[Bug debug/51746] Segfault in cselib_preserved_value_p

[aoliva at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51746

--- Comment #6 from Alexandre Oliva <aoliva at gcc dot gnu.org> 2012-01-05 
00:58:13 UTC ---
I've now realized the reason we fail to find the (plus:si (reg:si r1)
(const_int -1)) is that reverse_op miscomputes the hash of value 22, because
we're looking up an expr containing a VALUE, and cselib_hash_rtx doesn't handle
that properly.  Getting it to support VALUEs as part of expressions, lookup
succeeds and we reuse the value, as expected.  Here's the patch I'm testing:

diff --git a/gcc/cselib.c b/gcc/cselib.c
index eeb88e6..ab9c458 100644
--- a/gcc/cselib.c
+++ b/gcc/cselib.c
@@ -1035,6 +1035,10 @@ cselib_hash_rtx (rtx x, int create, enum machine_mode
mem

   switch (code)
     {
+    case VALUE:
+      e = CSELIB_VAL_PTR (x);
+      return e->hash;
+
     case MEM:
     case REG:
       e = cselib_lookup (x, GET_MODE (x), create, memmode);