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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 13.0.0)"
href="https://bugs.llvm.org/show_bug.cgi?id=52261">52261</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Dead Code Elimination Regression at -O3 (trunk vs 13.0.0)
</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>theodort@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 test.c
void foo(void);
void bar(void);
static char b = 2;
static int d = -2, e;
static int a(int f, int g) { return (g & -g) < 0 ? f : f - g; }
int main() {
d = 0;
d = b;
bar();
e = a(0, 0);
if (a(-2, d) > 1)
foo();
}
13.0.0 at -O3 can eliminate the call to foo but trunk cannot:
clang-13 -O3 -S -o /dev/stdout test.c
...
main: # @main
.cfi_startproc
# %bb.0:
pushq %rax
.cfi_def_cfa_offset 16
movb $1, d(%rip)
callq bar
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
retq
clang-trunk -O3 -S -o /dev/stdout case13_clean.c
...
main: # @main
.cfi_startproc
# %bb.0:
pushq %rax
.cfi_def_cfa_offset 16
movb $1, d(%rip)
callq bar
movzbl d(%rip), %eax
leal -2(,%rax,4), %ecx
movl %eax, %edx
shll $2, %edx
movl $2, %esi
subl %edx, %esi
testl %esi, %ecx
js .LBB0_3
# %bb.1:
leal -1(,%rax,4), %eax
cmpl $-3, %eax
jg .LBB0_3
# %bb.2:
callq foo
.LBB0_3:
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
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>
eda2ebd7807376829eb880c39623f364b438971f)
Target: x86_64-unknown-linux-gnu
Thread model: posix
<a href="https://github.com/llvm/llvm-project/commit/da210f5d3425e8877ceabaf6ed3483d52cbd7448">https://github.com/llvm/llvm-project/commit/da210f5d3425e8877ceabaf6ed3483d52cbd7448</a>
introduced this regression</pre>
</div>
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