On Sunday, 12 August 2018 at 02:17:21 UTC, Cecil Ward wrote:
On Sunday, 12 August 2018 at 00:55:50 UTC, Paul Backus wrote:
On Sunday, 12 August 2018 at 00:15:37 UTC, Cecil Ward wrote:
Paul, what would the calls look like?
I am about to misunderstand things completely so here goes :-)
It would be a bit kludgy having to switch from one calling
syntax to another, putting the mask argument in the template
parameters or in the normal position. Or have I
misunderstood? And if the caller did not use the right call
syntax variant then the optimisation would not happen. Thing
is, as it is the details are nicely hidden and the caller
does not even need to thing about the fact that an
(eponymous) template is being used.
As far as I know, there's no way to *guarantee* the
optimization and keep the normal function call syntax.
Probably the best you can do is write the mask check as a
regular if statement, put `pragma(inline, true)` in the
function, and hope the optimizer is smart enough to get rid of
the branch.
I was thinking about reflection and powerful things like
traits. Would a test to see if a static if compile do the trick
? You ask the question using traits : "does the following
compile? : { static if ( mask == 3 ) { }; }" - any use?
I am out of my depth but I am also wondering about using mixin in
some way, conditionally.
And the kind of thing I am also thinking about is something like
if this ( xxx ) compiles then xxx // put in the code under a
conditional compilation if
else pull in alternative code
and all the ifs are compile time. so zero run time penalty which
absolutely essential in my case because in fact the bodies are
just single instructions and it is a choice between a cheaper
instruction ( or no instruction at all ) and a 3-4 times more
costly instruction, but an if statement is 50 times more
expensive because of branch misprediction risk as well as the
cost of the test itself
