https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93453
--- Comment #5 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to HaoChen Gui from comment #4)
> (define_insn_and_split "*rotl<mode>3_insert_8"
> [(set (match_operand:GPR 0 "gpc_reg_operand" "=r")
> (plus_ior_xor:GPR (ashift:GPR (match_operand:GPR 1 "gpc_reg_operand"
> "r")
> (match_operand:SI 2 "const_int_operand"
> "n"))
> (match_operand:GPR 3 "gpc_reg_operand" "0")))]
> "INTVAL (operands[2]) > 0
> && (nonzero_bits (operands[3], <MODE>mode)
> < HOST_WIDE_INT_1U << INTVAL (operands[2]))"
> {
> if (<MODE>mode == SImode)
> return "rlwimi %0,%1,%h2,0,31-%h2";
> else
> return "rldimi %0,%1,%H2,0";
> }
> "&& 1"
> [(set (match_dup 0)
> (ior:GPR (and:GPR (match_dup 3)
> (match_dup 4))
> (ashift:GPR (match_dup 1)
> (match_dup 2))))]
> {
> operands[4] = GEN_INT ((HOST_WIDE_INT_1U << INTVAL (operands[2])) - 1);
> }
> [(set_attr "type" "insert")])
>
> But I found that nonzero_bits can't return an exact value except in combine
> pass.
It can return a different value after the combine pass, yes. But making the
version of nonzero_bits used by combine be the generic version would be a big
regression, and the version used by combine cannot be used anywhere else (it
was an extension of flow.c originally, but this wasn't ported to the dataflow
framework).
I planned to fix this for GCC 12, but we are in stage 3 already :-)
> So the pattern finally can't be split to pattern of
> 'rotl<mode>3_insert_3'. Also if the pass after combine changes the insn, it
> can't be recognized as the nonzero_bits doesn't return exact value in that
> pass.
>
> I am thinking if we can convert third operand to "reg and a mask" when the
> nonzero_bits is known in combine pass. Thus the pattern can be directly
> combined to 'rotl<mode>3_insert_3'.
>
> (set (reg:DI 123)
> (ior:DI (ashift:DI (reg:DI 125)
> (const_int 32 [0x20]))
> (reg:DI 126)))
>
> (set (reg:DI 123)
> (ior:DI (ashift:DI (reg:DI 125)
> (const_int 32 [0x20]))
> (and:DI (reg:DI 126)
> (const_int 4294967295 [0xfffffff]))))
Will nothing modify it back?
