Add a flag that forces cold blocks to be evicted from a loop. NFC.
needs a test case, and needs an adjustment to the frequency for non-profile functions.
FWIW, I see a 10% performance improvement on one of our internal benchmarks with this patch + force-precise-rotation-cost, compared to force-precise-rotation-cost alone.
I wrote a testcase that covers this flag in https://reviews.llvm.org/D36338
Submitted in r310129