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pan/mdg: Replicate swizzles for scalar sources

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This works around issue packing 32-bit scalar swizzles zero-extended to
64-bit, seen with the umul_high implementation. I tried for a while
figuring out the root cause (even rewrote a big chunk of disassembler)
but am still a bit lost. Nevertheless this is a safe workaround with no
performance impact (and avoids relying on NIR undefined behaviour to
implement GPU undefined behaviour), so let's do this for now to fix
umul_high.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17860>
This commit is contained in:
Alyssa Rosenzweig 2022-08-24 12:20:04 -04:00 • committed by Marge Bot
parent e951d6362c
commit 7b78e05ba8
1 changed files with 19 additions and 2 deletions
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21
src/panfrost/midgard/midgard_compile.c
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@ -661,10 +661,27 @@ mir_copy_src(midgard_instruction *ins, nir_alu_instr *instr, unsigned i, unsigne
ins->src[to] = nir_src_index(NULL, &src.src);
ins->src_types[to] = nir_op_infos[instr->op].input_types[i] | bits;
/* Figure out which component we should fill unused channels with. This
* doesn't matter too much in the non-broadcast case, but it makes
* should that scalar sources are packed with replicated swizzles,
* which works around issues seen with the combination of source
* expansion and destination shrinking.
*/
unsigned replicate_c = 0;
if (bcast_count) {
replicate_c = bcast_count - 1;
} else {
for (unsigned c = 0; c < NIR_MAX_VEC_COMPONENTS; ++c) {
if (nir_alu_instr_channel_used(instr, i, c))
replicate_c = c;
}
}
for (unsigned c = 0; c < NIR_MAX_VEC_COMPONENTS; ++c) {
ins->swizzle[to][c] = src.swizzle[
(!bcast_count || c < bcast_count) ? c :
(bcast_count - 1)];
((!bcast_count || c < bcast_count) &&
nir_alu_instr_channel_used(instr, i, c)) ?
c : replicate_c];
}
}