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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 - Long compile time in MachineCSE profitability checks."
href="https://bugs.llvm.org/show_bug.cgi?id=37277">37277</a>
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<th>Summary</th>
<td>Long compile time in MachineCSE profitability checks.
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<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>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Common Code Generator Code
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>huihuiz@codeaurora.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>We have a reduced test case that shows LLVM pass "Machine Common Subexpression
Elimination" is taking a long while, especially in function
isProfitableToCSE().
In the reduced test case, test.ll, we observed that 82.6% out of total compile
time 46.6 seconds is spent on MachineCSE. And most of the time is spent on the
profitability checks.
There are a lot of repetition in the implementation of isProtitableToCSE(),
e.g., repetitively scanning through the use instruction of Reg and CSReg.
run commands:
llc test.ll -o /tmp/output
with time report
llc -time-passes test.ll -o /tmp/output
===-------------------------------------------------------------------------===
... Pass execution timing report ...
===-------------------------------------------------------------------------===
Total Execution Time: 46.6000 seconds (46.6320 wall clock)
---User Time--- --System Time-- --User+System-- ---Wall Time--- ---
Name ---
38.2800 ( 82.6%) 0.0760 ( 32.8%) 38.3560 ( 82.3%) 38.3652 ( 82.3%)
Machine Common Subexpression Elimination
2.3800 ( 5.1%) 0.1200 ( 51.7%) 2.5000 ( 5.4%) 2.5276 ( 5.4%) ARM
Instruction Selection
1.2160 ( 2.6%) 0.0000 ( 0.0%) 1.2160 ( 2.6%) 1.2168 ( 2.6%)
Simple Register Coalescing
0.7440 ( 1.6%) 0.0040 ( 1.7%) 0.7480 ( 1.6%) 0.7480 ( 1.6%)
Greedy Register Allocator
0.6040 ( 1.3%) 0.0040 ( 1.7%) 0.6080 ( 1.3%) 0.6129 ( 1.3%) Live
Variable Analysis
0.5680 ( 1.2%) 0.0000 ( 0.0%) 0.5680 ( 1.2%) 0.5698 ( 1.2%) ARM
constant island placement and branch shortening pass
0.4000 ( 0.9%) 0.0000 ( 0.0%) 0.4000 ( 0.9%) 0.4016 ( 0.9%)
Control Flow Optimizer
0.3160 ( 0.7%) 0.0000 ( 0.0%) 0.3160 ( 0.7%) 0.3162 ( 0.7%) If
Converter
0.2360 ( 0.5%) 0.0040 ( 1.7%) 0.2400 ( 0.5%) 0.2377 ( 0.5%) Live
Interval Analysis
0.2360 ( 0.5%) 0.0000 ( 0.0%) 0.2360 ( 0.5%) 0.2324 ( 0.5%)
Branch Probability Basic Block Placement
0.1720 ( 0.4%) 0.0000 ( 0.0%) 0.1720 ( 0.4%) 0.1708 ( 0.4%) Post
RA top-down list latency scheduler
0.0920 ( 0.2%) 0.0000 ( 0.0%) 0.0920 ( 0.2%) 0.0897 ( 0.2%)
Machine code sinking
0.0720 ( 0.2%) 0.0080 ( 3.4%) 0.0800 ( 0.2%) 0.0818 ( 0.2%) ARM
Assembly Printer
0.0720 ( 0.2%) 0.0040 ( 1.7%) 0.0760 ( 0.2%) 0.0721 ( 0.2%)
ReachingDefAnalysis
0.0640 ( 0.1%) 0.0000 ( 0.0%) 0.0640 ( 0.1%) 0.0617 ( 0.1%)
CodeGen Prepare
0.0600 ( 0.1%) 0.0000 ( 0.0%) 0.0600 ( 0.1%) 0.0616 ( 0.1%)
Simplify the CFG</pre>
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