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New hazards:
- While Integer/FP split is simple for the HW, get CPI of
0.5 only for programs with exactly 50% FP operations
Data and control hazards cause more stalls:
- Any hazard in an inst
package blocks second issue
Hardware complexity:
- If more inst s issue at same time, greater
difficulty of decode and issue
- Even in 2
, ID must examine 2 opcodes, 6 register specifiers, &
decide if 1 or 2 inst s can issue
(H&P pp.279)
Paul H J Kelly
Mon Dec 1 20:07:28 GMT 1997