[Diagnostics][Inline-Asm]Allow targets to provide elaborations regarding failures resulted from (GNU-inline-asm) modifiers' apply

[coby]

Summary

Currently, when a machine-dependent GNU-inline-asm modifier cannot be applied due to whatever error - a rather general error message is emitted.
This patch provides infrastructure for a target to supply a more detailed diagnostics regarding such a failure.
As a result - diagnostics for the case where X86's 'H' modifier apply is erroneous is added, which aligns Clang's diagnostics with GCC.

[coby]

Please add whatever reviewers you see as fit :)
thx

[fedor.sergeev]

Any tests checking new diagnostics?

[coby]

In D35890#821498, @fedor.sergeev wrote:

Any tests checking new diagnostics?

blimey
forgot to add it, thanks for mentioning it, will upload right away

[coby]

Added forgotten test

[coby]

anyone?

[arsenm]

lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp

275–276

I would expect this does the right thing anyway if you just << ErrorMsg even when empty

[coby]

lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp

275–276

You right, thx.
will update

include/llvm/CodeGen/AsmPrinter.h

public:
   /// bits of target-specific knowledge into the asmstrings.  The syntax used is
   /// ${:comment}.  Targets can override this to add support for their own
   /// strange codes.
   virtual void PrintSpecial(const MachineInstr *MI, raw_ostream &OS,
                             const char *Code) const;
 
   /// Print the specified operand of MI, an INLINEASM instruction, using the
   /// specified assembler variant.  Targets should override this to format as
-  /// appropriate.  This method can return true if the operand is erroneous.
+  /// appropriate.  This method can return true if the operand is erroneous,
+  /// and may supply some diagnostics via ErrorMsg
   virtual bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                unsigned AsmVariant, const char *ExtraCode,
-                               raw_ostream &OS);
+                               raw_ostream &OS, StringRef &ErrorMsg);
 
   /// Print the specified operand of MI, an INLINEASM instruction, using the
   /// specified assembler variant as an address. Targets should override this to
   /// format as appropriate.  This method can return true if the operand is
   /// erroneous.
   virtual bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                                      unsigned AsmVariant, const char *ExtraCode,
                                      raw_ostream &OS);

lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp

case '$': {
 
       // Scan to find the machine operand number for the operand.
       for (; Val; --Val) {
         if (OpNo >= MI->getNumOperands()) break;
         unsigned OpFlags = MI->getOperand(OpNo).getImm();
         OpNo += InlineAsm::getNumOperandRegisters(OpFlags) + 1;
       }
 
+      // Dedicate an Error Message container for target provided diagnostics
+      StringRef ErrorMsg;
+
       // We may have a location metadata attached to the end of the
       // instruction, and at no point should see metadata at any
       // other point while processing. It's an error if so.
       if (OpNo >= MI->getNumOperands() ||
           MI->getOperand(OpNo).isMetadata()) {
         Error = true;
       } else {
         unsigned OpFlags = MI->getOperand(OpNo).getImm();
         ++OpNo;  // Skip over the ID number.
 
         if (InlineAsm::isMemKind(OpFlags)) {
           Error = AP->PrintAsmMemoryOperand(MI, OpNo, InlineAsmVariant,
                                             /*Modifier*/ nullptr, OS);
         } else {
           Error = AP->PrintAsmOperand(MI, OpNo, InlineAsmVariant,
-                                      /*Modifier*/ nullptr, OS);
+                                      /*Modifier*/ nullptr, OS,
+                                      ErrorMsg);
         }
       }
       if (Error) {
         std::string msg;
         raw_string_ostream Msg(msg);
         Msg << "invalid operand in inline asm: '" << AsmStr << "'";
+        if (!ErrorMsg.empty())
+          Msg << ErrorMsg;
         MMI->getModule()->getContext().emitError(LocCookie, Msg.str());
       }
       break;
     }
     }
   }
   OS << "\n\t.att_syntax\n" << (char)0;  // null terminate string.
 }
case '$': {
 
