RFA: 4.2 reload infrastructure to fix PR target/21623

[Kaz Kojima]

Joern RENNECKE <joern.rennecke@st.com> wrote:
> Before deciding on how to best install an interim patch for 4.1, I would 
> like
> us to agree on the interface we are going to use for 4.2 - at least 
> inasmuch as
> it would matter for portability of code from the interim patch to the 
> permanent
> solution.

I'm trying to test your patch on my machines.  I've found that a tiny
change is needed for powerpc-apple-darwin7.9.0 because the pcc backend
has its own secondary_reload_class function defined in the rs6000
files.  I've renamed it to rs6000_secondary_reload_class in my test.
It looks that alpha, mn10300, pa and rs6000 define their own
secondary_reload_class.  BTW, I've got a compiler warning during build

../gcc/gcc/reload1.c: In function `emit_reload_insns':
../gcc/gcc/reload1.c:6541: warning: 'letter' might be used uninitialized in this function

and it seems that "letter = *constraint;" is needed just before the line
6552 "new_class = (letter == 'r' ? GENERAL_REGS".

Regards,
	kaz