http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52684
--- Comment #4 from davem at gcc dot gnu.org 2012-05-01 22:44:08 UTC --- Ok, I see why 32-bit works. On 32-bit we use real libfuncs in the optabs, so the compiler can see all the typing information and emit the proper information to stick into the CALL_INSN_FUNCTION_USAGE lists. But when we emit soft TFmode libcalls by hand, as on 64-bit, this information is lost. So DSE has nothing to work with and can't see that the temporary stack slots are inputs to the libcall. We'll have to tack on our own reg use notes by hand in functions like emit_soft_tfmode_libcall() and sparc_emit_float_lib_cmp().
