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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86] Failure to prevent schedule across x87 control word instructions"
href="https://bugs.llvm.org/show_bug.cgi?id=34454">34454</a>
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<th>Summary</th>
<td>[X86] Failure to prevent schedule across x87 control word instructions
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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>Windows NT
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<th>Status</th>
<td>NEW
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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>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
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<th>CC</th>
<td>craig.topper@gmail.com, emaste@freebsd.org, gadi.haber@intel.com, llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com
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<pre>Branched off from [<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - After r307529, sinl() test failures in FreeBSD's libm"
href="show_bug.cgi?id=34080">Bug #34080</a>].
The partial SandyBridge schedule model (which is used for all default x86-64
targets) resulted in the scheduler moving some instructions across fldcw/fnstcw
instructions, affecting rounding of truncated stores etc.
The issue appears to be that we're incorrectly handling the control word
register dependency, which is odd because it looks like fldcw/fnstcw are
correctly flagged to cause side effects.
It could also be a chain issue in the fptosi store code in
X86TargetLowering::EmitInstrWithCustomInserter but I didn't notice anything.
Exposing this is tricky, and seems to involve applying rL307529 but not
rL310792.</pre>
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