JPH04239917A - Information processor with branch history table - Google Patents

Abstract

PURPOSE:To perform the efficient prefetch processing of the branch destination of a branch instruction by preventing output of a forecast address due to erroneous hit information. CONSTITUTION:A virtual computer discriminating information register 7 holds virtual computer discriminating information of virtual computers assigned at present. A branch history table 3 has plural entries each of which consists of virtual computer discriminating information, a branch instruction storage address, and a branch instruction branch destination address. The branch history table 3 is read out at the time of indexing with an index flag 2 on. When the index address of an address register 1 coincides with the read branch instruction storage address and virtual computer discriminating information of a virtual computer discriminating information register 7 coincides with read virtual computer discriminating information, hit information including the read branch instruction branch destination address is outputted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information processing apparatus having a branch history table, and more particularly to an information processing apparatus having a branch history table that stores the history of pairs of branch instruction storage addresses and branch destination addresses in virtual computer systems. Regarding equipment.

0002

2. Description of the Related Art In order to process branch instructions at high speed, an information processing device having a conventional branch history table records the history of pairs of addresses where branch instructions are stored and addresses to which the branch instructions are branched. It has a stored branch history table, which is indexed when reading an instruction, and outputs a predicted value of the branch destination address.

[0003] As a reference for the conventional branch history table, ``Branch prediction
n Strategies and Branc
hTarget Buffer Design”,
J. K. F. Lee, A. J. Smith IEEE
COMPUTER 1984 Jan. There is.

0004

Problems to be Solved by the Invention The information processing device having the conventional branch history table described above has a branch history table that stores the history of pairs of addresses where branch instructions are stored and addresses to which the branch instructions are branched. Although the virtual machine system is equipped with a table, indexed when reading an instruction, and outputs the predicted value of the branch destination address,
Since the same address space is used between different operating systems, an entry in the branch history table registered while one operating system is running may hit the same entry while another operating system is running, resulting in an incorrect address space. It has the disadvantage that outputting the predicted address generates extra overhead in processing branch instructions.

An object of the present invention is to include, in a branch history table, a history of pairs of addresses where branch instructions are stored and addresses of branch destinations of the branch instructions, as well as a history of identification information of virtual machines in operation. Alternatively, the history of the entry number of the stack in which the identification information of the operating virtual machine is stored is stored, and the identification information of the operating virtual machine or the stack in which the identification information of the operating virtual machine is stored at the time of indexing. By outputting hit information including the address of the branch destination of the branch instruction only when the entry number matches the entry number of the branch instruction, it is possible to prevent the output of predicted addresses due to incorrect hit information. An object of the present invention is to provide an information processing device having a branch history table that can perform prefetch processing.

[0006]

[Means for Solving the Problems] An information processing device having a branch history table according to the first invention provides: (A) a virtual machine identifier that holds virtual machine identification information indicating a virtual machine currently allocated in a virtual machine system; information register; (B) a branch history table having a plurality of entries including a valid bit, virtual machine identification information, a branch instruction storage address, and a branch instruction branch destination address; (C) of the branch history table; Upon indexing, the specified index address matches the branch instruction storage address stored in the selected entry of the branch history table only if there is a valid bit stored in the selected entry of the branch history table. At the same time, when the virtual machine identification information held in the virtual machine identification information register matches the virtual machine identification information stored in the selected entry of the branch history table, the selected entry of the branch history table It is configured by outputting hit information including the branch destination address of the branch instruction stored in the .

[0007] Furthermore, the information processing device having the branch history table of the second invention has the following features: (A) Holds virtual machine identification information indicating the currently allocated virtual machine in a virtual machine identification information register of the virtual machine system. (B) The branch history table has a plurality of entries including virtual machine identification information, a branch instruction storage address, and a branch instruction branch destination address; (C) When indexing the branch history table, The index address matches the branch instruction storage address stored in the selected entry of the branch history table, and the virtual machine identification information held in the virtual machine identification information register is the selected entry of the branch history table. When the virtual machine identification information stored in the branch history table matches the virtual machine identification information stored in the branch history table, hit information including the branch destination address of the branch instruction stored in the selected entry of the branch history table is output.

