I don't quite understand this. Does combining come through lowerVectorShuffle? Or when would a VECTOR_SHUFFLE come through where this wasn't true?<span></span><br><br>On Sunday, August 7, 2016, Simon Pilgrim via llvm-commits <<a href="mailto:llvm-commits@lists.llvm.org">llvm-commits@lists.llvm.org</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: rksimon<br>
Date: Sun Aug  7 10:29:12 2016<br>
New Revision: 277959<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=277959&view=rev" target="_blank">http://llvm.org/viewvc/llvm-<wbr>project?rev=277959&view=rev</a><br>
Log:<br>
[X86] lowerVectorShuffle - ensure that undefined mask elements only use SM_SentinelUndef<br>
<br>
Help lowering and combining (which can specify SM_SentinelZero mask elements) share more shuffle matching code.<br>
<br>
Modified:<br>
    llvm/trunk/lib/Target/X86/<wbr>X86ISelLowering.cpp<br>
<br>
Modified: llvm/trunk/lib/Target/X86/<wbr>X86ISelLowering.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=277959&r1=277958&r2=277959&view=diff" target="_blank">http://llvm.org/viewvc/llvm-<wbr>project/llvm/trunk/lib/Target/<wbr>X86/X86ISelLowering.cpp?rev=<wbr>277959&r1=277958&r2=277959&<wbr>view=diff</a><br>
==============================<wbr>==============================<wbr>==================<br>
--- llvm/trunk/lib/Target/X86/<wbr>X86ISelLowering.cpp (original)<br>
+++ llvm/trunk/lib/Target/X86/<wbr>X86ISelLowering.cpp Sun Aug  7 10:29:12 2016<br>
@@ -12281,6 +12281,15 @@ static SDValue lowerVectorShuffle(SDValu<br>
         return DAG.getVectorShuffle(VT, DL, V1, V2, NewMask);<br>
       }<br>
<br>
+  // Ensure that undefined mask elements only use SM_SentinelUndef.<br>
+  if (llvm::any_of(Mask, [](int M) { return M < SM_SentinelUndef; })) {<br>
+    SmallVector<int, 8> NewMask(Mask.begin(), Mask.end());<br>
+    for (int &M : NewMask)<br>
+      if (M < SM_SentinelUndef)<br>
+        M = SM_SentinelUndef;<br>
+    return DAG.getVectorShuffle(VT, DL, V1, V2, NewMask);<br>
+  }<br>
+<br>
   // We actually see shuffles that are entirely re-arrangements of a set of<br>
   // zero inputs. This mostly happens while decomposing complex shuffles into<br>
   // simple ones. Directly lower these as a buildvector of zeros.<br>
<br>
<br>
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</blockquote><br><br>-- <br>~Craig<br>