Wrong optimization from ‘fwprop’ pass

[Jojo R]

insn seqs:

s1:

        __builtin_set_float_convert_mode(0);
        r1 = __builtin_load(a1, a2);
        r2 = __builtin_float_convert(r1);
        __builtin_store(a3, r2);
        __builtin_set_float_convert_mode(0);

s2:
        __builtin_set_float_convert_mode(1);
        r1 = __builtin_load(a1, a2);
        r2 = __builtin_float_convert(r1);
        __builtin_store(a3, r2);
        __builtin_set_float_convert_mode(0);


the diference of s1 and s2 only is "__builtin_set_float_convert_mode"

from beginning, the s1 mode is set 0, but s2 mode is set 1.

From optimization 'fwprop', the s2 insn seqs is deleted

as dead code with compiler option ‘-O3', is it gcc bug ?


builtin patten of __builtin_set_float_convert_mode:

(define_insn "target_fcvtmode"
 [(set (reg:SI FCVTMODE_REGNUM)
 (unspec_volatile:SI [(match_operand:SI 0 "operand" "rK")] UNSPECV_FCVTMODE))]
 ""
 "fcvtmode\t%1"
)


builtin patten of __builtin_set_float_convert_mode:

(define_insn "target_fcvt"
 [(set (match_operand:SI 0 "register_operand" "=r")
 (unspec:SI [(match_operand:SF 1 "register_operand" "f")]
 UNSPEC_FCVT))
 (use (reg:SI FCVTMODE_REGNUM))]
 ""
 "fcvt\t%0,%1"
)


As far as i know, __builtin_set_float_convert_mode depend on 'FCVTMODE_REGNUM' 
which is from
__builtin_set_float_convert_mode, it's not dead code.

or something wrong in my pattens ?

Anyone could give me some hints ?

Thanks

Jojo