Hi
Several comments before the new version of the patch.
1) x != x
I am happy to adjust constant_boolean_node, but look at the code
around line 9074 in fold-const.c, you will see that x <op> x
elimination, even with adjusted constant_boolean_node, will look about
the same as my code. Because I need to check the parameters (!FLOAT_P,
HONOR_NANS) on TREE_TYPE (arg0) not arg0, and I need to construct
constant_boolean_node (-1), not 1 in case of true.
But I will change constant_boolean_node to accept vector types.
2) comparison vs vcond
v = v1 < v2;
v = v1 < v2 ? {-1,...} : {0,...};
are not the same.
16,25c16,22
< movdqa .LC1(%rip), %xmm1
< pshufd $225, %xmm1, %xmm1
< pshufd $39, %xmm0, %xmm0
< movss %xmm2, %xmm1
< pshufd $225, %xmm1, %xmm1
< pcmpgtd %xmm1, %xmm0
< pcmpeqd %xmm1, %xmm1
< pcmpeqd %xmm1, %xmm0
< pand %xmm1, %xmm0
< movdqa %xmm0, -24(%rsp)
---
> pshufd $39, %xmm0, %xmm1
> movdqa .LC1(%rip), %xmm0
> pshufd $225, %xmm0, %xmm0
> movss %xmm2, %xmm0
> pshufd $225, %xmm0, %xmm0
> pcmpgtd %xmm0, %xmm1
> movdqa %xmm1, -24(%rsp)
So I would keep the hook, it could be removed at any time when the
standard expansion will start to work fine.
3) mask ? vec0 : vec1
So no, I don't think we need to convert {3, 4, -1, 5} to {0,0,-1,0}
(that would surprise my anyway, I'd have expected {-1,-1,-1,-1} ;)).
Does OpenCL somehow support you here?
OpenCL says that vector operation mask ? vec0 : vec1 is the same as
select (vec0, vec1, mask). The semantics of select operation is the
following:
gentype select (gentype a, gentype b, igentype c)
For each component of a vector type,
result[i] = if MSB of c[i] is set ? b[i] : a[i].
I am not sure what they really understand using the term MSB. As far
as I know MSB is Most Significant Bit, so does it mean that in case of
3-bit integer 100 would trigger true but 011 would be still false...
My reading would be that if all bits set, then take the first element,
otherwise the second.
It is also confusing when a ? vec0 : vec1, and a != 0 ? vec0 vec1
produce different results. So I would stick to all bits set being true
scenario.
4) Backend stuff. Ok, we could always fall back to reject the cases
when cond and operands have different type, and then fix the backend.
Adjustments are coming.
Artem.
