Patent Application
20060150171
A processor has an instruction set. Software programmers may write assembly language instructions that are translated by an assembler tool into machine language instructions belonging to the instruction set. Alternatively, software programmers may write programs in a higher-level language that are compiled by a compiler into assembly language instructions. Machine language instructions to be executed in parallel by the various functional units of the processor may be combined in an instruction packet. It is generally desirable to reduce the size of the machine language code stored in a program memory accessed by the processor. It may also be desirable to increase the instruction parallelism of the processor.
Embodiments of the invention are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like reference numerals indicate corresponding, analogous or similar elements, and in which:
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity.
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.
Processor 110 has an instruction set. A software programmer may write a program in assembly language, Alternatively, a software programmer may write a program in a higher-level language, and a compiler tool will convert the program to assembly language. An assembler tool will convert the assembly language program to machine language. The compiler tool may build “instruction packets” of assembly language instructions. The assembler tool will convert these instruction packets to packets of machine language instructions belonging to the instruction set, and control words. The machine language instructions in an instruction packet are to be executed in parallel by processor 110. The control words may affect the execution of one or more of the machine language instructions.
Program memory controller 126 may retrieve instruction packets from program memory 108 and provide them to PCU 116. For example, in each clock cycle, PCU 116 may retrieve an instruction packet from program memory 108.
Control words may affect the execution of machine language instructions in the processor in different ways, including, for example:
Dispatcher 140 receives the instruction packet, identifies its entries (machine language instructions and control words), and sends each operation, its operands, and any extensions, to the appropriate functional unit of DAAU 118 or CBU 120 or to sequencer 138.
Both the assembler tool and dispatcher 140 work with a predefined framework regarding permissible formats of instruction packets and a predefined coding scheme for the machine language instructions and control words. A control word may include identification bits and content bits. The content bits may include one or more extension fields. According to embodiments of the present invention, the predefined framework may have one or more of the following properties:
In the following examples, instruction packets have at most 256 bits, machine language instructions are 32-bit instructions or 16-bit instructions, and control words are 32-bit control words or 16-bit control words. An instruction packet may include up to eight entries (machine language instructions and/or control words), regardless of their size. Consequently, if an assembler tool or compiler tool uses 16-bit control words rather than 32-bit control words whenever possible, this may reduce the code size. Furthermore, in the following example, 6 or 8 bits of the control word are used to identify the control word, and the native data width of operands is 32 bits. However, in other embodiments, other sizes of control words, machine language instructions and instruction packets may be used. Similarly, in other embodiments, the maximum number of entries per instruction packet may be different. Similarly, in other embodiments, different native data widths or a configurable native data width is possible. Similarly, in other embodiments, the number of identification bits in a control word may be different.
Extension of Operands
Control words may be used to extend an operand that is partially encoded in a machine language instruction. A non-exhaustive list of such operands includes immediate operands and address operands.
Extension of Address Operands
The number of bits allocated in a machine language instruction for a value of an address operand may be less than the processor address width. For example, a 32-bit machine language instruction format may have 6 bits allocated for encoding an address operand, such as the target address of a branch operation. If the number of bits required to represent the value of a particular address operand does not exceed the number of bits allocated in the machine language instruction format for an address operand, then a single machine language instruction may have sufficient bits to encode the address operand. In this respect, the control word is not needed. However, if the number of bits required to represent the value of the particular address operand exceeds the number of bits allocated in the machine language instruction format for encoding an address operand, then a control word may be used to aid in the encoding of the address operand. For example, least significant bits of the address operand may be encoded in the machine language instruction, and higher-order bits of the address operand may be encoded in a control word.
