[Bug tree-optimization/22326] promotions (from float to double) are not removed when they should be able to

[luoxhu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22326

--- Comment #22 from luoxhu at gcc dot gnu.org ---
https://gcc.gnu.org/pipermail/gcc/2020-December/234474.html

So this issue seems invalid since "fabs(x)*y+z” or "fabs(x)+y+z"(x,y,z are
float) could result in -+Inf sometimes, while it won't getting float overflow
under double computation.  Float value range info is required here.



Quoto Richard's reply:

I still think that covering all "good" cases in match.pd will require excessive
matching and that it is better done in a pass (this would include removing
the frontend handling for math functions).  Note that for example
(float)((double)x + (double)y) with float x and y is also eligible to demotion
to float, likewise may some compositions like
(float)(sin((double)x)*cos ((double)y))
for float x and y since we can constrain ranges here.  Likewise
(float)((double)x + fabs ((double)y)) for float x and y.  The
propagation would need
to stop when the range needed increases in unknown ways.