[m-rev.] for review: fix and speed up trie string switches

[Julien Fischer]

On Sat, 30 Mar 2024, Zoltan Somogyi wrote:

> Fix trie string switches, speed them up, ...
> 
> ... and turn them back on.
> 
> compiler/c_util.m:
>     Provide version of output_quoted_string_c which accepts strings

*a* version

>     that may not be well formed, and prints out any code_units that
>     do not belong to a well-formed UTF-8 code point using an octal
>     escape sequence.
>
>     Ask for some predicates with trivial bodies to be inlined.
> 
> compiler/llds_out_data.m:
>     Use the new predicate in c_util to output string constants.
>     This fixes the bug that could cause trie string switches to fail
>     in the presence of strings containing multi-byte code points.
>     In such cases, given the string constants that trie switches can generate,
>     which contain only part of such a multi-byte code unit sequence,
>     llds_out_data.m used to write out a C string constant that contained
>     the unicode replacement character instead of those code units.
> 
> compiler/string_switch.m:
>     It a trie node has four or more code units that can lead to matches, then

s/It/If/

>     use binary search instead of linear search to find out what to do next.
>
>     To make this possible, separate the action of generating such search code
>     from the action of finding out what to do for each possible code unit
>     value.
>
>     Generate comments that can be helpful in tracking down bugs such as
>     the one described above.
> 
> compiler/switch_gen.m:
>     Allow trie string switches once again.
> 
> runtime/mercury_ml_expand_body.h:
>     Add an XXX for new behavior that I found the need for while
>     debugging this change.
> 
> tests/hard_coded/string_switch*.{m,exp}:
>     Add some new alternatives to each swith to create nodes

s/swith/switch/

>     at which the LLDS code generator will now use binary search.
>     Add a query string to test one of these alternatives.
>     (All four test cases are identical, apart from their module names.)
>
>     Expect the changes for the existing keys caused by the new switch arms,
>     as well as the extra outputs for the new query string.

That looks fine otherwise.

Julien.