gallivm: (trivial) fix lp_build_concat_n

The code was designed to handle no-op concat but failed (unless the
caller was using same pointer for src and dst).

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
gallivm: enhance special sse2 4x4f and 2x8f -> 1x16ub conversion

There's no good reason why it can't handle 2x4f->1x8ub, 1x4f->1x4ub and
1x8f->1x8ub cases, there might be legitimate reasons why we don't have
enough input vectors for a full destination vector, and using pack
intrinsics should still be much better than using generic conversion
(it looks like convert_alpha from the blend code might hit this though
I suspect it could be avoided).

v2: add another test vector format to lp_test_conv so this gets tested.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
llvmpipe: cleanup of generate_unswizzled_blend

Some parameters were used inconsistently, for instance not using
block_width/block_height/block_size for deferring number of pixels
but rather relying on guesses from the number of fragment shaders etc,
so fix this up (no actual change in behavior since the block size stays
fixed). (Though most of the code would work with different block_height,
with three exceptions, one being the hacked r11g11b10 conversions and
twiddle code which only work with block_height 2 not 1, and the last
one being blend vector type not being 128bit wide.)

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
llvmpipe: reduce alignment requirement for 1d resources from 4x4 to 4x1

For rendering to buffers, we cannot have any y alignment.
So make sure that tile clear commands only clear up to the fb width/height,
not more (do this for all resources actually as clearing more seems
pointless for other resources too). For the jit fs function, skip execution
of the lower half of the fragment shader for the 4x4 stamp completely,
for depth/stencil only load/store the values from the first row
(replace other row with undef).
For the blend function, also only load half the values from fs output,
replace the rest with undefs so that everything still operates on the
full 4x4 block to keep code the same between 4x1 and 4x4 (except for
load/store of course which also needs to skip (store) or replace these
values with undefs (load))., at the cost of slightly less optimal code
being produced in some cases.
Also reduce 1d and 1d array alignment too, because they can be handled the
same as buffers so don't need to waste memory.

v2: don't try to run special blend code for 4x1, (very) slightly less
complexity if we just use the same code as for 4x4 which may or may not
make it easier to optimize in the future (as we care a lot more about 4x4
performance than 1d).

v2: don't use undef values for unused fs src outputs with llvm 3.1 as it
apparently can trigger a bug in llvm.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
llvmpipe: improve alignment calculation for fetching/storing pixels

This was always doing per-pixel alignment which isn't necessary, except
for the buffer case (due to the per-element offset). The disabled code
for calculating it was incorrect because it assumed that always the full
block would be fetched, which may not be the case, so fix this up.
The original code failed for instance for r10g10b10a2 the alignment would
have been calculated as 4 (block_width) * 4 (bytes) so 16, but the actual
fetch may have only fetched 2 values at a time, hence only alignment 8 -
it is unclear what exactly would happen in this case (alignment larger
than size to fetch).
So just use the (already calculated) fetch size instead and get alignment
from that which should always work, no matter if fetching 1,2 or 4 pixels.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>