[Bug c++/66584] gcc differs in static, branch-prediction cost from icc in switch.

["jmcguiness at liquidcapital dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66584

Jason McG <jmcguiness at liquidcapital dot com> changed:

           What    |Removed                     |Added
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             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |---

--- Comment #5 from Jason McG <jmcguiness at liquidcapital dot com> ---
(In reply to Andrew Pinski from comment #3)
> More than that, documenting gcc's branch heuristics is just in the code. And
...

I am sorry, but I do not agree. As per my other reply, in comment 4, I think it
is entirely reasonable to request that an additional statement along the lines
of "code generation for switch statements may not follow a top-down approach
nor prefer the default case (if it exists) in terms of static
branch-prediction. The __builtin_expected() intrinsic has no effect" is
included in the web-based documentation in a suitable sub-section. If some
algorithm were used, then adding a link to the web site to the appropriate
paper might be a quick remedy?

This would ensure that developers are not mislead by the argument that
__builtin_expected() takes thinking they could use that, nor would they be
mislead by lore assuming that the default or a lexographic top-down approach to
static branch-prediction were used.