Jeff, thanks for picking this up. Jeff Law <l...@redhat.com> writes: > On Thu, 2020-03-12 at 15:26 -0500, Segher Boessenkool wrote: >> On Thu, Mar 12, 2020 at 12:47:04PM -0600, Jeff Law wrote: >> > On Thu, 2020-03-12 at 13:23 -0500, Segher Boessenkool wrote: >> > > > else if (n_sets == 1 >> > > > - && MEM_P (trial) >> > > > + && ! CALL_P (insn) >> > > > + && (MEM_P (trial) || REG_P (trial)) >> > > > && MEM_P (dest) >> > > > && rtx_equal_p (trial, dest) >> > > > && !side_effects_p (dest) >> > > >> > > This adds the !CALL_P (no space btw) condition, why is that? >> > Because n_sets is not valid for CALL_P insns which resulted in a failure on >> > ppc. >> > See find_sets_in_insn which ignores the set on the LHS of a call. So >> > imagine >> > if >> > we had a nop register set in parallel with a (set (reg) (call ...)). We'd >> > end up >> > deleting the entire PARALLEL which is obviously wrong. >> >> Ah, I see. So this is exposed on Power by the TOC stuff, I guess? CSE >> sees a TOC set parallel with a call as a no-op because it is set to the >> same value (an unspec, not an unspec_volatile) that GCC can derive is >> already in the TOC reg? Or is this some other case? > Not entirely sure. Richard's message didn't include the precise details.
Yeah, that was exactly it. On the bright side, removing many calls as dead made for an easy-to-debug bootstrap failure :-) Richard
