Don wrote:
bearophile wrote:
Isn't sin(x)+sin(x) pure? Even if the compiler doesn't want to replace
x+x with x*2 because x is a floating point, it can do:
y = sin(x)
y+y
And that gives the same result even with FPs.
Yes. From further investigation, I've found that:
(1) the optimisation of pure only happens for int returns, not for
floating-point return types. It should convert purefunc(x)+purefunc(x)
into 2*purefunc(x) if the return type of purefunc is int, float, or
complex.
(2) the back-end isn't smart enough to convert f*2 into f+f.
I've fixed (2), patch to the backend is in bigzilla 2888.
I learnt a lot about the backend in the process, maybe I can fix (1) now.
