RFC: LD: Changing the size of the delta used when growing merge offset maps

[Nick Clifton]

Hi Guys,

  Running the linker under sysprof shows that the append_offsetmap()
  function in merge.c is responsible for a large amount of the memory
  allocated during a link, and a lot of those allocations are calls to
  bfd_realloc().  Since reallocating memory takes time, and represents
  an inefficiency it seems to me that we can do better than having a
  fixed delta for increasing the size of the offset maps.

  So I am proposing the attached patch.  It creates a new static
  variable called map_delta which is used for the array increments.  The
  value of map_delta is selected based upon whether
  --reduce-memory-overheads or -O have been specified on the command
  line.  (I am not sure about the use of the -O flag here, but I could
  not find a more relevant flag to indicate 'this is a big link').

  The results are underwhelming, but still do still make a small amount
  of difference.  For example linking LLVM's ld.llc executable on my
  machine uses 7,121,480 Kb of memory by default and takes around 14.97
  seconds.  But with the patch applied and adding -O to the link command
  line this changes to 7,120,196 Kb and 14.89 seconds.  Not a lot I know
  but maybe a step in the right direction.

  Thoughts / comments ?

Cheers
  Nick

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