Extension of Immediate Operands
The number of bits allocated in a machine language instruction for a value of an immediate operand may be less than the native data width. For example, a 32-bit machine language instruction format may have 6 bits allocated for encoding of an immediate operand. If the number of bits required to represent the value of a particular immediate operand does not exceed the number of bits allocated in the machine language instruction format for an immediate operand, then a single machine language instruction may have sufficient bits to encode the immediate operand. In this respect, the control word is not needed. However, if the number of bits required to represent the value of the particular immediate operand exceeds the number of bits allocated in the machine language instruction format for an immediate operand, then a control word may be used to aid in the encoding of the immediate operand. For example, least significant bits of the immediate operand may be encoded in the machine language instruction, and higher-order bits of the immediate operand may be encoded in a control word.
The use of short control words instead of long control words may reduce the code size. For certain specific instruction packets, a short control word has enough content bits to support a particular feature to control one or more of the machine language instructions in that specific instruction packet. For example, if the value of an immediate operand is greater than 6 bits (which are allocated in the instruction) but does not exceed 16 bits, a 16-bit control word (that has 10 content bits) will suffice. However, for other instruction packets, the short control word might not have enough content bits to support that same particular feature to control one or more of the machine language instructions of the other instruction packets. For example if the value of an immediate operand exceeds 16 bits, a 16-bit control word will not suffice.
The size of the control word depends on how many additional bits of the immediate operand one needs in order to fully encode the immediate operand, and that number depends on a) the native data width, b) the number of bits allocated in the machine language instruction format for encoding an immediate operand, and c) the number of bits that are needed to encode the value of the specific immediate operand that is used in the specific instruction.
If the same machine language instructions are to be used in different processors having different native data widths, then the number of bits allocated in the machine language instruction format for, encoding an immediate operand may be the same for those different processors This number of bits may be less than some of the native data widths, and in such cases, the minimum number of content bits of the control word is dependent on the native data width. The control words described herein may therefore be considered to be scalable with respect to the native data width.
Extension of Operations
Control words may be used to extend an operation that is partially encoded in a machine language instruction. For example, a machine language instruction representing the assembly language instruction
add a0, a1, a2
may be extended by a control word that includes a bit that indicates that the extended instruction is to add the value 1 to the contents of register a0 and the contents of register a1 and to store the sum in register a2.
Extension of Conditions
Control words may be used to extend a condition code that is partially encoded in a machine language instruction. The control word extends the partially encoded condition code to a full condition code.
Single Control Word Includes Extensions for Two or More Instructions
Extension fields for two or more instructions may be included in the same control word.
Linkage Between Control Words and Instructions
According to some embodiments of the invention, the connection between control words and instructions may depend on their relative location in the instruction packet. Moreover, the instructions do not need to include an indication of the presence of an extension field in the instruction packet, nor does the control word need to include an identification of the functional unit whose instruction is being extended. Different linkage frameworks are possible.
One exemplary linkage framework is illustrated in
Rule (i) is illustrated in
Rule (i) is also illustrated in
Rule (ii) is illustrated in
Rule (iii) is illustrated by
A different exemplary linkage framework is illustrated in
Multiple Computation Clusters
Returning briefly to
Instruction Replication
To enable processor 110 to execute the same instruction concurrently on different data, commonly known as single-instruction-multiple-data (SIMD), an instruction replication feature may be implemented. The instruction replication feature may reduce the code size of the machine language code, and/or may enable an increase in the number of instructions executed per cycle by processor 110.
The instruction replication feature may make use of an instruction replication control word. As with other control words, an instruction replication control word includes identification bits and content bits. If, for example, each computation cluster includes four functional units, denoted <<1>>, <<2>>, <<3>> and <<4>>, then the content bits of the instruction replication control word may include a 12-bit mask, one bit for each functional unit of clusters “B”, “C” and “D”:
Each valid bit in the bit mask determines whether that particular functional unit of a “slave” cluster is to replicate an instruction for a corresponding functional unit in a “master” cluster “A”. The machine language instructions refer to the functional units of the master cluster. The assembly language instructions may refer to any of the master cluster and the slave clusters, which are additional clusters in the processor. Through the use of the instruction replication control word, machine language instructions that refer to functional units of the master cluster are replicated in the processor so that they are executed also by functional units of one or more of the slave clusters, in order to accurately implement the assembly language instructions. The 12-bit mask includes one bit per functional unit for each of the three “slave” clusters. It is obvious to a person of ordinary skill in the art how to modify the instruction replication control word for a different number of clusters and/or a different number of functional units per cluster. Moreover, the bits of the bit mask need not be consecutive within the instruction replication control word, and the bits of the bit mask may be in any predefined order.