         // Scan to find the machine operand number for the operand.
         for (; Val; --Val) {
           if (OpNo >= MI->getNumOperands()) break;
           unsigned OpFlags = MI->getOperand(OpNo).getImm();
           OpNo += InlineAsm::getNumOperandRegisters(OpFlags) + 1;
         }
 
+        // Dedicate an Error Message container for target provided diagnostics
+        StringRef ErrorMsg;
+
         // We may have a location metadata attached to the end of the
         // instruction, and at no point should see metadata at any
         // other point while processing. It's an error if so.
         if (OpNo >= MI->getNumOperands() ||
             MI->getOperand(OpNo).isMetadata()) {
           Error = true;
         } else {
           unsigned OpFlags = MI->getOperand(OpNo).getImm();
           ++OpNo;  // Skip over the ID number.
 
           if (Modifier[0] == 'l') { // Labels are target independent.
             // FIXME: What if the operand isn't an MBB, report error?
             const MCSymbol *Sym = MI->getOperand(OpNo).getMBB()->getSymbol();
             Sym->print(OS, AP->MAI);
           } else {
             if (InlineAsm::isMemKind(OpFlags)) {
               Error = AP->PrintAsmMemoryOperand(MI, OpNo, InlineAsmVariant,
                                                 Modifier[0] ? Modifier : nullptr,
                                                 OS);
             } else {
               Error = AP->PrintAsmOperand(MI, OpNo, InlineAsmVariant,
-                                          Modifier[0] ? Modifier : nullptr, OS);
+                                          Modifier[0] ? Modifier : nullptr, OS,
+                                          ErrorMsg);
             }
           }
         }
         if (Error) {
           std::string msg;
           raw_string_ostream Msg(msg);
-          Msg << "invalid operand in inline asm: '" << AsmStr << "'";
+          Msg << (!ErrorMsg.empty() ? ErrorMsg :
+                  "invalid operand in inline asm: ");
+          Msg << "'" << AsmStr << "'";
           MMI->getModule()->getContext().emitError(LocCookie, Msg.str());
         }
       }
       break;
     }
     }
   }
   OS << '\n' << (char)0;  // null terminate string.
void AsmPrinter::PrintSpecial(const MachineInstr *MI, raw_ostream &OS,
   }
 }
 
 /// PrintAsmOperand - Print the specified operand of MI, an INLINEASM
 /// instruction, using the specified assembler variant.  Targets should
 /// override this to format as appropriate.
 bool AsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                  unsigned AsmVariant, const char *ExtraCode,
-                                 raw_ostream &O) {
+                                 raw_ostream &O, StringRef &ErrMsg) {
   // Does this asm operand have a single letter operand modifier?
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0) return true; // Unknown modifier.
 
     const MachineOperand &MO = MI->getOperand(OpNo);
     switch (ExtraCode[0]) {
     default:
       return true;  // Unknown modifier.

lib/Target/AArch64/AArch64AsmPrinter.cpp

private:
   void printOperand(const MachineInstr *MI, unsigned OpNum, raw_ostream &O);
   bool printAsmMRegister(const MachineOperand &MO, char Mode, raw_ostream &O);
   bool printAsmRegInClass(const MachineOperand &MO,
                           const TargetRegisterClass *RC, bool isVector,
                           raw_ostream &O);
 
