2011/6/21 Georg-Johann Lay <a...@gjlay.de>: > Denis Chertykov schrieb: >> 2011/6/20 Georg-Johann Lay <a...@gjlay.de>: >>> This is an optimization patch that implements extzv for 1-bit extracts. >> >> >>> +(define_insn_and_split "*extzv" >>> + [(set (match_operand:QI 0 "register_operand" >>> "=*d,*d,*d,r") >>> + (zero_extract:QI (match_operand:QI 1 "register_operand" >>> "0,r,0,r") >>> + (const_int 1) >>> + (match_operand:QI 2 "const_0_to_7_operand" >>> "L,L,P,n")))] >>> + "" >>> + "@ >>> + andi %0,1 >>> + mov %0,%1\;andi %0,1 >>> + lsr %0\;andi %0,1 >>> + bst %1,%2\;clr %0\;bld %0,0" >> >> Why you have a second constraint alternative (*d,r,L) ? >> IMHO it's unnecessary. > > The second alternative takes 2 instructions/ticks whereas the last > alternative -- which would be taken without alternative 2 -- takes 3 > instructions/ticks. As because of '*' there is no preference on > register class, allocator just sees "r,r,n" and if the output register > happens to end up in 'd' shorter sequences are possible in some cases. > But there is no pressure being put to get such an alternative; in > particular, allocator does not see "d,0,L" and does not emit a move to > reload input.
Ok. > >>> + && REGNO (operands[0]) >= 16" >> >> It's not a good practice to refer to register as number. >> >> Denis. > > Ok. d_register_operand or satisfies_constraint_d would do. But I > preferred to introduce a new constraint for 4 and avoid splitting > *extzv altogether to keep it simple. Complexity of splitting is not a > real advantage over writing things down directly. > > As avr is running out of constraint letters, I started 3-letter > constraints 'Y**' in the style of bfin. Would be nice if 'K' was not > already occupied or could be deprecated (is'n not really useful in > inline asm)... Better to choose starting letter different to pointer register names X,Y,Z. May be better to use underscore '_' ? Denis.
