[Bug c++/55442] G++ uses up all my RAM when compiling a constexpr with exponential call graph

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55442

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Thu Jun 27 21:29:19 2019
New Revision: 272765

URL: https://gcc.gnu.org/viewcvs?rev=272765&root=gcc&view=rev
Log:
        PR c++/55442 - memory-hog with highly recursive constexpr.

This testcase in the PR is extremely recursive, and therefore uses a huge
amount of memory on caching the results of individual calls.  We no longer
need to track all calls to catch infinite recursion, as we have other limits
on maximum depth and operations count.  So let's only cache a few calls at
the top level: 8 seems to be a reasonable compromise.

gcc/c-family/
        * c.opt (fconstexpr-loop-limit): New.
gcc/cp/
        * constexpr.c (push_cx_call_context): Return depth.
        (cxx_eval_call_expression): Don't cache past constexpr_cache_depth.

Modified:
    trunk/gcc/c-family/ChangeLog
    trunk/gcc/c-family/c.opt
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/constexpr.c
    trunk/gcc/doc/invoke.texi