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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 - LowerSwitch should remove all dead blocks introduced by switch processing"
href="https://bugs.llvm.org/show_bug.cgi?id=52383">52383</a>
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<th>Summary</th>
<td>LowerSwitch should remove all dead blocks introduced by switch processing
</td>
</tr>
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<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>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Transformation Utilities
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>yilong.guo@intel.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Consider the following ll:
```
define i32 @f(i32 %c) {
chk65:
%cmp = icmp sgt i32 %c, 65
br i1 %cmp, label %return, label %chk0
chk0:
%cmp1 = icmp slt i32 %c, 0
br i1 %cmp, label %return, label %bb_if
bb_if:
%ashr.val = ashr exact i32 %c, 2
%cmp2 = icmp sgt i32 %ashr.val, 14
br i1 %cmp2, label %bb_switch, label %return
bb_switch:
; %ashr.val must be 15 or 16 here (analyzed by LazyValueInfo)
switch i32 %ashr.val, label %out_of_switch_range [
i32 15, label %return
i32 16, label %another_ret
]
; unreachable default case
out_of_switch_range:
br label %successor_of_unreachable
; unreachable successors
successor_of_unreachable:
br label %return
another_ret:
br label %return
return:
%retval = phi i32 [-1, %chk0], [-1, %chk65], [-1, %bb_if], [42, %bb_switch],
[42, %another_ret], [-42, %successor_of_unreachable]
ret i32 %retval
}
```
Both "out_of_switch_range" and "successor_of_unreachable" should be deleted as
they become dead after switch lowering.
But LowerSwitch only deletes the "out_of_switch_range" -- it didn't delete dead
block's dominatees which also become unreachable.</pre>
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