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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - LICM seems unnecessarily slow"
href="https://llvm.org/bugs/show_bug.cgi?id=23077">23077</a>
</td>
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<tr>
<th>Summary</th>
<td>LICM seems unnecessarily slow
</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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>tobias@grosser.es
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=14121" name="attach_14121" title="Test case">attachment 14121</a> <a href="attachment.cgi?id=14121&action=edit" title="Test case">[details]</a></span>
Test case
This simple file takes with 'opt -basicaa -licm out.opt.ll' 130ms to run. This
is suprisingly slow.
If I comment out the following lines:
// If there are any call sites in the alias set, add them to this AST.
- for (unsigned i = 0, e = AS.UnknownInsts.size(); i != e; ++i)
- add(AS.UnknownInsts[i]);
+ //for (unsigned i = 0, e = AS.UnknownInsts.size(); i != e; ++i)
+ // add(AS.UnknownInsts[i]);
Compile time is reduced to 20ms.
Surisingly only a single test case fails:
Transforms/LICM/PR21582.ll
I do not yet understand well what these Unknown instructions are suppose to be
used for, but I somehow have the feeling there is an obvious inefficiency here.
If I dump the AST:
+++ b/lib/Transforms/Scalar/LICM.cpp
@@ -200,6 +200,7 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
delete InnerAST;
LoopToAliasSetMap.erase(InnerL);
}
+ CurAST->dump();
I get(after some delay) the following output:
Alias Set Tracker: 128 alias sets for 0 pointer values.
AliasSet[0x454de10, 1] may alias, Mod/Ref
1 Unknown instructions: void <badref>
AliasSet[0x454de60, 1] may alias, Mod/Ref
1 Unknown instructions: void <badref>
AliasSet[0x454deb0, 1] may alias, Mod/Ref
1 Unknown instructions: void <badref>
AliasSet[0x454df20, 1] may alias, Mod/Ref
1 Unknown instructions: void <badref>
AliasSet[0x454df90, 1] may alias, Mod/Ref
1 Unknown instructions: void <badref>
AliasSet[0x454e000, 1] may alias, Mod/Ref
1 Unknown instructions: void <badref>
...
Do we really need 128 alias sets here?</pre>
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