[m-rev.] for review: --inform-ite-instead-of-switch

[Julien Fischer]

On Fri, 23 Nov 2007, Zoltan Somogyi wrote:

> Add a new compiler option. --inform-ite-instead-of-switch. If this is enabled,
> the compiler will generate informational messages about if-then-elses that
> it thinks should be converted to switches for the sake of program reliability.
>
> Act on the output generated by this option.
>
> compiler/simplify.m:
> 	Implement the new option.
>
> 	Fix an old bug that could cause us to generate warnings about code
> 	that was OK in one duplicated copy but not in another (where a switch
> 	arm's code is duplicated due to the case being selected for more than
> 	one cons_id).
>
> compiler/options.m:
> 	Add the new option.
>
> 	Add a way to test for the bug fix in simplify.
>
> doc/user_guide.tex:
> 	Document the new option.

s/tex:/texi:/

>
> NEWS:
> 	Mention the new option.
>
> library/*.m:
> mdbcomp/*.m:
> browser/*.m:
> compiler/*.m:
> deep_profiler/*.m:
> 	Convert if-then-elses to switches at most of the sites suggested by the
> 	new option. At the remaining sites, switching to switches would have
> 	nontrivial downsides. This typically happens with the switched-on type
> 	has many functors, and we treat one or two specially (e.g. cons/2 in
> 	the cons_id type).
>
> 	Perform misc cleanups in the vicinity of the if-then-else to switch
> 	conversions.
>
> 	In a few cases, improve the error messages generated.
>
> compiler/accumulator.m:
> compiler/hlds_goal.m:
> 	(Rename and) move insts for particular kinds of goal from
> 	accumulator.m to hlds_goal.m, to allow them to be used in other
> 	modules. Using these insts allowed us to eliminate some if-then-elses
> 	entirely.
>
> compiler/exprn_aux.m:
> 	Instead of fixing some if-then-elses, delete the predicates containing
> 	them, since they aren't used, and (as pointed out by the new option)
> 	would need considerable other fixing if they were ever needed again.
>
> compiler/lp_rational.m:
> 	Add prefixes to the names of the function symbols on some types,
> 	since without those prefixes, it was hard to figure out what type
> 	the switch corresponding to an old if-then-else was switching on.
>
> tests/invalid/reserve_tag.err_exp:
> 	Expect a new, improved error message.

I've had a quick look through this and can't see anything wrong.
You can go ahead and commit it if you like - I will post any other
review comments I have sometime over the weekend.

Julien.
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