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
                        unsigned AsmVariant, const char *ExtraCode,
-                       raw_ostream &O) override;
+                       raw_ostream &O, StringRef &ErrorMsg) override;
   bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNum,
                              unsigned AsmVariant, const char *ExtraCode,
                              raw_ostream &O) override;
 
   void PrintDebugValueComment(const MachineInstr *MI, raw_ostream &OS);
 
   void EmitFunctionBodyEnd() override;
 
bool AArch64AsmPrinter::printAsmRegInClass(const MachineOperand &MO,
   assert(RI->regsOverlap(RegToPrint, Reg));
   O << AArch64InstPrinter::getRegisterName(
            RegToPrint, isVector ? AArch64::vreg : AArch64::NoRegAltName);
   return false;
 }
 
 bool AArch64AsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
                                         unsigned AsmVariant,
-                                        const char *ExtraCode, raw_ostream &O) {
+                                        const char *ExtraCode, raw_ostream &O,
+                                        StringRef &ErrorMsg) {
   const MachineOperand &MO = MI->getOperand(OpNum);
 
   // First try the generic code, which knows about modifiers like 'c' and 'n'.
-  if (!AsmPrinter::PrintAsmOperand(MI, OpNum, AsmVariant, ExtraCode, O))
+  if (!AsmPrinter::PrintAsmOperand(MI, OpNum, AsmVariant, ExtraCode, O, ErrorMsg))
     return false;
 
   // Does this asm operand have a single letter operand modifier?
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0)
       return true; // Unknown modifier.
 
     switch (ExtraCode[0]) {

lib/Target/AMDGPU/AMDGPUAsmPrinter.h

public:
 
   void EmitEndOfAsmFile(Module &M) override;
 
   bool isBlockOnlyReachableByFallthrough(
     const MachineBasicBlock *MBB) const override;
 
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        unsigned AsmVariant, const char *ExtraCode,
-                       raw_ostream &O) override;
+                       raw_ostream &O, StringRef &ErrorMsg) override;
 
 protected:
   std::vector<std::string> DisasmLines, HexLines;
   size_t DisasmLineMaxLen;
   AMDGPUAS AMDGPUASI;
 };
 
 } // end namespace llvm
 
 #endif // LLVM_LIB_TARGET_AMDGPU_AMDGPUASMPRINTER_H

lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp

Out.debug_wavefront_private_segment_offset_sgpr =
       CurrentProgramInfo.DebuggerWavefrontPrivateSegmentOffsetSGPR;
     Out.debug_private_segment_buffer_sgpr =
       CurrentProgramInfo.DebuggerPrivateSegmentBufferSGPR;
   }
 }
 
 bool AMDGPUAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                        unsigned AsmVariant,
-                                       const char *ExtraCode, raw_ostream &O) {
+                                       const char *ExtraCode, raw_ostream &O,
+                                       StringRef &ErrorMsg) {
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0)
       return true; // Unknown modifier.
 
     switch (ExtraCode[0]) {
     default:
       // See if this is a generic print operand
-      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O);
+      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O,
+                                         ErrorMsg);
     case 'r':
       break;
     }
   }
 
   AMDGPUInstPrinter::printRegOperand(MI->getOperand(OpNo).getReg(), O,
                    *TM.getSubtargetImpl(*MF->getFunction())->getRegisterInfo());
   return false;
 }

lib/Target/ARM/ARMAsmPrinter.h

public:
   StringRef getPassName() const override {
     return "ARM Assembly Printer";
   }
 
   void printOperand(const MachineInstr *MI, int OpNum, raw_ostream &O);
 
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
                        unsigned AsmVariant, const char *ExtraCode,
-                       raw_ostream &O) override;
+                       raw_ostream &O, StringRef &ErrorMsg) override;
   bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNum,
                              unsigned AsmVariant, const char *ExtraCode,
                              raw_ostream &O) override;
 
   void emitInlineAsmEnd(const MCSubtargetInfo &StartInfo,
                         const MCSubtargetInfo *EndInfo) const override;
 
   void EmitJumpTableAddrs(const MachineInstr *MI);

lib/Target/ARM/ARMAsmPrinter.cpp

GetARMJTIPICJumpTableLabel(unsigned uid) const {
   SmallString<60> Name;
   raw_svector_ostream(Name) << DL.getPrivateGlobalPrefix() << "JTI"
                             << getFunctionNumber() << '_' << uid;
   return OutContext.getOrCreateSymbol(Name);
 }
 
 bool ARMAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
                                     unsigned AsmVariant, const char *ExtraCode,
-                                    raw_ostream &O) {
+                                    raw_ostream &O, StringRef &ErrorMsg) {
   // Does this asm operand have a single letter operand modifier?
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0) return true; // Unknown modifier.
 
