On Tue, Jun 24, 2014 at 02:32:46PM -0700, Richard Henderson wrote:
> On 06/24/2014 02:24 PM, Al Viro wrote:
> > Al, off to figure out the black magic TCG is using to generate calls...
>
> If you've a helper
>
> DEF_HELPER_1(halt, void, i64)
>
> then
>
> gen_helper_halt(...)
>
> will generate the tcg ops that result in the call.
Another fun issue:
CVTTQ is both underreporting the overflow *AND* reports the wrong kind - FOV
instead of IOV.
* it misses reporting overflows for case when it *knows* that
overflow will happen - the need to shift up by more than 63 bits.
Trivially fixed, of course. There overflow cases leave wrong
result as well - should be 0.
* it also misses reporting overflows for case when value is in
ranges 2^63..2^64-1 and -2^64+1..-2^63-1. And yes, it's
asymmetric - 2^63 is an overflow, -2^63 isn't.
* overflow is reported by float_raise(float_flag_overflow, &FP_STATUS).
Wrong flag - it should be IOV, not FOV. And it should be set
in FPCR regardless of the trap modifier (IOV, this VI thing is
wrong - we should deal with that only when we generate a trap).
* All overflow cases should raise INE as well.
Could we steal bit 1 in float_exception_flags for IOV? It is (currently?)
unused -
enum {
float_flag_invalid = 1,
float_flag_divbyzero = 4,
float_flag_overflow = 8,
float_flag_underflow = 16,
float_flag_inexact = 32,
float_flag_input_denormal = 64,
float_flag_output_denormal = 128
};
That would allow to deal with that crap nicely - we could have it raise
the new flag, then have helper_fp_exc_raise_... for default trap mode
mask it out (and yes, we need to set FPCR flags in default mode, as well
as /U and /V - confirmed by direct experiment *and* by TFM).
If we can't... well, we could put that flag separately, but it would be
more unpleasant. Folks?
