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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - FMF.isFast() returns incorrect result when FMF==0x7f"
href="https://bugs.llvm.org/show_bug.cgi?id=49896">49896</a>
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<th>Summary</th>
<td>FMF.isFast() returns incorrect result when FMF==0x7f
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<th>Product</th>
<td>new-bugs
</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>Windows NT
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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
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<th>Component</th>
<td>new bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>melanie.blower@intel.com
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>I want to check whether the IR Builder FMF flags are set to isFast() in
clang/codegen
I have a test case that selects all the FMF flags on the cc1 command line,
I tried to write this code:
auto FMF = Builder.getFastMathFlags();
if (FMF.isFast())
but that didn't work, I had to write like this:
if (FMF.allowReassoc() && FMF.noNaNs() && FMF.noInfs() &&
FMF.noSignedZeros() && FMF.allowReciprocal() && FMF.allowContract() &&
FMF.approxFunc())
That's because the implementation of isFast ultimately checks, in llvm
Operator.h, if the byte == ~0
OK to rewrite that check as byte == 0x7f? I read a comment that the bits in
the struct are all used up, there's no 8th bit available at this time.
I don't have an easy reproducer, the patch I'm working on is
<a href="https://reviews.llvm.org/D100118">https://reviews.llvm.org/D100118</a> ; the line where I had to check each bits is
CGBuiltin.cpp:3829 in that patch. If I change it to isFast() then the first run
line in the test case fails, clang/test/CodeGen/arithmetic-fence-builtin.c</pre>
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