On 10/21/2015 02:56 AM, Richard Biener wrote:
On Mon, Oct 19, 2015 at 6:23 PM, Jeff Law <l...@redhat.com> wrote:
If I hack up GCC's old jump threader to avoid threading across backedges and
instead let the FSM threader handle that case, then we end up with cases
where the FSM threader creates irreducible loops with marginal benefit.
This can be seen in ssa-dom-thread-2{d,e,f}.c.
We've long avoided such threads in the old jump threader. We generally want
to avoid them in the FSM threader as well. The only case where we're going
to allow them is when we're able to eliminate a multi-way branch from the
loop.
Bootstrapped and regression tested on x86_64-linux-gnu. Also tested the
above mentioned testcases with my hacked up compiler.
Installed on the trunk.
Note that this fixed some of the size regressions I see on SPEC CPU 2000
but not all, esp. 176.gcc seems to be as bad as before (seen with plain -O2
on x86_64).
I haven't started looking at them explicitly yet. Good to know it
helped some though.
jeff