     switch (ExtraCode[0]) {
     default:
       // See if this is a generic print operand
-      return AsmPrinter::PrintAsmOperand(MI, OpNum, AsmVariant, ExtraCode, O);
+      return AsmPrinter::PrintAsmOperand(MI, OpNum, AsmVariant, ExtraCode, O,
+                                         ErrorMsg);
     case 'a': // Print as a memory address.
       if (MI->getOperand(OpNum).isReg()) {
         O << "["
           << ARMInstPrinter::getRegisterName(MI->getOperand(OpNum).getReg())
           << "]";
         return false;
       }
       LLVM_FALLTHROUGH;

lib/Target/Hexagon/HexagonAsmPrinter.h

public:
 
     void HexagonProcessInstruction(MCInst &Inst,
                                    const MachineInstr &MBB);
 
 
     void printOperand(const MachineInstr *MI, unsigned OpNo, raw_ostream &O);
     bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                          unsigned AsmVariant, const char *ExtraCode,
-                         raw_ostream &OS) override;
+                         raw_ostream &OS, StringRef &ErrorMsg) override;
     bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                                unsigned AsmVariant, const char *ExtraCode,
                                raw_ostream &OS) override;
 
     static const char *getRegisterName(unsigned RegNo);
   };
 
 } // end of llvm namespace
 
 #endif

lib/Target/Hexagon/HexagonAsmPrinter.cpp

 }
 
 
 /// PrintAsmOperand - Print out an operand for an inline asm expression.
 ///
 bool HexagonAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                         unsigned AsmVariant,
                                         const char *ExtraCode,
-                                        raw_ostream &OS) {
+                                        raw_ostream &OS,
+                                        StringRef &ErrorMsg) {
   // Does this asm operand have a single letter operand modifier?
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0)
       return true; // Unknown modifier.
 
     switch (ExtraCode[0]) {
     default:
       // See if this is a generic print operand
-      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, OS);
+      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, OS,
+                                         ErrorMsg);
     case 'c': // Don't print "$" before a global var name or constant.
       // Hexagon never has a prefix.
       printOperand(MI, OpNo, OS);
       return false;
     case 'L':
     case 'H': { // The highest-numbered register of a pair.
       const MachineOperand &MO = MI->getOperand(OpNo);
       const MachineFunction &MF = *MI->getParent()->getParent();

lib/Target/Lanai/LanaiAsmPrinter.cpp

explicit LanaiAsmPrinter(TargetMachine &TM,
                            std::unique_ptr<MCStreamer> Streamer)
       : AsmPrinter(TM, std::move(Streamer)) {}
 
   StringRef getPassName() const override { return "Lanai Assembly Printer"; }
 
   void printOperand(const MachineInstr *MI, int OpNum, raw_ostream &O);
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        unsigned AsmVariant, const char *ExtraCode,
-                       raw_ostream &O) override;
+                       raw_ostream &O, StringRef &ErrorMsg) override;
   void EmitInstruction(const MachineInstr *MI) override;
   bool isBlockOnlyReachableByFallthrough(
       const MachineBasicBlock *MBB) const override;
 
 private:
   void customEmitInstruction(const MachineInstr *MI);
   void emitCallInstruction(const MachineInstr *MI);
 };
void LanaiAsmPrinter::printOperand(const MachineInstr *MI, int OpNum,
   default:
     llvm_unreachable("<unknown operand type>");
   }
 }
 
