[Bug tree-optimization/30089] Compiling FreeFem3d uses unreasonable amount of time and memory

["dnovillo at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #9 from dnovillo at gcc dot gnu dot org  2006-12-13 23:50 -------

The memory problem is quite simple: We just have a *lot* of pointers and a
*lot* of addressable symbols.  Here is a breakdown of what happens on the first
call to compute_may_aliases:

During the first call to compute_may_aliases:

1- Size of cc1plus is 339Mb
2- Call to compute_points_to_sets grows to 355Mb (+4.72%)
3- Call to compute_flow_insensitive_aliasing grows to 364Mb (+2.54%)
4- Call to compute_flow_sensitive_aliasing grows to 667Mb (+83.2%)

The reason for this tremendous growth is quite simple.  There are 39,010 SSA
name pointers and many of them have their own points-to set, which we store in
that name's may-alias set.  We grow to 667Mb in the last loop of
compute_flow_sensitive_aliasing.

One thing we could do is just not use flow-sensitive information in these
cases.  If we don't set SSA_NAME_PTR_INFO, everything will default to
flow-insensitive information and things will Just Work.

Perhaps using sparse bitmaps for the may-alias sets might help with memory
consumption, but I found these bitmaps to slow down the operand scanner quite a
bit in the past.  May be worth a try.

Danny, thoughts?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30089