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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Dead Code Elimination Regression at -O3 (trunk vs 12.0.1)"
href="https://bugs.llvm.org/show_bug.cgi?id=52102">52102</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Dead Code Elimination Regression at -O3 (trunk vs 12.0.1)
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</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>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>theodoros.theodoridis@inf.ethz.ch
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>cat case.c
bisections
static int a, b = -2, c[1];
void foo(void);
int main() {
if ((c[0] &= (1 % b == 0)) > 1)
foo();
b = 1;
}
trunk can no longer eliminate foo:
clang-12 -v
clang version 12.0.1 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
fed41342a82f5a3a9201819a82bf7a48313e296b)
Target: x86_64-unknown-linux-gnu
clang-12 case.c -S -O3 -o /dev/stdout
...
main: # @main
.cfi_startproc
# %bb.0:
movzbl b(%rip), %eax
andl %eax, c.0(%rip)
movb $1, b(%rip)
xorl %eax, %eax
retq
clang-trunk -v
clang version 14.0.0 (<a href="https://github.com/llvm/llvm-project.git">https://github.com/llvm/llvm-project.git</a>
73346f58486d29c0d2687af1208fa146168d62d8)
Target: x86_64-unknown-linux-gnu
clang-trunk case.c -S -O3 -o /dev/stdout
...
main: # @main
.cfi_startproc
# %bb.0:
pushq %rax
.cfi_def_cfa_offset 16
movzbl b(%rip), %eax
andl c.0(%rip), %eax
movl %eax, c.0(%rip)
cmpl $2, %eax
jb .LBB0_2
# %bb.1:
callq foo
.LBB0_2:
movb $1, b(%rip)
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
retq
<a href="https://github.com/llvm/llvm-project/commit/183bbad1d78a4bf445ec4db1ce01673f6a7feb37">https://github.com/llvm/llvm-project/commit/183bbad1d78a4bf445ec4db1ce01673f6a7feb37</a>
introduced this regression</pre>
</div>
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