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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 - [EarlyCSE] recognize commutative intrinsics with >2 args"
href="https://bugs.llvm.org/show_bug.cgi?id=47410">47410</a>
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<th>Summary</th>
<td>[EarlyCSE] recognize commutative intrinsics with >2 args
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
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<pre>EarlyCSE was enhanced to recognize intrinsics that are commutative
(<a href="https://reviews.llvm.org/D86798">https://reviews.llvm.org/D86798</a>), but it is currently restricted to arguments
with exactly 2 args.
But there are a small set of intrinsics that have commutative first 2 operands
with extra args after that:
declare i16 @llvm.smul.fix.i16(i16, i16, i32)
define i16 @intrinsic_3_args(i16 %x, i16 %y) {
%m1 = call i16 @llvm.smul.fix.i16(i16 %x, i16 %y, i32 1)
%m2 = call i16 @llvm.smul.fix.i16(i16 %y, i16 %x, i32 1)
%r = sub i16 %m1, %m2
ret i16 %r
}
$ opt commute.ll -S -gvn
define i16 @intrinsic_3_args(i16 %x, i16 %y) {
%m1 = call i16 @llvm.smul.fix.i16(i16 %x, i16 %y, i32 1)
ret i16 0
}
$ opt commute.ll -S -early-cse
define i16 @intrinsic_3_args(i16 %x, i16 %y) {
%m1 = call i16 @llvm.smul.fix.i16(i16 %x, i16 %y, i32 1)
%m2 = call i16 @llvm.smul.fix.i16(i16 %y, i16 %x, i32 1)
%r = sub i16 %m1, %m2
ret i16 %r
}</pre>
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