------- Comment #7 from wilson at gcc dot gnu dot org 2006-01-31 03:49 ------- Things start going wrong in the reload inheritance code. For reload 0, for insn 11, we choose to inherit the value already in r14 in an inner loop in choose_reload_regs. Near the end, we double check to make sure we can still inherit it, and notice we can't because the reload_reg_unavailable test fails. We cancel the inheritance, but we continue to use r14 as the reload reg. We then have to reload the value into r14, possibly hoping that post reload cse can simplify the code. Unfortunately, r14 is used in an auto-inc address in this instruction which gets reloaded, so we have two reloads using the same reg, one of which modifies the reg, and this fails miserably.
The inheritance code is calling find_equiv_reg, and then doing a number of validity tests on the returned result. One of the tests it does is to call regno_clobbered_p. This makes sure the reg isn't used in a clobber or set, but it makes no attempt to look for other kinds of side-effects, such as auto-inc addresses. I think this is where the error lies. If we modify regno_clobberred_p to handle a REG_INC note the same as a clobber, then we would get the right result here for this testcase, as reload 0 is RELOAD_FOR_OPERAND_ADDRESS. I'm not sure if this works in general though. We might need to be more strict for regs used in a REG_INC note, e.g. we might need to disallow them always. I'm curious whether Bernd's new reload-branch works for this testcase. I don't have a post-svn-conversion copy, so I had to check out a new copy and I'm doing a build now. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25603
