Explicit Parallel Instruction Computing (EPIC)

• IA-64 ISA

Compared to (VLIW) , no fixed FU expressed in the ISA .

• Explicit parallelism
• Conditional execution of instructions
• Speculative loads
• Large register file

• 3 instructions are combined in one isntruction word called Bundle
• Parallel instructions kept in Groups (delimited by two semicolons)
  • Groups can reach over multiple bundles

• Format of instruction in a bundle:

  

• Conditional execution:

  • instead of jumping, execute both paths and select which one to keep at the end

  

• Shift loads before branches:

  • to prefetch the data
    • if not available (yet maybe) dont raise errors
      • then just fetch it later at the check instruction
    • consecutive writes will check against the prefeched address and invalidate it