Millicode calls, GP register, ld -r

[John David Anglin]

> Alan Modra <alan@linuxcare.com.au> writes:
> 
> > I'll install a slightly modified version of your patch.  The other PLABEL
> > relocs should be handled as for PLABEL32, not that it matters for gcc
> > output as I've never caught gcc generating code that used PLABEL14R and
> > PLABEL21L.  A pity, because current gcc PIC code for handling function
> > pointers is rather inefficient.  Typically, you get something like:
> > 
> > .LC1:
> >         .word P'bar
> > .
> > .
> >         addil LT'.LC1,%r19
> >         ldw RT'.LC1(%r1),%r22
> >         ldw 0(%r22),%r22
> > 
> > which could all be replaced with
> > 
> > 	ldil LP'bar,%r22
> > 	ldo RP'bar(%r22),%r22
> > 
> > saving on code size, memory accesses, and relocs.
> 
> Interesting.  It would be trivial to hack that into GCC, I just wonder
> if there's some good reason it hasn't been done before.

The HP linker `-O' option eliminates unnecessary ADDIL instructions and
dead procedures.  Probably, it wasn't deemed necessary.  However, not
many remember to include -Wl,-O in their link flags.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6605)