Program instruction fusion
A data processing system includes an instruction pipeline containing instruction queue circuitry, fusion circuitry and decoder circuitry. The fusion circuitry serves to identify fusible groups of program instructions within a Y-wide window of program instructions and supply a stream of program instructions including such replacement fused program instructions to a X-wide decoder circuitry which decodes X program instructions in parallel using parallel decoders.
1. Apparatus for processing data comprising:
instruction queue circuitry to queue pre-fusion program instructions to be executed;
fusion circuitry to receive said pre-fusion program instructions from said instruction queue circuitry and to identify and replace fusible groups within said pre-fusion program instructions with respective fused program instructions to form post-fusion program instructions; and
decoder circuitry to receive said post-fusion program instructions from said fusion circuitry and to decode said post-fusion program instructions; wherein
said decoder circuitry is configured to decode in parallel up to X of said post-fusion program instructions, where X is an integer greater than one; and
said fusion circuitry is configured to wait until a window of Y pre-fusion program instructions is received and, in response to receiving the window of Y pre-fusion program instructions, to identify said fusible groups within the window of Y pre-fusion program instructions, where Y is a predetermined integer greater than X.
2. Apparatus as claimed in claim 1 , wherein said window of Y pre-fusion program instructions comprises Y adjacent program instructions within an ordered stream of program instructions to be executed.
3. Apparatus as claimed in claim 1 , wherein said instruction queue circuitry, said fusion circuitry and said decoder circuitry comprise respective portions of instruction processing pipeline circuitry.
4. Apparatus as claimed in claim 1 , wherein said fusion circuitry and a first portion of said decoder circuitry comprise a pipeline stage of said instruction processing pipeline circuitry.
5. Apparatus as claimed in claim 3 , wherein said instruction queue circuitry comprises a buffer to store a plurality of said pre-fusion program instructions and to receive one or more pre-fusion program instruction from instruction prefetch circuitry and to output one or more pre-fusion program instructions to said fusion circuitry within a single clock cycle of said instruction processing pipeline circuitry.
6. Apparatus as claimed in claim 1 , wherein said fusion circuitry identifies a fusible group using one or more characteristics of said pre-fusion program instructions, said one or more characteristics comprises that a first pre-fusion program instruction within said fusible group has an output operand that serves as an input operand to a second pre-fusion program instruction within said fusible group.
7. Apparatus as claimed in claim 1 , wherein said fusible groups comprise two adjacent pre-fusion program instructions within a stream of pre-fusion program instructions.
8. Apparatus as claimed in claim 1 , wherein Y=X+1.
9. Apparatus as claimed in claim 1 , wherein X=3.
10. Apparatus for processing data comprising:
means for queuing pre-fusion program instructions to be executed;
means for receiving said pre-fusion program instructions from said means for queuing pre-fusion program instructions and for identifying and replacing fusible groups within said pre-fusion program instructions with respective fused program instructions to form post-fusion program instructions; and
means to receive said post-fusion program instructions from said means for receiving said pre-fusion program instructions and to decode said post-fusion program instructions; wherein
said means for receiving said post-fusion program instructions is configured to decode in parallel up to X of said post-fusion program instructions, where X is an integer greater than one; and
said means for receiving said pre-fusion program instructions is configured to wait until a window of Y pre-fusion program instructions is received and, in response to receiving the window of Y pre-fusion program instructions, to identify said fusible groups within the window of Y pre-fusion program instructions, where Y is a predetermined integer greater than X.
11. A method of processing data comprising:
queuing pre-fusion program instructions to be executed within instruction queue circuitry;
using fusion circuitry to receive said pre-fusion program instructions from said instruction queue circuitry and to identify and replace fusible groups within said pre-fusion program instructions with respective fused program instructions to form post-fusion program instructions; and
using decoder circuitry to receive said post-fusion program instructions from said fusion circuitry and to decode said post-fusion program instructions; wherein
said decoder circuitry decodes in parallel up to X of said post-fusion program instructions, where X is an integer greater than one; and
said fusion circuitry waits until a window of Y pre-fusion program instructions is received and, in response to receiving the window of Y pre-fusion program instructions, identifies said fusible groups within the window of Y pre-fusion program instructions, where Y is a predetermined integer greater than X.