 // PrintAsmOperand - Print out an operand for an inline asm expression.
 bool LanaiAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                       unsigned /*AsmVariant*/,
-                                      const char *ExtraCode, raw_ostream &O) {
+                                      const char *ExtraCode, raw_ostream &O,
+                                      StringRef &ErrorMsg) {
   // Does this asm operand have a single letter operand modifier?
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1])
       return true; // Unknown modifier.
 
     switch (ExtraCode[0]) {
     // The highest-numbered register of a pair.
     case 'H': {

lib/Target/MSP430/MSP430AsmPrinter.cpp

public:
     StringRef getPassName() const override { return "MSP430 Assembly Printer"; }
 
     void printOperand(const MachineInstr *MI, int OpNum,
                       raw_ostream &O, const char* Modifier = nullptr);
     void printSrcMemOperand(const MachineInstr *MI, int OpNum,
                             raw_ostream &O);
     bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                          unsigned AsmVariant, const char *ExtraCode,
-                         raw_ostream &O) override;
+                         raw_ostream &O,
+                         StringRef &ErrorMsg) override;
     bool PrintAsmMemoryOperand(const MachineInstr *MI,
                                unsigned OpNo, unsigned AsmVariant,
                                const char *ExtraCode, raw_ostream &O) override;
     void EmitInstruction(const MachineInstr *MI) override;
   };
 } // end of anonymous namespace
 
 
if (Base.getReg()) {
     O << ')';
   }
 }
 
 /// PrintAsmOperand - Print out an operand for an inline asm expression.
 ///
 bool MSP430AsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                        unsigned AsmVariant,
-                                       const char *ExtraCode, raw_ostream &O) {
+                                       const char *ExtraCode, raw_ostream &O,
+                                       StringRef &ErrorMsg) {
   // Does this asm operand have a single letter operand modifier?
   if (ExtraCode && ExtraCode[0])
     return true; // Unknown modifier.
 
   printOperand(MI, OpNo, O);
   return false;
 }
 

lib/Target/Mips/MipsAsmPrinter.h

public:
   void EmitFunctionEntryLabel() override;
   void EmitFunctionBodyStart() override;
   void EmitFunctionBodyEnd() override;
   void EmitBasicBlockEnd(const MachineBasicBlock &MBB) override;
   bool isBlockOnlyReachableByFallthrough(
                                    const MachineBasicBlock* MBB) const override;
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        unsigned AsmVariant, const char *ExtraCode,
-                       raw_ostream &O) override;
+                       raw_ostream &O, StringRef &ErrorMsg) override;
   bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNum,
                              unsigned AsmVariant, const char *ExtraCode,
                              raw_ostream &O) override;
   void printOperand(const MachineInstr *MI, int opNum, raw_ostream &O);
   void printMemOperand(const MachineInstr *MI, int opNum, raw_ostream &O);
   void printMemOperandEA(const MachineInstr *MI, int opNum, raw_ostream &O);
   void printFCCOperand(const MachineInstr *MI, int opNum, raw_ostream &O,
                        const char *Modifier = nullptr);

lib/Target/Mips/MipsAsmPrinter.cpp

bool MipsAsmPrinter::isBlockOnlyReachableByFallthrough(const MachineBasicBlock*
   while (I != Pred->begin() && !(--I)->isTerminator()) ;
 
   return !I->isBarrier();
 }
 
 // Print out an operand for an inline asm expression.
 bool MipsAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
                                      unsigned AsmVariant, const char *ExtraCode,
-                                     raw_ostream &O) {
+                                     raw_ostream &O, StringRef &ErrorMsg) {
   // Does this asm operand have a single letter operand modifier?
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0) return true; // Unknown modifier.
 