Furthermore, the information processing apparatus having the branch history table of the third invention includes: (A) a virtual machine identification information register that holds virtual machine identification information indicating the virtual machine currently allocated in the virtual machine system; B) a virtual machine identification information stack that stores a plurality of pieces of virtual machine identification information including the virtual machine identification information held in the virtual machine identification information register; (C) a virtual machine identification held in the virtual machine identification information register; a stack entry number register that holds a stack entry number of the virtual machine identification information stack in which information is stored; (D) a plurality of stack entry numbers of the stack entry number register, a branch instruction storage address, and a branch instruction branch destination address; (E) When indexing the branch history table, a specified index address is a branch instruction storage address stored in the selected entry of the branch history table. and the stack entry number held in the stack entry number register matches the stack entry number stored in the selected entry of the branch history table, It is configured by outputting hit information including the stored branch instruction branch destination address.

[0009]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an information processing apparatus having a branch history table according to the first invention.

Virtual machine identification information register 7 shown in FIG.
holds virtual machine identification information indicating the virtual machine currently allocated in the virtual machine system.

Further, the branch history table 3 has a large number of entries including a valid bit Vi, virtual machine identification information Si, a branch instruction storage address Ki, and a branch instruction branch destination address Bi, and stores the history of these entries. There is.

Therefore, when indexing the branch history table 3, the address to be indexed is given from the address register 1 and the index flag 2 is turned on, so that the entry i selected by the lower bit of the address register 1 is read out.

[0014] Then, index flag 2 is turned on and becomes "1".
is sent to the AND gate 6, and "1" is sent to the AND gate 6 only if the valid bit Vi stored in the selected entry i of the branch history table 3 is on.
sent to.

Furthermore, when the comparator 4 matches the virtual machine identification information held in the virtual machine identification information register 7 with the virtual machine identification information Si stored in the selected entry i of the branch history table 3, , "1" is AN
Sent to D Gate 6.

Furthermore, in the comparator 5, the address register 1
When the index address specified by the upper bit of the branch history table 3 matches the branch instruction storage address Ki stored in the selected entry i of the branch history table 3, "1" is sent to the AND gate 6.

As a result, only when the four input conditions of the AND gate 6 are all "1", the AND gate 6
A hit signal H is output. Along with the hit signal H, the branch instruction branch destination address Bi stored in the selected entry i of the branch history table 3 is output as hit information.

FIG. 2 is a block diagram showing an embodiment of an information processing apparatus having a branch history table according to the third invention.

Virtual machine identification information register 1 shown in FIG.
7 holds virtual machine identification information indicating the virtual machine currently allocated in the virtual machine system.

On the other hand, the virtual machine identification information stack 18 stores a plurality of pieces of virtual machine identification information including the virtual machine identification information held in the virtual machine identification information register 17.

[0021] Also, the stack entry number register 19
holds the stack entry number of the virtual machine identification information stack 18 in which the virtual machine identification information held in the virtual machine identification information register 17 is stored.

On the other hand, the branch history table 13 has a large number of entries including a valid bit Vi, a stack entry signal Ei, a branch instruction storage address Ki, and a branch instruction branch destination address Bi, and stores the history of these entries. .

Therefore, when indexing the branch history table 13, the address to be indexed is given from the address register 11 and the index flag 12 is turned on, so that the entry i selected by the lower bit of the address register 11 is read out.

Then, when the index flag 12 is turned on, it becomes “1”.
" is sent to the AND gate 16, and "1" is sent to the AND gate 16 only if the valid bit Vi stored in the selected entry i of the branch history table 13 is on.

Furthermore, the comparator 14 determines that the stack entry number held in the stack entry number register 19 is
When matching the stack entry signal Ei stored in the selected entry i of the branch history table 13,
“1” is sent to AND gate 16.

