Branch unconditional no save pc pcimm branch absolute

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Branch (unconditional, no save PC, PC+imm) Branch absolute (uncond, no save PC, imm) Branch and link (uncond, save PC, PC+imm) Branch abs and link (uncond, save PC, imm) Branch conditional (conditional, no save PC, PC+imm) Branch cond abs (cond, no save PC, imm) Branch cond and link (cond, save PC, PC+imm) Branch cond abs and link (cond, save PC, imm) Branch cond to link register (cond, don’t save PC, reg) Branch cond to link reg and link (cond, save PC, reg) Branch cond to count reg (cond, don’t save PC, reg) Branch cond to count reg and link (cond, save PC, reg)
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Branches – DEC Alpha 1. Alpha 3 Types of Branches Conditional branch (cond, no save PC, PC+imm) Bxx Ra, disp Unconditional branch (uncond, Save PC, PC+imm) Br Ra, disp Jumps (uncond, save PC, Register) J Ra
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Branches – MIPS 1. MIPS 6 Types of Branches Jump (uncond, no save PC, imm) Jump and link (uncond, save PC, imm) Jump register (uncond, no save PC, register) Jump and link register (uncond, save PC, register) Branch (conditional, no save PC, PC+imm) Branch and link (conditional, save PC, PC+imm)
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What’s So Bad About Branches? Effects of Branches Fragmentation of I-Cache lines Need to determine branch direction Need to determine branch target Use up execution resources Pipeline drain/fill
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What’s So Bad About Branches? Problem: Fetch stalls until direction is determined Solutions: Minimize delay Move instructions determining branch condition away from branch (CC architecture) Make use of delay Non-speculative: Fill delay slots with useful safe instructions Execute both paths (eager execution) Speculative: Predict branch direction
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What’s So Bad About Branches?
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  • Fall '09
  • PROFGURISOHI
  • Central processing unit, CPU cache, Branch predictor, branch, Instruction Flow, addi addi addi

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