https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85755
Segher Boessenkool <segher at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2018-05-12
Ever confirmed|0 |1
--- Comment #1 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Before RA it is all just fine:
insn_cost 4 for 14: [++r121:DI]=r122:DI
REG_INC r121:DI
insn_cost 4 for 15: r122:DI=r122:DI+0x1
insn_cost 0 for 30: {pc={(r129:DI!=0x1)?L16:pc};r129:DI=r129:DI-0x1;clobber
scratch;clobber scratch;}
REG_BR_PROB 955630228
IRA make a good choice:
Disposition:
3:r121 l0 3 0:r122 l0 9 4:r125 l0 3 2:r126 l0 4
5:r127 l0 68 1:r129 l0 66
and then LRA comes along:
Choosing alt 6 in insn 14: (0) ^m (1) d {*movdi_internal64}
Creating newreg=132 from oldreg=122, assigning class FLOAT_REGS to r132
14: [++r121:DI]=r132:DI
REG_INC r121:DI
Inserting insn reload before:
35: r132:DI=r122:DI
We want to have alt 0 instead (r -> YZ), which gives
0 Non input pseudo reload: reject++
alt=0,overall=7,losers=1,rld_nregs=0
but we get alt 6 (d -> ^m), which gives
alt=6,overall=6,losers=1,rld_nregs=1
Putting the disparagement on the correct operand, i.e. as ^d -> m gives
alt=6,overall=12,losers=1 -- refuse
and we should make that change; but yes we want an stdu, too. Should "Y"
allow that?
GCC 7 did this fine; GCC 8 of a month ago, too. What changed?
