On 2014-05-13, 6:27 AM, Kyrill Tkachov wrote:
Hi all,
In haifa-sched.c (in rank_for_schedule) I notice that live range
shrinkage is not performed when SCHED_PRESSURE_MODEL is used and the
comment mentions that it results in much worse code.
Could anyone elaborate on this? Was it just empirically noticed on x86_64?
It was empirically noticed on SPEC2000. The practice is a single
criteria for heuristic optimizations. Sometimes a new heuristic
optimization might look promising but the reality might be quite different.
In this relation I am remembering a story told me by Bob Morgan about
bin packing RA invention. It was just a quick and simple first RA
implementation for a new compiler. After that DEC compiler team tried
many times to improve the RA implementing more complicated optimizations
but the first bin packing RA was always better.
