diff --git a/llvm/lib/Target/R600/SIInstrInfo.cpp b/llvm/lib/Target/R600/SIInstrInfo.cpp
index e293c3a22ae8..8eb707d7380f 100644
--- a/llvm/lib/Target/R600/SIInstrInfo.cpp
+++ b/llvm/lib/Target/R600/SIInstrInfo.cpp
@@ -440,7 +440,9 @@ void SIInstrInfo::legalizeOperands(MachineInstr *MI) const {
   // Legalize VOP2
   if (isVOP2(MI->getOpcode()) && Src1Idx != -1) {
     MachineOperand &Src1 = MI->getOperand(Src1Idx);
-    // Legalize VOP2 instructions where src1 is not a VGPR.
+
+    // Legalize VOP2 instructions where src1 is not a VGPR. An SGPR input must
+    // be the first operand, and there can only be one.
     if (Src1.isImm() || Src1.isFPImm() ||
         (Src1.isReg() && RI.isSGPRClass(MRI.getRegClass(Src1.getReg())))) {
       if (MI->isCommutable()) {