Open64: A Framework for High performance Compiler

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Open64 A Framework for High performance Compiler
March 2007
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Outline

• Open64 History
• Osprey Project
• Research Activities
• Retargetability

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Open64 Based Research Activites at University of
Delaware

• Open64 Code Porting for Large-Scale Multi-Core
  Architectures
• Code Optimization for Large-Scale Multi-Core
  Architectures
• Research on a point-to alias analysis under a SSA
  framework
• Landing Software Pipelining on Large-Scale
  Multi-Core Architectures

4
Port Open64 to Cyclops64
based on Pathscale 2.2.1/x8664
Begin with gcc 3.2.1/MIPS C FE, we change the MD
so that it can generate AST compatible with
cyclops64s ABI
Rewrite from scratch for C64
Only dep-test are enabled, the loop
transformation are not enabled because org loop
transformation is not readily applicable for arch
without cache
Changed heavily CGIR lowering, scheduling, EBO
etc
tools chains (as, ld, simulator etc) are provided
by ETI.
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Some researches on Open64/C64

• Scratch pad utilization
• Divide scratch pad memory into 3 areas 2nd level
  general purpose register (L2 GPR) , software
  rotating register (SRR), free area
• L2 GPR further divide into caller/callee-save,
  color live ranges with L2 GPR when RA run out of
  real registers.
• SRR prefetching, improve temporal locality
• E.g1 prefech 5 iterations ahead for () x
  gt for () rrx x rrx5
• E.g2 improve temporal locality for (i0 i
  lt10000 i ai bi ai-5 gt for
  (i0 i lt10000 i rrx bi rrx-5
  airrx
• Use LDM (load multiple word) to reduce bandwidth
  bandwidth requirement

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Unification based points-to analysis using SSA

• Motivations
• Incremental change to existing Steensgaards PT
  analysis with better precision
• Retain almost linear time
• Limited flow sensitivity improve the precision
  of analysis of p and q where p and q are global
  variable/pointer, or it may be modified by
  callees.
• Reduce the imprecision due to unification
• Limited Flow sensitivity by SSA form
• build (preliminary) SSA form for all variables
  (inc global variables and local var with address
  taken). Do not take into account the alias.
• Perform Points-to on the preliminary SSA form,
  update the SSA form during PT analysis p3
  initially points-to n, after analyzing stmt 4,
  p3points to both n and z

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Unification based points-to analysis using SSA
(cont)

• Differentiate flat unification and updating
  unification
• Flat unification let s1points_to(p1),
  s2points_to(p2), statements p cond ? p1 p2
  make s1 and s2 unified simply because p may
  points to both set. The s1 and s2 themselves
  dont need updated at the moment unification
  happens.
• Incremental update points_to(p1) gt a, b, q1
  some_ptr, may change ps value, hence
  points_to(p1) should be updated into a,b U
  points_to(some_ptr).
• The final unified set encode the type of
  unification of smaller subset. Flat-unified
  sub-sets are still disjointed.

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Software Pipelining of Multi-Core Architectures
A Brief Introduction

• Problem description
• Software toolchain
• Where Open64 helped
• Some results.

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Problem Description

• Software-pipelining on multi-threaded
  architectures
• Single-dimension Software-Pipelining (SSP)
• Workload distribution
• Data communication
• Data synchronization

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Software Pipelining Toolchain Based on Open64
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Implementation
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What Open64 features are used in multi-core
software pipelining

• Multi-dimensional dependence analysis
• WHIRL clean interface
• Machine model
• Reservation tables
• Register allocation
• Modulo-scheduler
• Code generator
• No need to implement everything to test
• Clean code despite lack of documentation!

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Cyclops64 architecture
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Some Results