BImode is treated as normal byte-wide mode and causes bug.

[Paolo Bonzini]

On 12/20/2010 12:43 PM, Claudiu Zissulescu wrote:
> Hi,
>
> Why don't you use a define_insn "zero_extendbisi2" which generates
> your conversion instruction.

You're right that this should be a valid workaround, but Bingfeng 
reported a bug indeed.

(zero_extend:SI (reg:BI 120))

should have been transformed to

(and:SI (subreg:SI (reg:BI 120) 0)
     (const_int 1 [0xff]))

and

(subreg:QI (zero_extend:SI (reg:BI 120)) 0)

to

(and:QI (subreg:QI (reg:BI 120) 0)
     (const_int 1 [0xff]))

That said, his observation that

> Grep GET_MODE_PRECISION returns not many results.

... misses that GET_MODE_MASK will also return the correct value for 
fractional integer modes.  This macro has quite a few occurrences in 
combine and elsewhere.

Paolo