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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 - gvn produces wrong code with "opt -inline -mem2reg -instcombine -licm -reg2mem -memcpyopt -gvn""
href="https://bugs.llvm.org/show_bug.cgi?id=41721">41721</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>gvn produces wrong code with "opt -inline -mem2reg -instcombine -licm -reg2mem -memcpyopt -gvn"
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>cszide@163.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=21883" name="attach_21883" title=".bc file of the source code">attachment 21883</a> <a href="attachment.cgi?id=21883&action=edit" title=".bc file of the source code">[details]</a></span>
.bc file of the source code
$clang -v
clang version 9.0.0 (trunk 355281)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/jack-zhou/Documents/llvm/llvm_truck/llvm/build4/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.3.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$clang -O3 -c -emit-llvm -mllvm -disable-llvm-optzns small.c
$clang small.bc -o small1.out && ./small1.out
84957F6D
$opt -inline -mem2reg -instcombine -licm -reg2mem -memcpyopt -gvn small.bc -o
small-opt.bc
$clang small-opt.bc -o small2.out && ./small2.out
0
without gvn, the result is correct.
$opt -inline -mem2reg -instcombine -licm -reg2mem -memcpyopt small.bc -o
small-opt1.bc
$clang small-opt1.bc -o small3.out && ./small3.out
84957F6D
---------------------------------------------
#include<stdio.h>
typedef unsigned char uint8_t;
typedef unsigned int uint32_t;
typedef unsigned long int uint64_t;
static uint32_t crc32_tab[256];
static uint32_t crc32_context = 0xFFFFFFFFUL;
static void crc32_gentab (void)
{
uint32_t crc;
const uint32_t poly = 0xEDB88320UL;
int i, j;
for (i = 0; i < 256; i++) {
crc = i;
for (j = 8; j > 0; j--) {
if (crc & 1) {
crc = (crc >> 1) ^ poly;
} else {
crc >>= 1;
}
}
crc32_tab[i] = crc;
}
}
static void crc32_byte (uint8_t b) {
crc32_context =
((crc32_context >> 8) & 0x00FFFFFF) ^
crc32_tab[(crc32_context ^ b) & 0xFF];
}
static void crc32_8bytes (uint64_t val)
{
crc32_byte ((val>>0) & 0xff);
crc32_byte ((val>>8) & 0xff);
crc32_byte ((val>>16) & 0xff);
crc32_byte ((val>>24) & 0xff);
crc32_byte ((val>>32) & 0xff);
crc32_byte ((val>>40) & 0xff);
crc32_byte ((val>>48) & 0xff);
crc32_byte ((val>>56) & 0xff);
}
static void transparent_crc (uint64_t val)
{
crc32_8bytes(val);
}
int a=0, b=0, c=0;
void main() {
crc32_gentab();
for (; b < 9; b++) {
c = 0;
for (; c < 3; c++)
transparent_crc(a);
}
printf("%lX\n",crc32_context ^ 0xFFFFFFFFUL);
}</pre>
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