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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang mishandles fast-math flags when pragmas are used"
href="https://bugs.llvm.org/show_bug.cgi?id=52563">52563</a>
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<th>Summary</th>
<td>Clang mishandles fast-math flags when pragmas are used
</td>
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
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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
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<th>Component</th>
<td>-New Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>andrew.kaylor@intel.com
</td>
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
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<pre>When pragmas are used that modify the fast-math flags, clang doesn't correctly
apply the changes to all instructions. I've seen this with phi and fneg
instructions. There may be others.
Here are some examples (compiled with -funsafe-math-optimizations, which
applies 'reassoc nsz arcp' outside pragma scopes):
```
#pragma clang fp reassociate(off)
double foo(bool flag, double x, double y) {
return flag ? x : y;
}
```
clang generates a phi instruction with the 'reassoc' flag set.
```
#pragma clang fp reassociate(off)
double bar(double x) {
return foo(x < 0, -x, x);
}
```
Here clang correctly omits the 'reassoc' flag from the fcmp but incorrectly
sets it for the fneg.
```
#pragma clang fp reassociate(off)
void fubar(double x, double *pneg, double *psub) {
*pneg = -x;
*psub = 0.0-x;
}
```
Here clang correctly omits the 'reassoc' flag from the fsub but incorrectly
sets it for the fneg.
The same problem occurs with "pragma float_control"</pre>
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