Index: llvm/trunk/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
===================================================================
--- llvm/trunk/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
+++ llvm/trunk/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
@@ -96,11 +96,18 @@
   void emitLoadStoreSymbol(MCInst &Inst, unsigned Opcode, SMLoc IDLoc,
                            MCStreamer &Out, bool HasTmpReg);
 
+  // Checks that a PseudoAddTPRel is using x4/tp in its second input operand.
+  // Enforcing this using a restricted register class for the second input
+  // operand of PseudoAddTPRel results in a poor diagnostic due to the fact
+  // 'add' is an overloaded mnemonic.
+  bool checkPseudoAddTPRel(MCInst &Inst, OperandVector &Operands);
+
   /// Helper for processing MC instructions that have been successfully matched
   /// by MatchAndEmitInstruction. Modifications to the emitted instructions,
   /// like the expansion of pseudo instructions (e.g., "li"), can be performed
   /// in this method.
-  bool processInstruction(MCInst &Inst, SMLoc IDLoc, MCStreamer &Out);
+  bool processInstruction(MCInst &Inst, SMLoc IDLoc, OperandVector &Operands,
+                          MCStreamer &Out);
 
 // Auto-generated instruction matching functions
 #define GET_ASSEMBLER_HEADER
@@ -794,7 +801,7 @@
   default:
     break;
   case Match_Success:
-    return processInstruction(Inst, IDLoc, Out);
+    return processInstruction(Inst, IDLoc, Operands, Out);
   case Match_MissingFeature:
     return Error(IDLoc, "instruction use requires an option to be enabled");
   case Match_MnemonicFail:
@@ -1596,7 +1603,21 @@
                     Opcode, IDLoc, Out);
 }
 
+bool RISCVAsmParser::checkPseudoAddTPRel(MCInst &Inst,
+                                         OperandVector &Operands) {
+  assert(Inst.getOpcode() == RISCV::PseudoAddTPRel && "Invalid instruction");
+  assert(Inst.getOperand(2).isReg() && "Unexpected second operand kind");
+  if (Inst.getOperand(2).getReg() != RISCV::X4) {
+    SMLoc ErrorLoc = ((RISCVOperand &)*Operands[3]).getStartLoc();
+    return Error(ErrorLoc, "the second input operand must be tp/x4 when using "
+                           "%tprel_add modifier");
+  }
+
+  return false;
+}
+
 bool RISCVAsmParser::processInstruction(MCInst &Inst, SMLoc IDLoc,
+                                        OperandVector &Operands,
                                         MCStreamer &Out) {
   Inst.setLoc(IDLoc);
 
@@ -1675,6 +1696,9 @@
   case RISCV::PseudoFSD:
     emitLoadStoreSymbol(Inst, RISCV::FSD, IDLoc, Out, /*HasTmpReg=*/true);
     return false;
+  case RISCV::PseudoAddTPRel:
+    if (checkPseudoAddTPRel(Inst, Operands))
+      return true;
   }
 
   emitToStreamer(Out, Inst);
Index: llvm/trunk/test/MC/RISCV/rv32i-invalid.s
===================================================================
--- llvm/trunk/test/MC/RISCV/rv32i-invalid.s
+++ llvm/trunk/test/MC/RISCV/rv32i-invalid.s
@@ -133,6 +133,7 @@
 # TP-relative symbol names require a %tprel_add modifier.
 add a0, a0, tp, zero # CHECK: :[[@LINE]]:17: error: expected '%' for operand modifier
 add a0, a0, tp, %hi(foo) # CHECK: :[[@LINE]]:17: error: operand must be a symbol with %tprel_add modifier
+add a0, tp, a0, %tprel_add(foo) # CHECK: :[[@LINE]]:13: error: the second input operand must be tp/x4 when using %tprel_add modifier
 
 # Unrecognized operand modifier
 addi t0, sp, %modifer(255) # CHECK: :[[@LINE]]:15: error: unrecognized operand modifier