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softfloat: Handle default NaN mode after pickNaNMulAdd, not before

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It is implementation defined whether a multiply-add of
(0,inf,qnan) or (inf,0,qnan) raises InvalidaOperation or
not, so we let the target-specific pickNaNMulAdd function
handle this. This means that we must do the "return the
default NaN in default NaN mode" check after the call,
not before. Correct the ordering, and restore the comment
from the old propagateFloat64MulAddNaN() that warned about
this corner case.

This fixes a regression from 2.11 for Arm guests where we would
incorrectly fail to set the Invalid flag for these cases.

Backports commit 1839189bbf89889076aadf0c793c1b57977b28d7 from qemu
This commit is contained in:
Peter Maydell 2018-05-14 07:24:25 -04:00 committed by Lioncash
parent bb95f85569
commit 150125de3f
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GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 30 additions and 22 deletions
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52
qemu/fpu/softfloat.c
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@ -602,34 +602,42 @@ static FloatParts pick_nan(FloatParts a, FloatParts b, float_status *s)
static FloatParts pick_nan_muladd(FloatParts a, FloatParts b, FloatParts c,
bool inf_zero, float_status *s)
{
int which;
if (is_snan(a.cls) || is_snan(b.cls) || is_snan(c.cls)) {
s->float_exception_flags |= float_flag_invalid;
}
if (s->default_nan_mode) {
a.cls = float_class_dnan;
} else {
switch (pickNaNMulAdd(is_qnan(a.cls), is_snan(a.cls),
is_qnan(b.cls), is_snan(b.cls),
is_qnan(c.cls), is_snan(c.cls),
inf_zero, s)) {
case 0:
break;
case 1:
a = b;
break;
case 2:
a = c;
break;
case 3:
a.cls = float_class_dnan;
return a;
default:
g_assert_not_reached();
}
which = pickNaNMulAdd(is_qnan(a.cls), is_snan(a.cls),
is_qnan(b.cls), is_snan(b.cls),
is_qnan(c.cls), is_snan(c.cls),
inf_zero, s);
a.cls = float_class_msnan;
if (s->default_nan_mode) {
/* Note that this check is after pickNaNMulAdd so that function
* has an opportunity to set the Invalid flag.
*/
a.cls = float_class_dnan;
return a;
}
switch (which) {
case 0:
break;
case 1:
a = b;
break;
case 2:
a = c;
break;
case 3:
a.cls = float_class_dnan;
return a;
default:
g_assert_not_reached();
}
a.cls = float_class_msnan;
return a;
}