> > > > _Bool iftmp.0_113;
> > > > _Bool iftmp.0_114;
> > > > iftmp.0_113 = .MASK_LOAD (_170, 8B, _169, _171(D));
> > > > iftmp.0_114 = _47 | iftmp.0_113;
> > _BoolD.2746 _47;
> > iftmp.0_114 = _47 ? 1 : iftmp.0_113;
> > which is folded into
> > iftmp.0_114 = _47 | iftmp.0_113;
>
> _47 was the .MASK_LOAD def, right?
_47 is the inverted load mask, iftmp.0_113 is the MASK_LOAD result.
Its mask is _169 where _169 = ~_47;
> It's not exactly obvious what goes wrong - the transform above
> is correct - it's only "unexpected" for the lanes that were
> masked. So the actual bug must be downstream from iftmp.0_144.
>
> I think one can try to reason on the ifcvt (scalar) code by
> assuming the .MASK_LOAD def would be undefined. Then we'd
> have _47(D) ? 1 : iftmp.0_133 -> _47(D) | iftmp.0_133, I think
> that's at most phishy as the COND_EXPR has a well-defined
> value while the IOR might spill "undefined" elsewhere causing
> divergence. Is that what is actually happening?
After vectorization we recognize the mask (_47) as degenerate,
i.e. all ones and, conversely, the masked load mask (_169) is all zeros.
So we shouldn't really load anything.
Optimized we have
vect_patt_384.36_436 = .MASK_LEN_GATHER_LOAD (_435, vect__47.35_432, 1, { 0,
... }, { 0, ... }, _471, 0);
vect_iftmp.37_439 = vect_patt_384.36_436 | { 1, ... };
We then re-use a non-zero vector register as masked load result. Its
stale values cause the wrong result (which should be 1 everywhere).
--
Regards
Robin
