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From: "luoxhu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/22326] promotions (from float to double) are
 not removed when they should be able to
Date: Mon, 14 Dec 2020 07:21:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D22326

--- 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=E2=80=9D or "fabs(x)+y+z"(x,=
y,z are
float) could result in -+Inf sometimes, while it won't getting float overfl=
ow
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 exces=
sive
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 demot=
ion
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.=