For example, the assembly language program may include the following instructions to be executed in parallel:
add a0, #5, a1||add b0, #5, b1||add c0, #5, c1||add d0, #5, d1
OR
A.add a0, #5, a1||B.add b0, #5, b1||C.add c0, #5, c1||D.add d0, #5, d1
In this example, the software programmer has indicated that in cluster “A”, the immediate operand #5 is to be added to the contents of register a0 and the sum is to be stored in register a1. Similarly, in cluster “B”, the immediate operand #5 is to be added to the contents of register b0 and the sum is to be stored in register b1. Similarly for clusters “C” and “D”. The assembler tool may determine which cluster is to execute which operation by identifying to which cluster the destination register belongs in each of the assembly language instructions. Alternatively, the assembly language instruction may explicitly identify which cluster is to execute which operation.
The assembler tool may identify that these parallel assembly language instructions use the same operation, namely “add”, the same immediate operand, namely #5, and the same indices of the registers. The assembler tool may therefore use the instruction replication feature to generate an instruction packet having a single machine language instruction for “add a0, #5, a1” and an instruction replication control word to indicate that the machine language instruction is to be replicated in clusters “B”, “C” and “D”. The instruction packet may include additional machine language instructions and control words
For example, the machine language instruction for “add a0, #5, a1” may include one or more bits that indicate that the “add” operation is to be executed by the functional unit <<1>> of cluster “A”. The instruction replication control word may include a bit mask to indicate that the corresponding functional units of clusters “B”, “C” and “D” are to execute the replicated instruction. In the example of the instruction replication control word given hereinabove, the 12-bit mask is 100010001000.
In another example, the assembly language program may include the following assembly language instructions to be executed in parallel:
add a0, a1, a2||sub a7, a8, a9||add b0, b1, b2||sub b7, b8, b9
In this example, the software programmer has indicated that in cluster “A”, the contents of registers a0 and a1 are to be added and the sum is to be stored in register a2, and the contents of register a7 are to be subtracted from the contents of register a8 and the difference is to be stored in register a9. Similarly, in cluster “B”, the contents of registers b0 and b1 are to be added and the sum is to be stored in register b2, and the contents of register b7 are to be subtracted from the contents of register b8 and the difference is to be stored in register b9.
The assembler tool may identify that there are two parallel assembly language instructions that use the same operation, namely “add” and the same indices of the operands, and two parallel assembly language instructions that use the same operation, namely “sub” and the same indices of the operands. The assembler tool may therefore use the instruction replication feature to generate an instruction packet having one single machine language instruction for “add a0, a1, a2”, another single machine language instruction for “sub a7, a8, a9” and a control word to indicate that these machine language instructions are to be replicated in cluster “B”. The instruction packet may include additional machine language instructions and control words.
For example, the machine language instruction for “add a0, a1, a2” may include one or more bits that indicate that the “add” operation is to be executed by the functional unit <<1>> of cluster “A”, and the machine language instruction for “sub a7, a8, a9” may include one or more bits that indicate that the “sub” operation is to be executed by the functional unit <<3>> of cluster “A”. The instruction replication control word may include a bit mask to indicate that the corresponding functional units of cluster “B” are to execute the replicated instructions. In the example of instruction replication control word given hereinabove, the 12-bit mask is 101000000000. Dispatcher 140 will interpret this bit mask as meaning that the machine language instruction in the instruction packet for the functional unit <<1>> of cluster “A” is to be replicated in the functional unit <<1>> of cluster “B”, and the machine language instruction in the instruction packet for functional unit <<3>> of cluster “A” is to be replicated in the functional unit <<3>> of cluster “B”.
