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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Reuse ZF flags from xor; remove cmp"
href="https://bugs.llvm.org/show_bug.cgi?id=43014">43014</a>
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</tr>
<tr>
<th>Summary</th>
<td>Reuse ZF flags from xor; remove cmp
</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>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
</td>
</tr></table>
<p>
<div>
<pre>#include <stdlib.h>
#include <stdio.h>
int p;
__attribute_noinline__ int foo(int x, int y) {
p = x ^ y;
if (x - y == 0) abort();
return 0;
}
int main(int argc, char**argv) {
foo(argc, atoi(argv[1]));
printf("p = %d\n", p);
}
foo: # @foo
.cfi_startproc
# %bb.0: # %entry
pushq %rax
.cfi_def_cfa_offset 16
movl %esi, %eax
xorl %edi, %eax
movl %eax, p(%rip)
cmpl %esi, %edi
je .LBB0_2
XOR sets ZF flag so.. I tried to remove cmp and compiled hand modified asm..
foo: # @foo
.cfi_startproc
# %bb.0: # %entry
pushq %rax
.cfi_def_cfa_offset 16
movl %esi, %eax
xorl %edi, %eax
movl %eax, p(%rip)
jz .LBB0_2
and test case still works as expected.</pre>
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