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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ARM NEON vld3_u8 incorrect optimization"
href="https://bugs.llvm.org/show_bug.cgi?id=46105">46105</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>ARM NEON vld3_u8 incorrect optimization
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>10.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>guilder13@yandex-team.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
</td>
</tr></table>
<p>
<div>
<pre>Not sure if it's shortest snippet, but it's much less than original.
#include "arm_neon.h"
typedef unsigned char uint8;
typedef unsigned short uint16;
typedef short int16;
inline void decompressColor(const uint8 color_RGB444[3], uint8 color[3])
{
color[0] = (color_RGB444[0] << (8 - 4)) | (color_RGB444[0] >> (4 - (8-4)) );
color[1] = (color_RGB444[1] << (8 - 4)) | (color_RGB444[1] >> (4 - (8-4)) );
color[2] = (color_RGB444[2] << (8 - 4)) | (color_RGB444[2] >> (4 - (8-4)) );
}
#pragma clang optimize off
uint8x8_t noopt(uint8x8_t possible_colors_v[4][3], uint8x8x3_t rgba_u8[2])
{
// fake usage
}
#pragma clang optimize on
int calculateError59T_NEON(const uint8* srcimg, uint8 (colorsRGB444)[2][3],
uint8 &distance, unsigned int &pixel_indices,
int best_block_error = 65535)
{
// Problem line
uint8x8x3_t rgba_u8[2] = { vld3_u8(srcimg), vld3_u8(srcimg + 3 * 8) };
uint8 color0[3];
uint8 color1[3];
decompressColor(colorsRGB444[0], color0);
decompressColor(colorsRGB444[1], color1);
uint8x8_t possible_colors_v[4][3];
possible_colors_v[0][0] = vdup_n_u8(color0[0]);
possible_colors_v[0][1] = vdup_n_u8(color0[1]);
possible_colors_v[0][2] = vdup_n_u8(color0[2]);
possible_colors_v[2][0] = vdup_n_u8(color1[0]);
possible_colors_v[2][1] = vdup_n_u8(color1[1]);
possible_colors_v[2][2] = vdup_n_u8(color1[2]);
uint32x4_t best_block_error_v = vdupq_n_u32(best_block_error);
noopt(possible_colors_v, rgba_u8);
return best_block_error_v[0];
}
Not optimized code is too long to show it (around 37 lines), because of
intrinsics.
Optimization without surroundings is correct.
ld3 {v0.8b-v2.8b}, [x0], #24
stp d0, d1, [x1]
str d2, [x1,#16]
ld3 {v0.8b-v2.8b}, [x0]
stp d0, d1, [x1,#24]
str d2, [x1,#40]
Optimization with surrounding code.
ld3 {v1.8b-v3.8b}, [x0], #24
...
stp d0, d1, [x29,#-48]
ld3 {v0.8b-v2.8b}, [x0]
...
stp d3, d0, [x29,#-32]
stp d1, d2, [x29,#-16]
As you can see, it loads first part in v1-3, then stores d0, d1. Where d0 was
not even loaded, and so on.
We are using now these revisions.
CLANG_REVISION = '4e0d9925d6a3561449bdd8def27fd3f3f1b3fb9f'
CLANG_SVN_REVISION = 'n346557'
CLANG_SUB_REVISION = 2</pre>
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