Elevated memory usage in def-use

[asl]

We are seeing terrible elevated memory usage in def-use.

We start like this:

    PassRepeated invoking DoSimplifyDefUse
      ProcessDefUse invoking P4::ComputeWriteSet
      heap after P4::ComputeWriteSet: in use 758MB, max 837MB
      ProcessDefUse invoking P4::(anonymous namespace)::FindUninitialized
      heap after P4::(anonymous namespace)::FindUninitialized: in use 758MB, max 837MB

and end like this:

heap after SimplifyDefUse: in use 9.2GB, max 9.3GB

Note that in the reality the heap mem size query triggers GC collection. In the reality the peak memory usage could be well beyond 16 Gb.

I do not know yet the culprit, still investigating.

[asl]

Tagging @ChrisDodd

[asl]

The usual suspect:

Allocated a total of 2.7GB memory
allocated 737MB in 5576175 calls from:
  4   p4c                       0x0000000102ff5234 _ZNK2P411Definitions15joinDefinitionsEPKS0_ + 440 0x102ff5234
...