     const MachineOperand &MO = MI->getOperand(OpNum);
     switch (ExtraCode[0]) {
     default:
       // See if this is a generic print operand
-      return AsmPrinter::PrintAsmOperand(MI,OpNum,AsmVariant,ExtraCode,O);
+      return AsmPrinter::PrintAsmOperand(MI,OpNum,AsmVariant,ExtraCode,O,
+                                         ErrorMsg);
     case 'X': // hex const int
       if ((MO.getType()) != MachineOperand::MO_Immediate)
         return true;
       O << "0x" << Twine::utohexstr(MO.getImm());
       return false;
     case 'x': // hex const int (low 16 bits)
       if ((MO.getType()) != MachineOperand::MO_Immediate)
         return true;

lib/Target/NVPTX/NVPTXAsmPrinter.h

private:
   void emitVirtualRegister(unsigned int vr, raw_ostream &);
   void emitFunctionParamList(const Function *, raw_ostream &O);
   void emitFunctionParamList(const MachineFunction &MF, raw_ostream &O);
   void setAndEmitFunctionVirtualRegisters(const MachineFunction &MF);
   void printReturnValStr(const Function *, raw_ostream &O);
   void printReturnValStr(const MachineFunction &MF, raw_ostream &O);
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        unsigned AsmVariant, const char *ExtraCode,
-                       raw_ostream &) override;
+                       raw_ostream &, StringRef &ErrorMsg) override;
   void printOperand(const MachineInstr *MI, int opNum, raw_ostream &O,
                     const char *Modifier = nullptr);
   bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                              unsigned AsmVariant, const char *ExtraCode,
                              raw_ostream &) override;
 
   const MCExpr *lowerConstantForGV(const Constant *CV, bool ProcessingGeneric);
   void printMCExpr(const MCExpr &Expr, raw_ostream &OS);

lib/Target/NVPTX/NVPTXAsmPrinter.cpp

void NVPTXAsmPrinter::printMCExpr(const MCExpr &Expr, raw_ostream &OS) {
 
   llvm_unreachable("Invalid expression kind!");
 }
 
 /// PrintAsmOperand - Print out an operand for an inline asm expression.
 ///
 bool NVPTXAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                       unsigned AsmVariant,
-                                      const char *ExtraCode, raw_ostream &O) {
+                                      const char *ExtraCode, raw_ostream &O,
+                                      StringRef &ErrorMsg) {
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0)
       return true; // Unknown modifier.
 
     switch (ExtraCode[0]) {
     default:
       // See if this is a generic print operand
-      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O);
+      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O,
+                                         ErrorMsg);
     case 'r':
       break;
     }
   }
 
   printOperand(MI, OpNo, O);
 
   return false;

lib/Target/PowerPC/PPCAsmPrinter.cpp

public:
   }
 
     void EmitInstruction(const MachineInstr *MI) override;
 
     void printOperand(const MachineInstr *MI, unsigned OpNo, raw_ostream &O);
 
     bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                          unsigned AsmVariant, const char *ExtraCode,
-                         raw_ostream &O) override;
+                         raw_ostream &O, StringRef &ErrorMsg) override;
     bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                                unsigned AsmVariant, const char *ExtraCode,
                                raw_ostream &O) override;
 
     void EmitEndOfAsmFile(Module &M) override;
 
     void LowerSTACKMAP(StackMaps &SM, const MachineInstr &MI);
     void LowerPATCHPOINT(StackMaps &SM, const MachineInstr &MI);
default:
     return;
   }
 }
 
 /// PrintAsmOperand - Print out an operand for an inline asm expression.
 ///
 bool PPCAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                     unsigned AsmVariant,
-                                    const char *ExtraCode, raw_ostream &O) {
+                                    const char *ExtraCode, raw_ostream &O,
+                                    StringRef &ErrorMsg) {
   // Does this asm operand have a single letter operand modifier?
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0) return true; // Unknown modifier.
 
