Pointers Extend Unsigned Question

[Jim Wilson]

	The only other target I can think of where this should be a problem
	is a mips3 target running in 64-bit mode with 32-bit pointers.  I
	don't know if anyone actually uses such a configuration in practice.
	I suspect that normally the chip is simply put into 32-bit mode.

The default irix6 ABI (n32) uses 32-bit pointers in 64-bit mode.

The mips backend however always sign extends 4-byte values, regardless of
type, so we shouldn't see this problem for a mips target.  This happens
primarily via TRULY_NOOP_TRUNCATION and the truncate patterns in the md file.

The alpha port doesn't use TRULY_NOOP_TRUNCATION.  It uses different
mechanisms to get a similar effect.  The alpha way is probably better in some
ways.  My recollection though is that the 32-bit alpha port wasn't stable until
after most of the intial irix6 porting work was done, so I ended up using
different methods than what Kenner invented for the 32-bit alpha port.

Jim