Furthermore, when the index address specified by the upper bits of the address register 11 matches the branch instruction storage address Ki stored in the selected entry i of the branch history table 13, the comparator 15 determines "
1” is sent to AND gate 16.

As a result, the AND gate 16 outputs the hit signal H only when the four input conditions of the AND gate 16 are all "1". And hit signal H
At the same time, the branch instruction branch destination address Bi stored in the selected entry i of the branch history table 13 is output as hit information.

[0028]

As explained above, the information processing device having the branch history table of the present invention stores in the branch history table the pair of the address where the branch instruction was stored and the address of the branch destination of that branch instruction. In addition to the history, the history of the identification information of the running virtual machine or the history of the stack entry number in which the running virtual machine identification information is stored is stored, and the running virtual machine identification information is stored at the time of indexing. Or, only when the identification information of the running virtual machine matches the entry number of the stack where it is stored,
By outputting hit information that includes the address of the branch destination of a branch instruction, it is possible to prevent a predicted address from being output due to incorrect hit information and to perform efficient prefetch processing for the branch destination of a branch instruction. ing.

In particular, the information processing device having the branch history table of the third invention saves the size of the branch history table by using the stack entry number compared to the first or second invention. This has the effect of reducing the number of expensive high-speed memory elements used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an information processing apparatus having a branch history table according to a first invention.

FIG. 2 is a block diagram showing an embodiment of an information processing apparatus having a branch history table according to a third invention.

[Explanation of symbols]

1, 11 Address register 2, 12 Index flag 3, 13 Branch history table 4, 5, 14,
15 Comparator 6, 16 AND gate 7, 17 Virtual machine identification information register 18
Virtual machine identification information stack 19 Stack entry number register Bi Branch instruction branch destination address Ei Stack entry signal H Hit signal Ki Branch instruction storage address Si Virtual machine identification information

Claims (3)

[Claims] Claim 1: (A) a virtual machine identification information register that holds virtual machine identification information indicating the virtual machine currently allocated in the virtual machine system; (B) a valid bit, virtual machine identification information, and branch instruction storage address; (C) When the branch history table is indexed, the valid bit stored in the selected entry of the branch history table is Only in certain cases, the specified index address matches the branch instruction storage address stored in the selected entry of the branch history table, and the virtual machine identification information held in the virtual machine identification information register is When the virtual machine identification information stored in the selected entry of the branch history table matches, hit information including the branch destination address of the branch instruction stored in the selected entry of the branch history table is output. An information processing device having a characteristic branch history table. Claim 2: (A) The virtual machine identification information register of the virtual machine system holds virtual machine identification information indicating the currently allocated virtual machine, and (B) The branch history table contains the virtual machine identification information and the virtual machine identification information. (C) When indexing the branch history table, a specified index address is stored in a selected entry of the branch history table; when the virtual machine identification information held in the virtual machine identification information register matches the virtual machine identification information stored in the selected entry of the branch history table; An information processing device having a branch history table, characterized in that the information processing device outputs hit information including a branch destination address of a branch instruction stored in a selected entry of the branch history table. 3. (A) a virtual machine identification information register that holds virtual machine identification information indicating a virtual machine currently allocated in a virtual computer system; (B) a virtual machine identification held in the virtual machine identification information register; (C) a stack entry number of the virtual machine identification information stack in which the virtual machine identification information held in the virtual machine identification information register is stored; (D) a branch history table that stores a plurality of entries including a stack entry number of the stack entry number register, a branch instruction storage address, and a branch instruction branch destination address; (E) When indexing the branch history table, the specified index address matches the branch instruction storage address stored in the selected entry of the branch history table, and the stack entry stored in the stack entry number register When the number matches the stack entry number stored in the selected entry of the branch history table, output hit information including the branch instruction branch destination address stored in the selected entry of the branch history table. An information processing device having a branch history table characterized by the following.