On Thu, Sep 5, 2024 at 3:10 PM Jeff Law <jeffreya...@gmail.com> wrote: > On 9/5/24 6:16 AM, Raphael Zinsly wrote: > > On Wed, Sep 4, 2024 at 8:32 PM Jeff Law <j...@ventanamicro.com> wrote: > >> On 9/2/24 2:01 PM, Raphael Moreira Zinsly wrote: > >> ... > >>> + bool bit31 = (hival & 0x80000000) != 0; > >>> + int trailing_shift = ctz_hwi (loval) - ctz_hwi (hival); > >>> + int leading_shift = clz_hwi (loval) - clz_hwi (hival); > >>> + int shiftval = 0; > >>> + > >>> + /* Adjust the shift into the high half accordingly. */ > >>> + if ((trailing_shift > 0 && hival == (loval >> trailing_shift)) > >>> + || (trailing_shift < 0 && hival == (loval << trailing_shift))) > >>> + shiftval = 32 - trailing_shift; > >>> + else if ((leading_shift < 0 && hival == (loval >> leading_shift)) > >>> + || (leading_shift > 0 && hival == (loval << leading_shift))) > >> Don't these trigger undefined behavior when tailing_shift or > >> leading_shift is < 0? We shouldn't ever generate negative shift counts. > > > > The value of trailing/leading_shift is added to 32, we will never have > > negative shift counts. > In the IF you have this conditional: > > > (trailing_shift < 0 && hival == (loval << trailing_shift)) > > How could that not be undefined behvaior? You first test that the value > is less than zero and if it is less than zero you use it as a shift count.
I'm not using trailing_shift as the shift count, I'm using shiftval: + /* Now we want to shift the previously generated constant into the + high half. */ + alt_codes[alt_cost - 2].code = ASHIFT; + alt_codes[alt_cost - 2].value = shiftval; + alt_codes[alt_cost - 2].use_uw = false; + alt_codes[alt_cost - 2].save_temporary = false; -- Raphael Moreira Zinsly
