Hi,
I am currently experimenting with superblock scheduling in a prerelease
version (20040114) of gcc 3.4 on the spec2000 benchmarks. I have
a few questions:
The version that I have does not seem to accept the
-fsched2-use-traces command line switch. So I went a head and set the
following global variables in toplev.c in order to enforce superblock
formation and scheduling:
int flag_optimize = 1;
int flag_schedule_insns = 1;
int flag_schedule_insns_after_reload = 1;
int flag_sched2_use_traces = 1;
Q1. Is there a known bug in version 3.4 related to command-line options?
Or I am doing something wrong?
Q2. Should I set the following flag as well?
int flag_branch_probabilities = ?;
I tried it both ways and the superblocks generated when this flag is
RESET are on average larger and have more branches in them (they are much
harder to schedule), which does not make sense to me. What is superblock
formation based on when branch probablities are not computed? It seems to
me that setting this flag should be necessary!
Q3. Are there any other flags that I need to set in order to ensure
proper superblock formation?
Q3. I have looked into the trace formation code in tracer.c and was
confused about three different terms related to about the same
concept : probability, count and frequency. Is there a documention that
precisely defines each of these three terms and how they are used in
trace formation?
Thanks
-Ghassan
