of the embodiment of the present invention will be described with reference to FIG. In FIG. 1, a source program 1 is converted into an intermediate text string by an intermediate program generating means 2 of a compiler, and is stored in an intermediate program 3. The intermediate text string in the intermediate program 3 is optimized by the intermediate text optimizing means 4. The transfer instruction in the intermediate text string becomes the target text of the copy propagation processing means 41, and the deletion condition is determined and deleted if possible. The transfer instruction that could not be deleted becomes the target text of the extended copy propagation processing means 42.

FIG. 2 shows the flow of processing of the extended copy propagation processing means 42 in which the conditions for applying the transfer instruction deletion according to the present invention are extended. In the figure, the transfer text (instruction) indicates the definition text (instruction) for determining the value of the right operand of the transfer text, and the definition text (instruction) of the right operand of the transfer text appearing after the transfer text. ing. To explain the inventions of the processing of this with reference to FIG. 2. If a transfer text that were not removed by the copy propagation process unit 41 (step 21), found from the front of the middle text column definition text that determines the value of the right-hand operand transfer text (Step 2
2). If the definition text is not found, the subsequent processing is interrupted and the processing ends. If the definition text is found, it is checked whether or not the left operand is used in the intermediate text between (step 23).
If the left and right operands are used,
Since the optimization cannot be performed, the subsequent processing is interrupted and terminated.
If the left and right operands are not used,
The next text is taken out and the flag DEF_FLAG is set to "0" (step 24). Subsequent step 2
The processes from 5 to 31 are repeated until there is no intermediate text or a new definition text of the right-hand operand appears. In the extracted intermediate text, it is determined whether or not (step 2
5). If not a definition text (YE in step 25)
S), it is determined whether or not the text is a definition text of the left operand (step 26). If it is not a definition text (NO in step 26), the process proceeds to step 28. If the text is a definition text (YES in step 26), “1” is set in the flag DEF_FLAG, and the flow advances to step 28. In step 28, it is determined whether or not the current intermediate text is the reference text of the right-hand side operand. If it is not a reference text (NO in step 28), the process proceeds to step 31. Reference text (step 28
If the flag DEF_FLAG is already "1" (YES in step 29), the process is interrupted and the optimization is terminated. If DEF_FLAG is not "1" (NO in step 29), the reference of the right-hand operand in the current intermediate text is replaced with the reference of the left-hand operand (step 30). In step 31, the text following the current intermediate text is extracted, and the processing from step 25 is repeated. In step 25, if the intermediate text disappears or the text of appears, the process proceeds to step 32. In step 32, the left operand is replaced with the left operand, and the transition text is deleted.

Next, the operation of this embodiment will be described with reference to FIG.
This will be described with reference to specific examples of FIGS. 3 (a), 3 (b) and 3 (c).
FIG. 3A shows an intermediate text string 51 that includes a transition text that cannot be deleted by the copy propagation processing unit 41 and is a target of the extended copy propagation processing unit 42. Since there is a definition text of the right operand between the transfer text and the reference text of the left operand, it cannot be deleted by the conventional copy propagation processing. First, in step 22, the definition text of the right-hand operand B of the transfer text is found. The found definition text is (B = C * 2.
0). Is not used, the operand A and the operand B are not used.
And the process proceeds to step 24. The next text in step 25, that is, (Z = B / 2.0) is extracted and the subsequent processing is performed. Is not the definition text of the right-hand operand B of step 25, so that the result of step 25 is YES, and the routine goes to step 26. Further, since is not the definition text of the operand A on the left-hand side, the result is NO, and the flow shifts to step 28. Refers to the operand B on the right side of, but since the flag DEF_FLAG remains “0”, the flow proceeds to step 30. Here, the reference of the operand B is changed to the reference of the operand A. The intermediate text string at this point is the replacement text string 52 in FIG.

Next, the next text in step 31 is taken out, and steps 25 to 31 are performed in the same manner. When the intermediate text is extracted, since the text is the definition text of the right-hand operand B, step 25 is NO and the process proceeds to step 32. here,
Replace the left-hand operand B with the left-hand operand A and delete the transport text. The intermediate text string at this point is the deleted text string 53 in FIG.

[0014]

The first effect is that the transfer instruction can be deleted even if the definition text of the right-hand operand of the transfer instruction appears in the (instruction) text string including the transfer (instruction) text. This makes it possible to generate an efficient target program from which unnecessary transfer instructions have been deleted in the optimization of the compiler.

The reason is that the reference to the operand on the right side of the transfer instruction in the instruction sequence after the transfer instruction is replaced by the operand on the left side of the transfer instruction, and the left operand in the definition instruction of the right side operand is replaced by the left operand of the transfer instruction. This is because replacement is performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing the operation of an extended copy propagation processing means of FIG. 1;

FIG. 3 is a diagram illustrating optimization of an intermediate text string including a transfer instruction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Primitive program 2 Intermediate program generating means 3 Intermediate program 4 Intermediate text optimizing means 5 Object program generating means 6 Object program 41 Copy propagation processing means 42 Extended copy propagation processing means

Claims (3)

(57) [Claims] 1. Compiling a source program,
Intermediate program file that generates and accumulates quist stringsTo
Intermediate program generation means to generateAnd determining the delete condition of the transfer instruction from the intermediate text string,
Delete transport instructions that can be deletedHas copy propagation processing means
ToIntermediate text optimizing means;
And a target program generating means for generating a target program.Transfer instruction optimizationIn the device,The copy propagation processing means, Not deleted For the transfer instruction, the transfer instructionMore backward
In the middle text string of the right-hand side operand of the transfer instruction
Is replaced with the operand on the left side of the transfer instruction,
Transfer instructionMore forwardIn the intermediate text string, the transport instruction
The definition instruction of the right-hand operand of
Replace the left operand with the left operand of the transfer instruction
Extended copy propagation processing means for deleting the transfer instruction.
A transfer instruction optimizing device, comprising: 2. Compiling a source program, generating an intermediate text string and storing it in an intermediate program file ,
To determine the deletion condition of the transfer instructions from the intermediate text string,
A method of optimizing a transfer instruction by a copy propagation process for deleting a transfer instruction that can be deleted, the method comprising:
In the intermediate text string ahead of the transfer instruction,
There is a definition instruction for the operand on the right side of the
The operands on the right and left sides of the instruction
When not used during a transfer order, or when said transfer order
In the intermediate text string further behind, the left-hand operation
There is no land definition command, and the right side operation of the transfer command
When the instruction is a land reference instruction, the left
The transfer instruction for the land and the right-hand operand of the reference instruction.
Replace with the left operand of the instruction and delete the transfer instruction
A transfer instruction optimizing method characterized by executing an extended copy propagation process . 3. A computer-readable storage medium for storing a program for executing the extended copy propagation process according to claim 2 .