http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54332
--- Comment #18 from dnovillo at google dot com <dnovillo at google dot com> 2012-08-21 18:31:51 UTC --- OK, I think this is the hunk that's causing grief: diff --git a/gcc/df-scan.c b/gcc/df-scan.c index 39f444f..35100d1 100644 --- a/gcc/df-scan.c +++ b/gcc/df-scan.c @@ -4392,7 +4392,6 @@ df_bb_verify (basic_block bb) if (!INSN_P (insn)) continue; df_insn_refs_verify (&collection_rec, bb, insn, true); - df_free_collection_rec (&collection_rec); } /* Do the artificial defs and uses. */ I remember that I ran into this during the VEC conversion (http://gcc.gnu.org/ml/gcc/2012-05/msg00271.html) and after some discussion I ended up convincing myself that taking it out was harmless. Clearly, I was wrong. I've hooked gdb to the running f951 and it's stuck in df_bb_verify(). Odd that this has not triggered anywhere else.