[PATCH] Lower certain build_vectors to insertps instructions

[Elena Demikhovsky]

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Comment at: lib/Target/X86/X86ISelLowering.cpp:5462
@@ +5461,3 @@
+        ElementMoveMask | (~NonZeros & 0xf));
+    return DAG.getNode(X86ISD::INSERTPS, dl, VT, V, V, InsertpsMask);
+  }
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Let's assume that the first element of the BUILD_VECTOR is "undef" and the first element of EXTRACT does not go to any place. FirstNonZeroIdx = 2, for example. The INSERTPS instruction you use copies the first element to another place, because this instruction can manipulate with the first element only.

http://reviews.llvm.org/D3521