https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31313
Kael Franco <kaelfandrew at gmail dot com> changed:
What |Removed |Added
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CC| |kaelfandrew at gmail dot com
--- Comment #3 from Kael Franco <kaelfandrew at gmail dot com> ---
(In reply to Tobias Schlüter from comment #0)
> I just ran into some code which did something like
>
> int strcmp(const char *, const char *);
>
> int f (const char *c)
> {
> return (strcmp (c, "aaa") == 0 || strcmp (c, "aab") == 0);
> }
>
> It would be possible to optimize this into something like (hopefully I get
> it right)
> int f (const char *c)
> {
> if (strncmp (c, "aa", 2))
> return 0;
> return ((c[2] == 'a' || c[2] == 'b') && !c[3]);
> }
>
> Instead, we scan through the whole string twice, as can be seen in the
> assembly.
>
> Likewise, more complicated combinations of comparisons could be reduced into
> an optimal matching sequence. Putting this into component rtl-optimization,
> because the strcmp calls survive all of the tree optimizers unchanged.
This would require implementing Burst trie or suffix tree:
https://stackoverflow.com/questions/10722410/fast-string-comparison-in-c
