Re: [Emacs-diffs] feature/byte-switch 7c2d493: src/bytecode.c: Add optional sanity check for jump tables.

Re: [Emacs-diffs] feature/byte-switch 7c2d493: src/bytecode.c: Add optional sanity check for jump tables.

[Stefan Monnier]

> +            /* Hash tables for switch are declared with :size set to the
> +               exact number of cases.  */
> +            if (BYTE_CODE_SAFE)
> +              eassert (HASH_TABLE_SIZE (h) == h->count);

Why should we force this constraint on the code that generates the
hash-tables.  I think this is wrong.  We just need a comment that
explains that we use h->count as a faster approximation of
HASH_TABLE_SIZE(h) (and BTW, the comment belongs next to the relevant
code which is not the `for` loop but the "if (h->count <= 5)" test) and
that we hence leave it to the bytecompiler to ensure that this
approximation is good enough.


        Stefan

Re: [Emacs-diffs] feature/byte-switch 7c2d493: src/bytecode.c: Add optional sanity check for jump tables.

[Vibhav Pant]

On Sat, Feb 11, 2017 at 9:21 PM, Stefan Monnier
<monnier@iro.umontreal.ca> wrote:
>> +            /* Hash tables for switch are declared with :size set to the
>> +               exact number of cases.  */
>> +            if (BYTE_CODE_SAFE)
>> +              eassert (HASH_TABLE_SIZE (h) == h->count);
>
> Why should we force this constraint on the code that generates the
> hash-tables.  I think this is wrong.

Also, the rationale for putting a constraint on the :size of the hash
table was that it would save pure storage if the function (and thus
the jump table in the constant vector) was purecopied.

-- 
Vibhav Pant
vibhavp@gmail.com

Re: [Emacs-diffs] feature/byte-switch 7c2d493: src/bytecode.c: Add optional sanity check for jump tables.

[Stefan Monnier]

> Also, the rationale for putting a constraint on the :size of the hash
> table was that it would save pure storage if the function (and thus
> the jump table in the constant vector) was purecopied.

But that's also a mere optimisation.  Not something whose absence
deserves an abort.


        Stefan