[Bug c++/70768] Increased compilation time

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70768

--- Comment #3 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
(In reply to James Almer from comment #2)
> (In reply to Markus Trippelsdorf from comment #1)
> > Well, you simply need more RAM to compile this testcase, because gcc-6 uses
> > slightly over 2GB peak, so your machine starts swapping.
> > On my machine (with 8GB RAM) gcc-6 is actually slightly faster.
> > 
> > (For gcc-7 you need to configure it with --enable-checking=release to
> > compare timings.)
> 
> Tried to assign more RAM to the vm and it indeed fixed the trashing and
> slowness with gcc-6 and newer.
> 
> gcc-6/7 uses like 2.1GB of RAM to compile this file whereas gcc-5 uses only
> 1.6GB. Is this intended/expected, or can it be considered a memory hog?

Maybe. gcc-5:

 phase lang. deferred    :  66.28 (84%) usr   2.57 (69%) sys  68.88 (83%) wall
2722388 kB (82%) ggc
 phase opt and generate  :  12.25 (15%) usr   0.92 (25%) sys  13.19 (16%) wall 
469818 kB (14%) ggc
 phase finalize          :   0.00 ( 0%) usr   0.00 ( 0%) sys   0.01 ( 0%) wall 
     0 kB ( 0%) ggc
 |name lookup            :   1.80 ( 2%) usr   0.12 ( 3%) sys   1.99 ( 2%) wall 
279075 kB ( 8%) ggc
 |overload resolution    :  58.89 (74%) usr   2.53 (68%) sys  61.26 (74%) wall
2619094 kB (79%) ggc
 template instantiation  :  60.34 (76%) usr   2.66 (72%) sys  62.90 (76%) wall
2791073 kB (84%) ggc
 TOTAL                 :  79.35             3.72            83.14           
3325932 kB

gcc-6:

 phase lang. deferred    :  74.36 (87%) usr   3.38 (72%) sys  77.73 (86%) wall
3725459 kB (84%) ggc
 phase opt and generate  :  10.30 (12%) usr   1.17 (25%) sys  11.46 (13%) wall 
572078 kB (13%) ggc
 |name lookup            :   2.18 ( 3%) usr   0.27 ( 6%) sys   2.19 ( 2%) wall 
134001 kB ( 3%) ggc
 |overload resolution    :  62.60 (73%) usr   3.25 (69%) sys  66.14 (73%) wall
3543436 kB (80%) ggc
 template instantiation  :  64.42 (75%) usr   3.42 (72%) sys  67.78 (75%) wall
3798026 kB (86%) ggc
 TOTAL                 :  85.52             4.72            90.24           
4424695 kB