Speculation is an approach that allows the compiler or the processor to "guess" the properties of an instruction, so as to enable execution of other instructions that may depend on the speculated instruction.
Speculation
• Speculation
is an approach that allows the compiler or the processor to "guess"
the properties of an instruction, so as to enable execution of other
instructions that may depend on the speculated instruction. For example, we
might speculate on the result of a branch, so that instructions after the
branch could be executed earlier.
• Need for speculation :
It is the most important methods for finding and exploiting more ILP.
•
Sometimes, speculation may be wrong. Thus it is necessary include a method to
check if the guess was right or wrong and a method to undo the effects of the
instructions that were executed speculatively. The implementation of this undo
capability adds complexity.
•
Compiler can use speculation to reorder instructions.
•
The processor hardware can reorder instructions at runtime.
Review Question
1. What is
speculation?
Computer Organization and Architecture: Chapter 5: Advanced ILP and Parallel Processing : Tag: Computer : Advanced ILP and Parallel Processing - Speculation
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