Sharing hard registers

[law@redhat.com]

In message <a05111a12b92efbc4965c@[63.214.71.88]>, Alan Lehotsky writes:
 > At 4:27 PM -0600 6/13/02, law@redhat.com wrote:
 > >In message <200206132203.g5DM3lv24315@potter.sfbay.redhat.com>, 
 > >"Eric Christoph
 > >er" writes:
 > >  > On Thu, 13 Jun 2002 13:27:39 -0700, law wrote:
 > >  >
 > >  >
 > >  > > It may be necessary to back out the last patch which makes gen_rtx_RE
 > G
 > >  > > share hard registers in some circumstances.
 > >  > >
 > 
 > 	The porting guide's "Structure Sharing Assumptions" needs to 
 > be updated to explicitly indicate that hard registers are "shared".
 > Right now, it just says that pseudos are always shared.
Yes.  It's on my list.  It needs to be revised to say that hard regs *may*
be shared.

 > 	Also, I'm curious about the issue of a hard-register with 
 > more than one mode.
 > 	How does that work if R1 can be a SF or a SI mode value???
There's only one mode where the compiler will automatically arrange for a
hard reg to be shared -- that's when you generate one with the same mode
as reg_raw_mode[regno].

 > 
 > 	Doesn't the mode get in the way of sharing the hard register? 
 > Or is this cached by (mode,regno).?
We don't share the full set -- that'd be rather expensive.

jeff