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SIMD Masking

• Two ways to be disabled for c=a+b;
  • if (!disabled) c=a+b;
  • c=(((a+b) & -!disabled)|(c & ~-!disabled));
• How to track enable nesting?
  • Use an enable stack
  • Count disable nesting depth [Keryell & Paris]
• What happens if no PE is enabled?
  • Execute code anyway (C*)
  • Jump over code (MPL)