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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Failure to remove redundant assume given alignment on call"
href="https://llvm.org/bugs/show_bug.cgi?id=25068">25068</a>
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<th>Summary</th>
<td>Failure to remove redundant assume given alignment on call
</td>
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<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<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>
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<th>Reporter</th>
<td>listmail@philipreames.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>This assume in the following test case should be removable.
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
declare align 8 i8* @get()
; Function Attrs: nounwind
declare void @llvm.assume(i1) #0
define void @test() {
%p = tail call align 8 i8* @get()
%ptrint = ptrtoint i8* %p to i64
%maskedptr = and i64 %ptrint, 7
%maskcond = icmp eq i64 %maskedptr, 0
tail call void @llvm.assume(i1 %maskcond)
ret void
}
I believe the problem is that ValueTracking hasn't been taught that the low
bits of an aligned pointer result are known to be zero.
Note that this example is particularly problematic since the inliner will
*introduce* @llvm.assume calls with this pattern. I haven't caught it
producing something quite this trivial, but I have seen cases where the IR
simplifies to something this simple.</pre>
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