While implementing some code I have seen that LDC (that uses Tango) isn't able
to inline the code of expi, that is little more than a fsincos asm instruction.
LDC is now able to inline sqrt, etc (that increases their efficiency a lot),
but expi contains asm, and such functions aren't allowed to be inlined.
LDC has a way to allow such inlining of asm-containing functions anyway:
pragma(allow_inline)
So I have seen my code get faster (with LDC) when I have used the following
expi instead of the Tango one (I have removed the part that manages the case of
no asm allowed because I was doing a quick test):
creal expi(real y) {
version (LDC) pragma(allow_inline);
asm {
fld y;
fsincos;
fxch ST(1), ST(0);
}
// add code here if asm isn't allowed
}
Instead of just adding "version (LDC) pragma(allow_inline);" at the top of some
Tango functions (array operations too can enjoy such inlining, because if you
do a[]+b[] and their length is 4 there is a big overhead to call tango/Phobos
functions), isn't it better to add to the D language something standard (= that
works on DMD too) to state that some asm function can be inlined?
(Generally the idea of porting back tiny things from LDC to DMD sounds nice,
especially when DMD back-end is able to support them).
Bye,
bearophile
