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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Switches with too large ranges check these one after another"
href="http://llvm.org/bugs/show_bug.cgi?id=18349">18349</a>
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<th>Summary</th>
<td>Switches with too large ranges check these one after another
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>3.3
</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>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Common Code Generator Code
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>jn@sirrida.de
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Similar to <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Switches with large ranges may generate excessively large jump tables"
href="show_bug.cgi?id=18348">bug 18348</a> a switch statement with many large ranges are not handled
satisfactorily. In this case I tested large ranges which have more than 64
elements. What I found was that these are tested one after another where a
decision tree would have been much more adequate and as usually happens with
smaller ranges.
As a test case the following program can be compiled with clang -O3 -S:
int main(int argc, char **argv) {
switch (argc) {
case 5000 ... 5064: return 100;
case 5100 ... 5164: return 200;
case 5200 ... 5264: return 300;
case 5300 ... 5364: return 400;
case 5400 ... 5464: return 500;
case 5500 ... 5564: return 600;
default: return -1;
}
}
The special case for ranges with more than 64 elements seems to artificial as
is also discussed in <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Should enhance LLVM switch instruction to take case ranges"
href="show_bug.cgi?id=1255">bug #1255</a>.
Also, the 64 ought to be configurable with a switch (if necessary at all).
The offending code of 3.3 can be found in lib/CodeGen/CGStmt.cpp; I could not
locate it in trunk (currently 3.4 RC3), however this version compiles to the
same result.</pre>
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