Predicting a table of contents pointer value responsive to branching to a subroutine

• US 10,656,946 B2
• Filed: 11/21/2017
• Issued: 05/19/2020
• Est. Priority Date: 09/19/2017
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gschwind, Michael K., Salapura, Valentina
• Primary Examiner(s): Li, Aimee
• Assistant Examiner(s): Carmichael-Moody, Courtney P
• Application Number:
  US15/819,420
• Publication Number:
  US 20190087189A1
• Time in Patent Office: 910 Days
• CPC Class Codes: G06F 8/434 Pointers; Aliasing
• CPC Class Codes: G06F 8/443 Optimisation
• CPC Class Codes: G06F 9/30054 Unconditional branch instructions
• CPC Class Codes: G06F 9/30076 to perform miscellaneous control operations, e.g. NOP
• CPC Class Codes: G06F 9/30101 Special purpose registers
• CPC Class Codes: G06F 9/30123 according to context, e.g. thread buffers
• CPC Class Codes: G06F 9/3017 Runtime instruction translation, e.g. macros
• CPC Class Codes: G06F 9/30181 Instruction operation extension or modification
• CPC Class Codes: G06F 9/325 for loops, e.g. loop detection or loop counter
• CPC Class Codes: G06F 9/35 Indirect addressing
• CPC Class Codes: G06F 9/3557 using program counter as base address
• CPC Class Codes: G06F 9/3832 Value prediction for operands; operand history buffers
• CPC Class Codes: G06F 9/3844 using dynamic branch prediction, e.g. using branch history tables
• CPC Class Codes: G06F 9/3861 Recovery, e.g. branch miss-prediction, exception handling error detection or correction G06F11/00
• CPC Class Codes: G06F 9/4484 Executing subprograms

Abstract

Predicting a Table of Contents (TOC) pointer value responsive to branching to a subroutine. A subroutine is called from a calling module executing on a processor. Based on calling the subroutine, a value of a pointer to a reference data structure, such as a TOC, is predicted. The predicting is performed prior to executing a sequence of one or more instructions in the subroutine to compute the value. The value that is predicted is used to access the reference data structure to obtain a variable value for a variable of the subroutine.

Claims

1. A computer-implemented method of facilitating processing within a computing environment, the computer-implemented method comprising:

calling a subroutine from a calling module executing on a processor;

predicting, based on calling the subroutine, a value of a pointer to a reference data structure, the predicting being performed prior to executing a sequence of one or more instructions in the subroutine to compute the value of the pointer;

determining whether a current instruction in the subroutine corresponds to the sequence of one or more instructions to compute the value of the pointer;

inserting in the code, based on determining the current instruction corresponds to the sequence of one or more instructions to compute the value, a single check instruction to check the prediction of the value, the inserting replacing the sequence of one or more instructions, wherein instructions to compute the value of the pointer are replaced by the single check instruction; and

using the value that is predicted to access the reference data structure to obtain a variable value for a variable of the subroutine.

2. The computer-implemented method of claim 1, further comprising:

obtaining a current value of the pointer prior to the predicting; and

storing the current value in a recovery location.

3. The computer-implemented method of claim 2, further comprising:

determining that the value predicted for the pointer is incorrect; and

obtaining, based on determining the value predicted for the pointer is incorrect, the current value from the recovery location.

4. The computer-implemented method of claim 1, further comprising loading the value predicted for the pointer in a defined location.

5. The computer-implemented method of claim 1, further comprising:

determining whether a check indicator is set; and

determining whether the current instruction corresponds to the sequence of one or more instructions to compute the value, based on determining the check indicator is set.

6. The computer-implemented method of claim 1, further comprising:

determining, based on determining the current instruction does not correspond to the sequence of one or more instructions to compute the value, whether the current instruction corresponds to a sequence of one or more instructions to use the value; and

performing recovery, based at least on determining that the current instruction corresponds to the sequence of one or more instructions to use the value.

7. The computer-implemented method of claim 1, wherein the sequence of one or more instructions comprises a load instruction.

8. The computer-implemented method of claim 1, further comprising:

obtaining a current value of the pointer prior to the predicting; and

storing the current value in a rename register for use in recovery.

9. The computer-implemented method of claim 1, wherein the predicting comprises using a reference data structure pointer cache to obtain the value.

10. The computer-implemented method of claim 1, further comprising:

determining using the single check instruction whether the value that is predicted is correct; and

performing the using based on determining that the value that is predicted is correct.