sign_extending to values wider than hard registers

[Jim Wilson]

d9910490@est.fib.upc.es wrote:
> (define_insn "extendhisi2"
>     [(set (subreg:SI (match_operand:HI 0 "register_operand" "=r") 4)
>           (sign_extend:SI (match_operand:HI 1 "register_operand" "r")))]

Don't use subregs like that.  Just (match_opreand:SI 0 ...).

> I am worried about that, because when expanding a value placed in R0 (for
> instance), then gcc assumes that R1 has the sign_extension (which is false,
> because nobody has put it there).

It is your responsibility to emit assembler code for the extendhisi2 
pattern that puts the sign_extension bits in R1.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com