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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 - Dead Code Elimination Regression at -O3 (trunk vs 13.0.0)"
href="https://bugs.llvm.org/show_bug.cgi?id=52580">52580</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 case.c
void foo(void);
static int b;
static int *e = &b;
static char a(char f) { return f < 0 ? f : 0; }
static char c(unsigned char f, int g) { return f >> g; }
int main() {
int h = *e;
*e = a(h);
if (c(h, 1)){
if (h)
*e = 0;
else
foo();
}
c(0, 0);
}
trunk cannot eliminate the call to foo but 13.0.0 can:
clang-13.0.0 -O3 -S -o /dev/stdout case.c
main: # @main
.cfi_startproc
# %bb.0:
xorl %eax, %eax
retq
.Lfunc_end0:
.size main, .Lfunc_end0-main
.cfi_endproc
# -- End function
clang-trunk -O3 -S -o /dev/stdout case.c
main: # @main
.cfi_startproc
# %bb.0:
pushq %rax
.cfi_def_cfa_offset 16
movl b(%rip), %eax
xorl %ecx, %ecx
testb %al, %al
movsbl %al, %edx
cmovsl %edx, %ecx
movl %ecx, b(%rip)
cmpb $2, %dl
jb .LBB0_4
# %bb.1:
testl %eax, %eax
je .LBB0_3
# %bb.2:
movl $0, b(%rip)
.LBB0_4:
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
retq
.LBB0_3:
.cfi_def_cfa_offset 16
callq foo
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
retq
.Lfunc_end0:
clang-trunk -v
clang version 14.0.0 (<a href="https://github.com/llvm/llvm-project">https://github.com/llvm/llvm-project</a>
dc9b5550b2238d65bcaa937c412d51802d819aeb)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Started with
<a href="https://github.com/llvm/llvm-project/commit/cfb6dfcbd13b417f83d8adca69b60ba4254b4233">https://github.com/llvm/llvm-project/commit/cfb6dfcbd13b417f83d8adca69b60ba4254b4233</a></pre>
</div>
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