[Bug target/42040] [ia64] Inappropriate address spills

["wilson at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #5 from wilson at codesourcery dot com  2010-03-13 08:23 -------
Subject: Re:  [ia64] Inappropriate address spills

On third thought...
The code here makes sense if we were having problems with invalid
constant recombinations.  symbol+const gets split by ia64_expand_move
into symbol+highpart which is put in the got, and lowpart which is added
with adds.  If a late optimization pass saw a REG_EQUAL note and tried
to put the constant back together again, that would be inconvenient.
The ia64_legitimate_constant_p code would prevent that.  Unfortunately,
this code also prevents us to accepting a constant before
ia64_expand_move is called, which prevents us from splitting it in the
first place.  This looks to be more complicated than I hoped.

There is a variable we can check to see if we are in the expand phase,
currently_expanding_to_rtl.  Perhaps we need to accept any constant if
currently_expanding_to_rtl is true, and only accept symbol+highpart (the
current code) if it is false.  Or alternatively, if this problem only
happened at reload time, then checking reload_in_progress and/or
reload_completed might work.

I will have to look at PR28490 again and try to remember what the
original problem that we were fixing was.

Jim


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42040