[m-rev.] for review: reduce the parser's memory consumption

[Julien Fischer]

On Sat, 3 Aug 2019, Julien Fischer wrote:

> On Fri, 2 Aug 2019, Zoltan Somogyi wrote:
>
>>  For tryout and review by Julien. My laptop's timing variability is bigger
>>  than the performance effect of this change; I hope you can measure its
>>  impact
>>  using Opturion's server class machines.
>
> The output from tools/speed_summary is:
>
>     mercury_compile.asm_fast.gc-new average of 6 with ignore=1      8.84
>     mercury_compile.asm_fast.gc-old average of 6 with ignore=1      8.80
>     mercury_compile.hlc.gc-new average of 6 with ignore=1      9.06
>     mercury_compile.hlc.gc-old average of 6 with ignore=1      8.95
>
> (This above are at -O2.)

The diff looks fine.

Julien.