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nir: for nir_shift_channels, fill undefined components with undef instead of .x

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This potentially results in better code because we don't add def uses where
undef is allowed.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38468>
This commit is contained in:
Marek Olšák 2025-11-05 16:12:47 -05:00 • committed by Marge Bot
parent 65837d8289
commit 22871fb8bd
1 changed files with 11 additions and 8 deletions
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19
src/compiler/nir/nir_builder.h
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@ -1645,9 +1645,9 @@ nir_resize_vector(nir_builder *b, nir_def *src, unsigned num_components)
return nir_trim_vector(b, src, num_components);
}
/* Shift channels to the left or right. Fill undefined components with .x.
/* Shift channels to the left or right. Fill undefined components with undef.
* Examples:
* channel_shift = 1, new_num_components = 4: .xyzw -> .xxyz
* channel_shift = 1, new_num_components = 4: .xyzw -> ._xyz
* channel_shift = -1, new_num_components = 3: .xyzw -> .yzw
*/
static inline nir_def *
@ -1657,15 +1657,18 @@ nir_shift_channels(nir_builder *b, nir_def *def, int channel_shift,
if (channel_shift == 0)
return nir_resize_vector(b, def, new_num_components);
assert(abs(channel_shift) < NIR_MAX_VEC_COMPONENTS);
unsigned swizzle[NIR_MAX_VEC_COMPONENTS] = {0};
nir_def *chan[NIR_MAX_VEC_COMPONENTS];
for (int i = 1; i < def->num_components; i++) {
if (i + channel_shift >= 0)
swizzle[i + channel_shift] = i;
for (int i = 0; i < (int)new_num_components; i++) {
int src_index = i - channel_shift;
if (src_index >= 0 && src_index < def->num_components)
chan[i] = nir_channel(b, def, src_index);
else
chan[i] = nir_undef(b, 1, def->bit_size);
}
return nir_swizzle(b, def, swizzle, new_num_components);
return nir_vec(b, chan, new_num_components);
}
nir_def *