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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - instcombine folds branchs on constant conditions to undef"
href="https://bugs.llvm.org/show_bug.cgi?id=33409">33409</a>
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<th>Summary</th>
<td>instcombine folds branchs on constant conditions to undef
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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
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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>davide@freebsd.org
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<th>CC</th>
<td>dberlin@dberlin.org, llvm-bugs@lists.llvm.org, nunoplopes@sapo.pt, regehr@cs.utah.edu, sanjoy@playingwithpointers.com
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<pre>This is something I found out while debugging another MemSSA problem. Not a
proper bug, but something I found surprising.
Given:
@b = external global i32
define void @patatino() {
for.cond:
br i1 true, label %if.end, label %for.inc
if.end: ; preds = %for.cond
%tinkywinky = load i32, i32* @b
br i1 true, label %for.inc, label %for.inc
for.inc: ; preds = %if.end, %if.end,
%for.cond
ret void
}
The terminator in `if.end` after instcombine becomes:
` br i1 undef, label %for.inc, label %for.inc `
IC: Visiting: br i1 true, label %for.inc, label %for.inc
IC: Mod = br i1 true, label %for.inc, label %for.inc
New = br i1 undef, label %for.inc, label %for.inc
This transformation is not useful. Replacing true with undef doesn't really
help anything (SimplifyCFG should be able to fold branches when the condition
is constant).</pre>
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