[Bug tree-optimization/42172] inefficient bit fields assignments

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42172

--- Comment #10 from amker at gcc dot gnu.org ---
The optimal code is generated on pre-armv7 processors.  The difference starts
from expand.  On armv7-processors, zero_extract operator is generated, rather
than logic operation.  Seem combiner can't handle bit-field in the form of
zero_extract as well as logic forms.

I uploaded ud_dce&combine dumps for both cortex-m0 and cortex-m3.  Apparently,
code for m0 is what we want.