Painful problems with -fpic implementation on powerpc-sysv

[Jeffrey A Law]

  In message < 9808232356.AA36800@marc.watson.ibm.com >you write:
  > >>>>> Geoff Keating writes:
  > 
  > Geoff> Reload sees that its choices are either:
  > 
  > Geoff> - load immediate value in GPRs, store value to memory, load FPR back
  > Geoff> from memory;  or
  > Geoff> - load FPR directly from memory.
  > 
  > Geoff> Naturally, it chooses the second.
  > 
  > 	That is exactly my point.  reload has another alternative and is
  > *choosing* the load from memory based upon some cost analysis.  I propose
  > changing the cost analysis when in reload so that the value is
  > materialized in GPRs and transferred via stack memory instead of a
  > symbol_ref. 
Generally that does not work -- it's just a cost, and eventually the
costs will do something unexpected and you'll lose.  One of my all-time
losers was when I had a cost thing in reload overflow and reload
thought using the 5bit shift register on the PA was really cheap
instead of really expensive (and wrong if you've got a 32bit value).

I would not recommend this approach.


jeff