[tree-ssa] 20% compile time regression vs. 3.4

[Per Bothner]

Richard Guenther wrote:

> I thought it was time for another 3.4 vs. tree-ssa compile-time
> comparison.  For -O2 compile-time we regressed quite a bit (20%) with the
> main problem areas are (first 3.4, second tree-ssa):
> 
>  garbage collection    :  12.19 ( 7%) usr   0.00 ( 0%) sys  12.50 ( 7%) wall
>  garbage collection    :  17.26 ( 8%) usr   0.02 ( 0%) sys  17.45 ( 8%) wall
> 
> tree-ssa uses about double amount of memory

Tree-ssa expression nodes point to a separately-allocated location_t
object.  It does try to share these, but it will to extra gc time, if
nothing else.

I could try to dust off my "replace location_t by source_location"
patch.  I don't know if it would be appropriate for the current stage
of tree-ssa "semi-freeze", though it helps with compile speed (no
guarantee that it does), maybe I should try it.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/