On 03/26/2012 07:37 PM, Eric Botcazou wrote: >> Does 4.7 still have the failure at all? I've checked with the 4.6 >> branch, and regrename gets confused because there's a REG_DEAD note for >> the register, and another REG_UNUSED for the same reg. As far as I >> remember, it used to be the case that there should not be a REG_DEAD >> note for a register that gets set in the insn, but maybe df changed the >> rules? Or maybe it was a df bug in 4.6? > > My understanding is that the REG_UNUSED note causes the chain opened for a > dest > register operand to be immediately closed but, when you have multiple such > dest register operands, one would need to have the chain live "during the > instruction" or right after, so that you have a conflict with the other dest > register operands for the instruction. This looks awkward though.
You're right on the behaviour of REG_UNUSED, but it only takes effect after all destinations have been opened. So they still conflict with each other, usually. Here, I think the problem is that we have an in-out operand whose chain is closed prematurely due to a bogus REG_DEAD note which shouldn't be there for a register set in the instruction. Bernd
