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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [missed optimization] LLVM leaves behind no-op lifetime.end cleanup"
href="https://bugs.llvm.org/show_bug.cgi?id=45296">45296</a>
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<th>Summary</th>
<td>[missed optimization] LLVM leaves behind no-op lifetime.end cleanup
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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>Transformation Utilities
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>rnk@google.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<pre>Seems related to issue 44329
Consider:
$ cat t.cpp
struct NoopDtor { ~NoopDtor() {} };
void mayThrow(NoopDtor *);
void hasCleanup() {
NoopDtor o;
mayThrow(&o);
}
$ clang -S -O2 t.cpp -emit-llvm -o - | grep -A3 -E 'invoke|landingpad'
invoke void @_Z8mayThrowP8NoopDtor(%struct.NoopDtor* nonnull %o)
to label %invoke.cont unwind label %lpad
invoke.cont: ; preds = %entry
call void @llvm.lifetime.end.p0i8(i64 1, i8* nonnull %0) #3
ret void
--
%1 = landingpad { i8*, i32 }
cleanup
call void @llvm.lifetime.end.p0i8(i64 1, i8* nonnull %0) #3
resume { i8*, i32 } %1
In this example, SROA is unable to remove the alloca for `o`, so the
lifetime.end remains in the landingpad cleanup. If we do not escape `o`, some
mid-level pass can remove the landingpad (I'm guessing PruneEH). We should
teach this pass to look past lifetime.end, and other meta instructions (assume,
etc).</pre>
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