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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=52592">52592</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 bar(void);
void foo(void);
static char b = 1;
static int c;
static int d(int e) { return e; }
int main() {
b = 0;
bar();
c = d(2048);
if (!((((0 == c || b) && 1) ^ 2)% 5))
{
d(0);
foo();
}
}
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:
pushq %rax
.cfi_def_cfa_offset 16
callq bar
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
retq
.Lfunc_end0:
clang-trunk -O3 -S -o /dev/stdout case.c
main: # @main
.cfi_startproc
# %bb.0:
pushq %rax
.cfi_def_cfa_offset 16
movb $1, b(%rip)
callq bar
movzbl b(%rip), %eax
xorl $1, %eax
orl $2, %eax
imull $-858993459, %eax, %eax # imm = 0xCCCCCCCD
cmpl $858993459, %eax # imm = 0x33333333
jbe .LBB0_1
# %bb.2:
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
retq
.LBB0_1:
.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>
38ed1db7e8740fce236d1893ff9e20cc22ef0ada)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Started with
<a href="https://github.com/llvm/llvm-project/commit/e7249e4acf3cf9438d6d9e02edecebd5b622a4dc">https://github.com/llvm/llvm-project/commit/e7249e4acf3cf9438d6d9e02edecebd5b622a4dc</a></pre>
</div>
</p>
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