Dynamic superscalar

(H&P pp.282)

• Dynamic scheduling should reduce dependence on sophisticated compiler and large no of registers
• Key issue: What hazards can block simultaneous issue?
  • issue dependent inst s together
  • 1.25ex..1.25ex. tags for dependent inst s can be issued to reserv stations concurrently
  • But must check for structural stalls: all reserv stations full, or two inst s need same one
  • Issue is in-order: if inst of an n-word package has an issue stall, it's very hard to issue inst -inst
  • (n completions/clock needs n CDBs)
• Nasty problem:
  • Conditional branches