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CM3 / RVDS / NOPs

David Clark
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  • Note: This was originally posted on 15th June 2010 at http://forums.arm.com

    I guess the loop structure:
      do { __disable_irq(); } while (0)
    might have cause the NOPs.
    Although it didn't expand into a loop, the compiler might have reserved the space for instructions if a loop is needed.
    And because it is -O0, it didn't remove the unused instruction space and hence NOPs is used.


    Hi Joseph,

    Thanks for the reply.  Yeah, I guess the [font="Courier New"]do {} while()[/font] construct caused the NOPs, since that is the noticeable difference in the source, but even then, their presence is puzzling.  I suppose I could try putting something other than PRIMASK manipulation in the statement, something like incrementing a counter or whatever, and seeing if the NOPs are still generated, but for now it's "case closed".

    Maybe the -O1 optimization level should be my baseline level -- seems like there is probably still good debugging visibility.

    Again, many thanks for the time & replies.
Reply
  • Note: This was originally posted on 15th June 2010 at http://forums.arm.com

    I guess the loop structure:
      do { __disable_irq(); } while (0)
    might have cause the NOPs.
    Although it didn't expand into a loop, the compiler might have reserved the space for instructions if a loop is needed.
    And because it is -O0, it didn't remove the unused instruction space and hence NOPs is used.


    Hi Joseph,

    Thanks for the reply.  Yeah, I guess the [font="Courier New"]do {} while()[/font] construct caused the NOPs, since that is the noticeable difference in the source, but even then, their presence is puzzling.  I suppose I could try putting something other than PRIMASK manipulation in the statement, something like incrementing a counter or whatever, and seeing if the NOPs are still generated, but for now it's "case closed".

    Maybe the -O1 optimization level should be my baseline level -- seems like there is probably still good debugging visibility.

    Again, many thanks for the time & replies.
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