[Bug tree-optimization/80155] [7/8/9 regression] Performance regression with code hoisting enabled

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80155

--- Comment #44 from Jeffrey A. Law <law at redhat dot com> ---
I'd be very hesitant to make the cost model target specific.  It goes against
core design goals of gimple.

Conceptually I believe we should be optimizing as much as possible on gimple
and that issues such as register pressure should be addressed at the
gimple->rtl border and later, not by throttling the gimple optimizers.

You could potentially look at Cliff Click's work from '95.  It could probably
be repurposed as a general lifetime shrinking pass through statement scheduling
within blocks and across blocks.

You could also look at reviving Bernd's work which tries to do statement
scheduling near the gimple->rtl border.