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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missing transformation rotate(x) == 0 to x == 0"
href="https://bugs.llvm.org/show_bug.cgi?id=51566">51566</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missing transformation rotate(x) == 0 to x == 0
</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>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</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>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>bool test1(unsigned long long x)
{
unsigned long long r = (x << 32) | (x >> 32);
return r != 0;
}
bool test2(unsigned long long x)
{
unsigned long long r = (x << 32) | (x >> 32);
return r == ~0ULL;
}
Trunk -O3:
test1(unsigned long long): # @test1(unsigned long
long)
rol rdi, 32
test rdi, rdi
setne al
ret
test2(unsigned long long): # @test2(unsigned long
long)
rol rdi, 32
cmp rdi, -1
sete al
ret
test3(unsigned long long): # @test3(unsigned long
long)
rol rdi, 32
test rdi, rdi
setne al
ret
Current codegen:
<a href="https://godbolt.org/z/q78xxhWe4">https://godbolt.org/z/q78xxhWe4</a>
----------------------------------------
define i1 @src(i64 %0) {
%1:
%2 = fshr i64 %0, i64 %0, i64 32
%3 = icmp ne i64 %2, 0
ret i1 %3
}
=>
define i1 @tgt(i64 %0) {
%1:
%2 = icmp ne i64 %0, 0
ret i1 %2
}
Transformation seems to be correct!
----------------------------------------
define i1 @src(i64 %0) {
%1:
%2 = fshr i64 %0, i64 %0, i64 32
%3 = icmp ne i64 %2, -1
ret i1 %3
}
=>
define i1 @tgt(i64 %0) {
%1:
%2 = icmp ne i64 %0, -1
ret i1 %2
}
Transformation seems to be correct!
Alive:
<a href="https://alive2.llvm.org/ce/z/kmrBvv">https://alive2.llvm.org/ce/z/kmrBvv</a></pre>
</div>
</p>
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