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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 - Suboptimal code generation for binary-operator parameter pack expansion."
href="https://bugs.llvm.org/show_bug.cgi?id=43023">43023</a>
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<th>Summary</th>
<td>Suboptimal code generation for binary-operator parameter pack expansion.
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
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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>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
<tr>
<th>Reporter</th>
<td>mike.k@digitalcarbide.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Given the following C++2a code:
bool ref (int a) {
return (a == -1) | (a == 0) | (a == 3) | (a == 4) | (a == 5);
}
bool test (int a) {
return [a](auto... args) {
return ((a == args) | ...);
}(-1, 0, 3, 4, 5);
}
The following LLVM IR is produced with -O3:
define dso_local zeroext i1 @_Z3refi(i32 %0) local_unnamed_addr #0 {
%2 = add i32 %0, 1
%3 = icmp ult i32 %2, 2
%4 = add i32 %0, -3
%5 = icmp ult i32 %4, 3
%6 = or i1 %5, %3
ret i1 %6
}
define dso_local zeroext i1 @_Z4testi(i32 %0) local_unnamed_addr #1 {
%2 = icmp eq i32 %0, 3
%3 = or i32 %0, 1
%4 = icmp eq i32 %3, 5
%5 = or i1 %2, %4
%6 = add i32 %0, 1
%7 = icmp ult i32 %6, 2
%8 = or i1 %7, %5
ret i1 %8
}
Resulting in the following x86-64 assembly:
ref(int): # @ref(int)
lea eax, [rdi + 1]
cmp eax, 2
setb cl
add edi, -3
cmp edi, 3
setb al
or al, cl
ret
test(int): # @test(int)
cmp edi, 3
sete al
mov ecx, edi
or ecx, 1
cmp ecx, 5
sete cl
or cl, al
add edi, 1
cmp edi, 2
setb al
or al, cl
ret
It appears as though a different pattern is being generated when expanding the
parameter pack along with the binary-or operator, and is not being optimized in
the same fashion.</pre>
</div>
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