The machine language instruction format may include one or more bits to indicate that an instruction is to be executed in cluster “A” or cluster “B”. In such a case, the assembler tool could have converted the assembly language instructions
add a0, a1, a2||sub a7, a8, a9||add b0, b1, b2||sub b7, b8, b9
into four separate machine language instructions. However, assuming that machine language instructions are larger than or the same size as control words, using four separate machine language instructions requires more bits than using the instruction replication feature. With the instruction replication feature, the assembler tool may generate an instruction packet having two machine language instructions and one control word.
In yet another example, the assembly language program may include the following assembly language instructions to be executed in parallel:
In this example, the software programmer has indicated that in cluster “A”, the contents of registers a0 and a1 are to be added and the sum is to be stored in register a2, the contents of register a7 are to be subtracted from the contents of register a5 and the difference is to be stored in register a12, the contents of register a14 are to be XORed with the contents of register a15 and the result is to be stored in register a9, and register a13 is to be shifted according to the value of the contents of register a8. In cluster “B”, the contents of registers b0 and b1 are to be added and the sum is to be stored in register b2. In cluster “C”, the contents of registers c0 and c1 are to be added and the sum is to be stored in register c2, and the contents of register c7 are to be subtracted from the contents of register c5 and the difference is to be stored in register c12. In cluster “D”, the contents of registers d0 and d1 are to be added and the sum is to be stored in register d2, the contents of register d7 are to be subtracted from the contents of register d5 and the difference is to be stored in register d12, and the contents of register d14 are to be XORed with the contents of register d15 and the result is to be stored in register d9.
The assembler tool may identify the parallel assembly language instructions that use the same operation and the same indices of the operands. The assembler tool may therefore use the instruction replication feature to generate an instruction packet having one single machine language instruction for “add a0, a1, a2”, another single machine language instruction for “sub a7, a5, a12”, another single machine language instruction for “xor a14, a15, a9”, a control word to indicate that these machine language instructions are to be replicated selectively in clusters “B”, “C” and “D”, and another machine language instruction for “shift a8, a13”. The instruction packet may include additional machine language instructions and control words.
For example, the machine language instruction for “add a0, a1, a2” may include one or more bits that indicate that the “add” operation is to be executed by the functional unit <<1>> of cluster “A”, the machine language instruction for “sub a7, a5, a12” may include one or more bits that indicate that the “sub” operation is to be executed by the functional unit <<2>> of cluster “A”, the machine language instruction for “xor a14, a15, a9” may include one or more bits that indicate that the “xor” operation is to be executed by the functional unit <<3>> of cluster “A”, and the machine language instruction for “shift a8, a13” may include one or more bits that indicate that the “shift” operation is to be executed by the functional unit <<4>>. The instruction replication control word may include a bit mask to indicate that the corresponding functional units of clusters “B”, “C” and “D” are to execute the replicated instructions. In the example of instruction replication control word given hereinabove, the 12-bit mask is 100011001110. Dispatcher 140 will interpret this bit mask as meaning that the machine language instruction in the instruction packet for the functional unit <<1>> of cluster “A” is to be replicated in the functional unit <<1>> of clusters “B”, “C” and “D”, that the machine language instruction in the instruction packet for functional unit <<2>> of cluster “A” is to be replicated in the functional unit <<2>> of clusters “C” and “D”, and that the machine language instruction in the instruction packet for functional unit <<3>> of cluster “A” is to be replicated in the functional unit <<3>> of cluster “D”. The machine language instruction in the instruction packet for functional unit <<4>> of cluster “A” is not to be replicated. The instruction replication feature therefore enables selected machine language instructions to be replicated. The instruction replication feature may also be applied selectively to the different clusters.
