Need advice on bounds checking approaches

[Jeffrey A Law]

  In message < msaejkt998.fsf@gkm-dsl-194.ascend.com >you write:
  > > 
  > > I'd be much happier if we could find a clean way to get the optimizations
  > > you need using our existing optimizers.
  > 
  > We can do without a special pass.  CSE seems the best place to
  > eliminate redundant checks, so we'd just need a little bit of code to
  > handle the new check_bounds_rtx.  We can just forget about doing
  > default translation of check_bounds_rtx into primitive RTL, and
  > require that targets supporting bounds checking handle it in the
  > machine description.  So far, all of the targets I want to support
  > initially (i960, PowerPC, i386, MIPS) will benefit from special
  > handling in the MD file anyway.
  > 
  > Does that sound reasonable?
Seems reasonable.  We should probably have some way to automatically warn the
user if they try to use bounded pointers on a target which does not have 
conditional traps, etc.

We could probably note if the target supports conditional traps during one
of the RTL initializers and warn when we encounter a [un]bounded keyword or
attribute during parsing.

jeff