Add a comment to describe why vector shuffles are legalized to custom DAG nodes.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78884 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 4074fc7..785a7de 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -2439,6 +2439,10 @@
DebugLoc dl = Op.getDebugLoc();
EVT VT = Op.getValueType();
+ // Convert shuffles that are directly supported on NEON to target-specific
+ // DAG nodes, instead of keeping them as shuffles and matching them again
+ // during code selection. This is more efficient and avoids the possibility
+ // of inconsistencies between legalization and selection.
if (SVN->isSplat() && SVN->getSplatIndex() == 0)
return DAG.getNode(ARMISD::VSPLAT0, dl, VT, SVN->getOperand(0));
if (isVREVMask(SVN, 64))