<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [BranchFolding] Investigate reducing the default value of tail-merge-size"
href="https://bugs.llvm.org/show_bug.cgi?id=32802">32802</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[BranchFolding] Investigate reducing the default value of tail-merge-size
</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>Windows NT
</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>Transformation Utilities
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>andrew.v.tischenko@gmail.com, davide@freebsd.org, filcab@gmail.com, jlpaquet@uvic.ca, llvm-bugs@lists.llvm.org, matze@braunis.de
</td>
</tr></table>
<p>
<div>
<pre>llvm\lib\CodeGen\BranchFolding.cpp:
// Heuristic for tail merging (and, inversely, tail duplication).
// TODO: This should be replaced with a target query.
static cl::opt<unsigned>
TailMergeSize("tail-merge-size",
cl::desc("Min number of instructions to consider tail merging"),
cl::init(3), cl::Hidden);
Currently the tail-merge-size for duplicate BB tail merging is set to a default
value of 3 instructions, which prevents us from merging all the BBs that we
could otherwise (<a class="bz_bug_link
bz_status_NEW "
title="NEW - Failure to hoist constant out of loop"
href="show_bug.cgi?id=27136">Bug #27136</a> and D30572). Additionally there appears to be no
testing of this feature at all.
Is the value purely for compile time reasons or does it have to have a value
that must correctly interact with tail-dup-placement-threshold?
Does the TODO comment suggesting making it target specific make sense?</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>