MidSummer Progress Report

1
Mid-Summer Progress Report

• Darwin Ho
• CAPSL, University of Delaware
• 3rd August 2004

2
Project Outline

• CyclopsE Test Suite (Completed)
• Ported the GCC Test Suite for Cyclops64 to
  CyclopsE.
• Optimize GCC for Cyclops64 (On-going)
• Objective To eliminate unnecessary sign
  extension.

3
Sign Extension Elimination

• Can be eliminated if
• The source operand is already sign-extended.
• Upper 32-bits of its destination operand do not
  affect the correct execution of the succeeding
  instructions.

4
Example 1

• ldw r8, 0(r9)
• addi r8, r8, 1
• shli r8, r8, 32 // (1a)
• shrsi r8, r8, 32 // (1b)
• add r8, r8, r8

• Line 1a 1b can be eliminated as r8 has been
  sign extended after executing the ldw instruction.

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Example 2

• ldw r8, 0(r9)
• ldw r10, 0(r11)
• loop sub r8, r8, r10
• shli r12, r8, 32
• shrsi r12, 12, 32
• shli r13, r10, 32
• shrsi r13, r13, 32
• cmpge r12, r12, r13
• bt r12, loop

• Similarly, the lines in bold can be eliminated as
  r8 and r10 has been sign extended.
• Moreover, as this is a loop, performance can be
  improved by removing the extra code.

6
Approach

• Output from GCC was manually analyzed to find
  code which can be eliminated.
• This was done by drawing a control flow graph of
  the program and comparing the assembly code with
  the original source code (for data dependency).

7
Current Work

• Inserting functions into GCC to build a control
  flow graph and a data dependency table.
• After this has been done, will discuss with Dr.
  Hu to devise an algorithm to eliminate
  unnecessary sign extensions.

8
Summary

• GCC Test Suite for Cyclops64 was ported to
  CyclopsE
• Currently working on optimization of GCC,
  particularly on elimination of unnecessary sign
  extensions.