The examples given hereinabove illustrate the use of machine language instructions for a “master” cluster, namely cluster “A”, while an instruction replication control word is used to selectively replicate selected ones of those instructions in selected ones of “slave” clusters “B”, “C” and “D”. If the machine language instruction format includes one or more bits to indicate that an instruction is to be executed in cluster “A” or cluster “B”, and the processor has four computational clusters, then another option is to use machine language instructions for two “master” clusters, namely clusters “A” and “B”, while an instruction replication control word is used to selectively replicate instructions for cluster “A” to cluster “C”, and to selectively replicate instructions for cluster “B” to cluster “D”. This latter option may be useful, for example, where each computational cluster includes only one functional unit able to execute a particular type of operation, say shift operations, and a software programmer wants to have two different operations of that particular type in parallel and to replicate each of the different operations of that particular type. It should be noted that if the instructions are to be executed only in the “master” cluster or clusters, then the inclusion of an instruction replication control word in the instruction packet is not needed.
It should be noted that in a processor having only two computational clusters, a short instruction replication control word with enough content bits to include a bit mask of one bit per functional unit in one computational cluster is sufficient to provide full support of the instruction replication feature. In a processor having four computational clusters, a long instruction replication control word with enough content bits to include a bit mask of one bit per functional unit for each of three computational clusters is sufficient to provide full support of the instruction replication feature. In such a processor, a short instruction replication control word as described hereinabove may be used with a control bit to provide one option in which instructions for cluster “A” are replicated to cluster “B” and another option in which instructions for cluster “A” are replicated to all of clusters “B”, “C” and “D”. The short instruction replication control word therefore provides partial support of the instruction replication feature, in that the selectivity of clusters to which a machine language instruction is replicated is limited. In this example, the short instruction replication control word does not have enough content bits to provide support for replication to cluster “C” and/or “D”.
The instruction replication control words described herein may therefore be considered to be scalable with respect to the number of computational clusters and with respect to the number of functional units within each cluster.
Instruction Relocation
Before using the instruction replication feature for SIMD, one or more distinct initialization instructions may need to be executed in the clusters that are to execute the replicated instruction. For example, an initial value may be loaded to an internal register of the functional unit. To enable processor 110 to execute an instruction in a “slave” cluster without executing the instruction in a “master” cluster, an instruction relocation feature may be implemented.
In some embodiments of the invention, the instruction replication control words described hereinabove may be used to support the instruction relocation feature by allocating one or more content bits of the control word to distinguish between replication and relocation control words, and, if appropriate, to identify the replication mode. Similarly, a single mechanism in dispatcher 140 may be used to support both the instruction relocation feature and the instruction replication feature.
The software programmer may write an assembly language program having assembly language instructions that refer to “slave” clusters. The assembler tool will automatically identify the relocated instructions and will generate an instruction packet having the appropriate machine language instructions and an instruction relocation control word. Upon receipt of such an instruction packet, dispatcher 140 will issue the operation of the relocated instruction only to the “slave” cluster.
The machine language instructions refer to the functional units of the master cluster. The assembly language instructions may refer to any of the master cluster and the slave clusters, which are additional clusters in the processor. Through the use of the instruction relocation control word, a machine language instruction that refers to a functional unit of the master cluster are relocated in the processor so that they are executed instead by a corresponding functional unit of one of the slave clusters, in order to accurately implement the assembly language instructions.
For example, the assembly language program may include the following assembly language instruction:
add c0, c1, c2
OR
C.add c0, c1, c2
In this example, the software programmer has indicated that in cluster “C”, the contents of register c0 are to be added to the contents of register c1 and the sum is to be stored in register c2. The assembler tool may determine that cluster “C” is to execute the operation “add” by identifying to which cluster the destination register c2 belongs. Alternatively, the assembly language instruction may explicitly identify that the operation is to be executed by cluster “C”. The assembler tool may therefore use the instruction relocation feature to generate an instruction packet having a single machine language instruction for “add a0, a1, a2” and an instruction relocation control word to indicate that the machine language instruction is to be relocated to cluster “C”. The instruction packet may include additional machine language instructions and control words.
