Index: llvm/trunk/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
===================================================================
--- llvm/trunk/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
+++ llvm/trunk/lib/Target/AMDGPU/AsmParser/AMDGPUAsmParser.cpp
@@ -2657,7 +2657,6 @@
     case AMDGPU::VCC_LO:
     case AMDGPU::VCC_HI:
     case AMDGPU::M0:
-    case AMDGPU::SGPR_NULL:
       return Reg;
     default:
       break;
@@ -2731,9 +2730,13 @@
   const MCOperand &MO = Inst.getOperand(OpIdx);
   if (MO.isImm()) {
     return !isInlineConstant(Inst, OpIdx);
+  } else if (MO.isReg()) {
+    auto Reg = MO.getReg();
+    const MCRegisterInfo *TRI = getContext().getRegisterInfo();
+    return isSGPR(mc2PseudoReg(Reg), TRI) && Reg != SGPR_NULL;
+  } else {
+    return true;
   }
-  return !MO.isReg() ||
-         isSGPR(mc2PseudoReg(MO.getReg()), getContext().getRegisterInfo());
 }
 
 bool AMDGPUAsmParser::validateConstantBusLimitations(const MCInst &Inst) {
Index: llvm/trunk/test/MC/AMDGPU/gfx10-constant-bus.s
===================================================================
--- llvm/trunk/test/MC/AMDGPU/gfx10-constant-bus.s
+++ llvm/trunk/test/MC/AMDGPU/gfx10-constant-bus.s
@@ -55,3 +55,9 @@
 
 v_mad_u64_u32 v[5:6], s12, s1, 0x12345678, 0x12345678
 // GFX10-ERR: error: invalid operand (violates constant bus restrictions)
+
+//-----------------------------------------------------------------------------------------
+// null is free
+
+v_bfe_u32 v5, s1, s2, null
+// GFX10: v_bfe_u32 v5, s1, s2, null      ; encoding: [0x05,0x00,0x48,0xd5,0x01,0x04,0xf4,0x01]