[8u] RFR: fix java_calling_convention for longs

[Edward Nevill]

Hi Anton,

I see. Thanks for checking that. I will push your patch later.

All the best,
Ed.

On Mon, 2016-03-14 at 09:02 +0000, Anton Kozlov wrote:
> Hi Ed,
> 
> Thanks for review! Regarding T_DOUBLE: I beleive that 
> 
>     fp_args = round_to(fp_args, 2); // (3rd line of inlined code) 
> 
> will guard against descibed situation. If we came here with fp_args ==
> 15, then fp_args will be rounded first to 16 and then checked against
> FP_ArgReg_N boundary.
> 
> Java calling convention for floating point arguments looks like integer
> register arguments: adjacent single floats will occupy 2 single
> registers
> 
>     float, float, float -> f0, f1, f2
> 
> But if single float (placed to even single register) will be followed
> by double float, then one single register will not be used
> 
>     float, double, float -> f0, d1(f3:f2), f4 // f1 not used
> 
> Note, that C calling convention is different, it places third argument
> to f1 in last example.
> 
> Thanks,
> Anton
> 
> On Sun, 2016-03-13 at 15:07 +0000, Edward Nevill wrote:
> > Hi Anton,
> > 
> > Thanks for this. Your fix looks correct. Could you also check the
> > code for T_DOUBLE a few lines later.
> > 
> > 
> >     case T_DOUBLE:
> >       assert(sig_bt[i + 1] == T_VOID, "expecting half");
> >       fp_args = round_to(fp_args, 2);
> >       if (fp_args < FP_ArgReg_N) {
> >         regs[i].set2(FP_ArgReg[fp_args]->as_VMReg());
> >         fp_args += 2;
> >       } else {
> >         regs[i].set2(VMRegImpl::stack2reg(stk_args));
> >         stk_args += 2;
> >       }
> >       break;
> > 
> > Here it would seem then if fp_args was == 15 then it could end up
> > using f15 and f16 which is invalid? It can only do this if there is a
> > mixture of double and float arguments previously.
> > 
> > Thanks,
> > Ed.
> > 
> >