On 11/24/2016 03:36 PM, Segher Boessenkool wrote:
On Thu, Nov 24, 2016 at 03:26:45PM +0100, Bernd Schmidt wrote:
On 11/24/2016 03:21 PM, Segher Boessenkool wrote:
Combine uses insn_rtx_cost extensively. I have tried to change it to use
the full rtx cost, not just the source cost, a few times before, and it
always only regressed. Part of it is that most ports' cost calculations
are, erm, not so great -- every target we care about needs fixes.
Let's please not try this in stage 3.
It got approved and committed. Do you want me to revert it now or wait
for obvious signs of fallout?
In my opinion it is an early stage 1 thing, not something suitable for
stage 3. I can do some simple tests on various targets if you want.
Sure.
I'll make the argument that stage 3 is when we fix stuff, including
performance regressions, and this patch is very clearly a fix. When we
have very obvious distortions like a case where costs from insn_rtx_cost
and seq_cost aren't comparable, it's impossible to arrive at sane solutions.
Bernd
