[m-rev.] for review: fix equivalence type performance problems

[Fergus Henderson]

On 17-Dec-2003, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> On 12-Dec-2003, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> > On 12-Dec-2003, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > > compiler/mercury_compile.m:
> > > 	Re-enable equiv_type_hlds.m.
> > > 
> > > tests/hard_coded/Mmakefile:
> > > 	Re-enable testing of equiv_type_hlds.m.
> > 
> > I would like to see some performance figures for how much
> > it costs to run this extra pass before we re-enable it.
> 
> With the extra change below, the equiv_type_hlds pass adds about
> 5% to compile time, much of that in equiv_type.replace_in_type.

The extra changes below are fine.

I'd still rather avoid the extra 5% if we can...
for the --high-level-data grades we can't, but is this pass
really needed for the hlc and LLDS grades?

In fact, it's not just avoiding the extra compilation time;
enabling this pass also weakens our separate compilation guarantees.
For --high-level-data grades, that's undesirable but unavoidable.
For --no-high-level-data grades, I'd like to avoid it if we can.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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