https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38939
Segher Boessenkool <segher at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2015-11-23
CC| |segher at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #2 from Segher Boessenkool <segher at gcc dot gnu.org> ---
The problem is that expand_mult (in expmed.c) calculates the cost of
the reg*0x01010101 as six cycles, namely, two to construct the constant
in a register and then four for the reg-reg multiply. The shift
sequence is just four cycles, so that is chosen. expand_mult does not
realise this is within a loop and the construction of the constant will
be hoisted out of the loop.
Confirmed.