For example, the machine language instruction for “add a0, a1, a2” may include one or more bits that indicate that the “add” operation is to be executed by the functional unit <<1>> of cluster “A”. The instruction relocation control word may include a bit mask to indicate that the corresponding functional unit of cluster “C” is to execute the relocated instruction instead of cluster “A”. If the bit mask of the instruction relocation control word is as given hereinabove in the example of the instruction replication control word, the 12-bit mask is 000010000000. Dispatcher 140 will interpret this bit mask as meaning that the machine language instruction in the instruction packet for the functional unit <<1>> of cluster “A” is to be relocated to the functional unit <<1>> of cluster “C”.
In another example, the assembly language program may include the following assembly language instructions to be executed in parallel:
add a0, a1, a2||not b6, b7||xor c12, c9, c15||sub d0, d6, d4
In this example, the software programmer has indicated that in cluster “A”, the contents of registers a0 and a1 are to be added and the sum is to be stored in register a2. In cluster “B”, the logical NOT of the contents of register b6 is to be stored in register b7. In cluster “C”, the contents of register c12 are to be XORed with the contents of register c9 and the result is to be stored in register c15. In cluster “D”, the contents of register d0 are to be subtracted from the contents of register d6 and the difference is to be stored in register d4.
The assembler tool may identify that there are different assembly language instructions using different indices of the operands in the instruction packet, and that the operands refer to registers of different computational clusters. The assembler tool may therefore use the instruction relocation feature to generate an instruction packet having one single machine language instruction for “add a0, a1, a2”, another single machine language instruction for “not a6, a7”, another single machine language instruction for “xor a12, a9, a15”, another single machine language instruction for “sub a0, a6, a4”, and a control word to indicate that these last three machine language instructions are to be relocated in clusters “B”, “C” and “D”, respectively. The instruction packet may include additional machine language instructions and control words.
For example, the machine language instruction for “add a0, a1, a2” may include one or more bits that indicate that the “add” operation is to be executed by the functional unit <<2>> of cluster “A”, the machine language instruction for “not a6, a7” may include one or more bits that indicate that the “not” operation is to be executed by the functional unit <<3>> of cluster “A”, the machine language instruction for “xor a12, a9, a15” may include one or more bits that indicate that the “xor” operation is to be executed by the functional unit <<4>> of cluster “A”, and the machine language instruction for “sub a0, a6, a4” may include one or more bits that indicate that the “sub” operation is to be executed by the functional unit <<1>> of cluster “A”. The instruction relocation control word may include a bit mask to indicate that the corresponding functional units of clusters “B”, “C” and “D” are to execute the relocated instructions. In the example of instruction relocation control word given hereinabove, the 12-bit mask is 001000011000. Dispatcher 140 will interpret this bit mask as meaning that the machine language instruction in the instruction packet for the functional unit <<3>> of cluster “A” is to be relocated to the functional unit <<3>> of cluster “B”, and the machine language instruction in the instruction packet for functional unit <<4>> of cluster “A” is to be relocated to the functional unit <<4>>0 of cluster “C”, and the machine language instruction in the instruction packet for functional unit <<1>> of cluster “A” is to be relocated to the functional unit <<1>> of cluster “D”.
