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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - JumpThreading can take take several minutes on large functions"
href="https://bugs.llvm.org/show_bug.cgi?id=37929">37929</a>
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<th>Summary</th>
<td>JumpThreading can take take several minutes on large functions
</td>
</tr>
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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>Linux
</td>
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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
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>vlad@tsyrklevich.net
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<pre>Created <span class=""><a href="attachment.cgi?id=20466" name="attach_20466" title="Reproducer">attachment 20466</a> <a href="attachment.cgi?id=20466&action=edit" title="Reproducer">[details]</a></span>
Reproducer
Filing a bug for this:
<a href="http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180625/563662.html">http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180625/563662.html</a>
The attached file (a preprocessed copy of AArch64InstPrinter.cpp) takes 80s to
compile locally with -O3 [1], and 400s with -O3 + UBSan [2].
The vast majority of that time is spent computing dominator trees for the
JumpThreading pass for two auto-generated functions
(AArch64InstPrinter::printAliasInstr and
AArch64AppleInstPrinter::printAliasInstr) where inlining significantly blows up
the number of basic blocks (from ~5k with -O1 to ~25k with -O3 and ~55k for O3
+ UBSan.) Running CFGSimplication before JumpThreading reduces the # of BBs by
~10k and improves the runtime by ~3x, but the compile for -O3 + UBSan still
takes ~2 minutes. I'm not sure if making that change is justified/sound.
[1] time clang -cc1 -triple x86_64-unknown-linux-gnu -O3 -std=c++11 -emit-llvm
-o /dev/null preprocessed.cpp
[2] time clang -cc1 -triple x86_64-unknown-linux-gnu -O3 -std=c++11 -emit-llvm
-o /dev/null preprocessed.cpp
-fsanitize=alignment,array-bounds,bool,builtin,enum,float-cast-overflow,float-divide-by-zero,integer-divide-by-zero,nonnull-attribute,null,object-size,pointer-overflow,return,returns-nonnull-attribute,shift-base,shift-exponent,signed-integer-overflow,unreachable,vla-bound</pre>
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