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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 - Are we missing nsw/nuw tags on vector operations?"
href="https://bugs.llvm.org/show_bug.cgi?id=43399">43399</a>
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<th>Summary</th>
<td>Are we missing nsw/nuw tags on vector operations?
</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>Windows NT
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, nunoplopes@sapo.pt, spatel+llvm@rotateright.com
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<pre>Split off from <a class="bz_bug_link
bz_status_NEW "
title="NEW - Failed to combine -smax(-x,-y) to smin(x,y)"
href="show_bug.cgi?id=43310">https://bugs.llvm.org/show_bug.cgi?id=43310</a>
<a href="https://gcc.godbolt.org/z/iOcKcj">https://gcc.godbolt.org/z/iOcKcj</a>
#include <stdint.h>
#include <x86intrin.h>
auto add_i32(int x, int y) {
return x + y;
}
auto add_v4i32(__v4si x, __v4si y) {
return x + y;
}
clang -g0 -O3 -march=btver2 -emit-llvm
define i32 @add_i32(i32 %0, i32 %1) {
%3 = add nsw i32 %1, %0
ret i32 %3
}
define <4 x i32> @add_v4i32(<4 x i32> %0, <4 x i32> %1) {
%3 = add <4 x i32> %1, %0
ret <4 x i32> %3
}
While we tag the scalar op with nsw we fail to do this for the vector version.
If we explicitly reduce the range of the vector values then nsw does reappear:
auto add_ashr_v4i32(__v4si x, __v4si y) {
x >>= 15;
y >>= 15;
return x + y;
}
define <4 x i32> @add_ashr_v4i32(<4 x i32> %0, <4 x i32> %1) {
%3 = ashr <4 x i32> %0, <i32 15, i32 15, i32 15, i32 15>
%4 = ashr <4 x i32> %1, <i32 15, i32 15, i32 15, i32 15>
%5 = add nsw <4 x i32> %4, %3
ret <4 x i32> %5
}</pre>
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