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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 flags from neg to eliminate test instruction"
href="https://bugs.llvm.org/show_bug.cgi?id=47661">47661</a>
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<tr>
<th>Summary</th>
<td>Reuse flags from neg to eliminate test instruction
</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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<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>
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<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
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<div>
<pre>foo(unsigned long long const*, unsigned long long*, unsigned long long):
# @foo(unsigned long long const*, unsigned long long*,
unsigned long long)
test rdx, rdx
je .LBB0_3
neg rdx
.LBB0_2: # =>This Inner Loop Header: Depth=1
mov rax, qword ptr [rdi + 8*rdx]
and qword ptr [rsi + 8*rdx], rax
inc rdx
jne .LBB0_2
.LBB0_3:
ret
Clang -Os:
foo(unsigned long long const*, unsigned long long*, unsigned long long):
# @foo(unsigned long long const*, unsigned long long*,
unsigned long long)
test rdx, rdx
je .LBB0_3
neg rdx
.LBB0_2: # =>This Inner Loop Header: Depth=1
mov rax, qword ptr [rdi + 8*rdx]
and qword ptr [rsi + 8*rdx], rax
inc rdx
jne .LBB0_2
.LBB0_3:
ret
GCC -O2:
foo(unsigned long long const*, unsigned long long*, unsigned long long):
neg rdx
je .L1
.L3:
mov rax, QWORD PTR [rdi+rdx*8]
and QWORD PTR [rsi+rdx*8], rax
add rdx, 1
jne .L3
.L1:
ret
<a href="https://godbolt.org/z/av85T1">https://godbolt.org/z/av85T1</a></pre>
</div>
</p>
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