It should be noted that in a processor having only two computational clusters, a short instruction relocation control word with enough content bits to include a bit mask of one bit per functional unit in a computational cluster is sufficient to provide full support of the instruction relocation feature. In a processor having four computational clusters, a long instruction replication control word with enough content bits to include a bit mask of one bit per functional unit for each of three computational clusters is sufficient to provide full support of the instruction relocation feature. In such a processor, a short instruction relocation control word as described hereinabove may be used to relocate instructions from cluster “A” to cluster “B”. The short instruction relocation control word therefore provides partial support of the instruction relocation feature, in that the selectivity of clusters to which a machine language instruction is relocated is limited. In this example, the short instruction relocation control word does not have enough content bits to provide support for relocation to cluster “C” or “D”.
The instruction relocation control words described herein may therefore be considered to be scalable with respect to the number of computational clusters and the number of functional units in each cluster.
Cross-Accumulator Feature
In a processor having two or more computational clusters, a functional unit of one cluster may want to read a register (or an accumulator) of a different cluster for use as an operand.
The cross-accumulator feature may be supported using a cross-accumulator control word. As with other control words, a cross-accumulator control word includes identification bits and content bits. If, for example, each computation cluster includes four functional units, denoted <<1>>, <<2>>, <<3>> and <<4>>, then the content bits of the cross-accumulator control word may include a 20-bit mask, as follows:
This 20-bit mask includes one bit per computational cluster, and one bit per functional unit for each of the computational clusters. It is obvious to a person of ordinary skill in the art how to modify the cross-accumulator control word for a different number of clusters and/or a different number of functional units per cluster. Moreover, the bits of the bit mask need not be consecutive within the cross-accumulator control word, and the bits of the bit mask may be in any predefined order.
For example, the assembly language program may include the following assembly language instruction:
add b0, a1, a2||abs a13, b7||sub a13, c4, c3||xor c5, d6, d2
The assembler tool may identify that the cross-accumulator feature is being used, and may therefore generate an instruction packet having including:
For example, a short cross-accumulator control word may have content bits including an 8-bit mask, as follows:
The 8-bit mask includes one bit per functional unit for each of two computational clusters. It is obvious to a person of ordinary skill in the art how to modify the short cross-accumulator control word for a different number of computational clusters and/or a different number of functional units per cluster Moreover, the bits of the bit mask need not be consecutive within the short cross-accumulator control word, and the bits of the bit mask may be in any predefined order.
For example, the assembly language program may include the following assembly age instruction:
xor b10, a11, a12||add a11, b7, b2||sub b10, a4, a3||abs a5, a6
The assembler tool may identify that the cross-accumulator feature is being used, and may therefore generate an instruction packet having including:
It should be noted that in a processor having only two computational clusters, a short cross-accumulator control word with enough content bits to include a bit mask of one bit per functional unit in two computational clusters is sufficient to provide full support of the cross-accumulator feature, since cluster “A” can read only from its own accumulator register file and from the accumulator register file of cluster “B”, and cluster “B” can read only from its own accumulator register file and from the accumulator register file of cluster “A”. In a processor having four computational clusters, a short cross-accumulator control word as described hereinabove may be used to provide partial support of the cross-accumulator feature, in that cluster “A” is able to read from the accumulator register file of cluster “B”, but not from that of cluster “D”, and cluster “B” is able to read from the accumulator register file of cluster “A”, but not from that of cluster “C”, and clusters “C” and “D” are able to read only from their own accumulator register files. In such a processor, a long cross-accumulator control word with enough content bits to include a bit mask of one bit per computational cluster and one bit per functional unit for each of four computational clusters is sufficient to provide full support of the cross-accumulator feature.
The cross-accumulator control words described herein may therefore be considered to be scalable with respect to the number of computational clusters and with respect to the number of functional units in each cluster.
Dispatcher 140 then pre-decodes all the entries to identify the instructions and control words, if any (508). Dispatcher 140 then links the extension fields of the control words to the instructions according to the linkage framework, generates cross-accumulator indications, if any, and determines which instructions are replicated or relocated, if any (510). Dispatcher 140 then dispatches the instructions, extensions and cross-accumulator indications to all functional units (512).
While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the spirit of the invention.