     switch (ExtraCode[0]) {
     default:
       // See if this is a generic print operand
-      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O);
+      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O,
+                                         ErrorMsg);
     case 'c': // Don't print "$" before a global var name or constant.
       break; // PPC never has a prefix.
     case 'L': // Write second word of DImode reference.
       // Verify that this operand has two consecutive registers.
       if (!MI->getOperand(OpNo).isReg() ||
           OpNo+1 == MI->getNumOperands() ||
           !MI->getOperand(OpNo+1).isReg())
         return true;

lib/Target/Sparc/SparcAsmPrinter.cpp

public:
     void EmitInstruction(const MachineInstr *MI) override;
 
     static const char *getRegisterName(unsigned RegNo) {
       return SparcInstPrinter::getRegisterName(RegNo);
     }
 
     bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                          unsigned AsmVariant, const char *ExtraCode,
-                         raw_ostream &O) override;
+                         raw_ostream &O, StringRef &ErrorMsg) override;
     bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                                unsigned AsmVariant, const char *ExtraCode,
                                raw_ostream &O) override;
 
     void LowerGETPCXAndEmitMCInsts(const MachineInstr *MI,
                                    const MCSubtargetInfo &STI);
 
   };
void SparcAsmPrinter::printMemOperand(const MachineInstr *MI, int opNum,
   printOperand(MI, opNum+1, O);
 }
 
 /// PrintAsmOperand - Print out an operand for an inline asm expression.
 ///
 bool SparcAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                       unsigned AsmVariant,
                                       const char *ExtraCode,
-                                      raw_ostream &O) {
+                                      raw_ostream &O,
+                                      StringRef &ErrorMsg) {
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0) return true; // Unknown modifier.
 
     switch (ExtraCode[0]) {
     default:
       // See if this is a generic print operand
-      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O);
+      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O,
+                                         ErrorMsg);
     case 'f':
     case 'r':
      break;
     }
   }
 
   printOperand(MI, OpNo, O);
 

lib/Target/SystemZ/SystemZAsmPrinter.h

SystemZAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
       : AsmPrinter(TM, std::move(Streamer)) {}
 
   // Override AsmPrinter.
   StringRef getPassName() const override { return "SystemZ Assembly Printer"; }
   void EmitInstruction(const MachineInstr *MI) override;
   void EmitMachineConstantPoolValue(MachineConstantPoolValue *MCPV) override;
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        unsigned AsmVariant, const char *ExtraCode,
-                       raw_ostream &OS) override;
+                       raw_ostream &OS, StringRef &ErrorMsg) override;
   bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                              unsigned AsmVariant, const char *ExtraCode,
                              raw_ostream &OS) override;
 };
 } // end namespace llvm
 
 #endif

lib/Target/SystemZ/SystemZAsmPrinter.cpp

EmitMachineConstantPoolValue(MachineConstantPoolValue *MCPV) {
 
   OutStreamer->EmitValue(Expr, Size);
 }
 
 bool SystemZAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
                                         unsigned OpNo,
                                         unsigned AsmVariant,
                                         const char *ExtraCode,
-                                        raw_ostream &OS) {
+                                        raw_ostream &OS,
+                                        StringRef &ErrorMsg) {
   if (ExtraCode && *ExtraCode == 'n') {
     if (!MI->getOperand(OpNo).isImm())
       return true;
     OS << -int64_t(MI->getOperand(OpNo).getImm());
   } else {
     SystemZMCInstLower Lower(MF->getContext(), *this);
     MCOperand MO(Lower.lowerOperand(MI->getOperand(OpNo)));
     SystemZInstPrinter::printOperand(MO, MAI, OS);

lib/Target/X86/X86AsmPrinter.h

public:
   void EmitInstruction(const MachineInstr *MI) override;
 
   void EmitBasicBlockEnd(const MachineBasicBlock &MBB) override {
     SMShadowTracker.emitShadowPadding(*OutStreamer, getSubtargetInfo());
   }
 
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        unsigned AsmVariant, const char *ExtraCode,
-                       raw_ostream &OS) override;
+                       raw_ostream &OS, StringRef &ErrorMsg) override;
   bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                              unsigned AsmVariant, const char *ExtraCode,
                              raw_ostream &OS) override;
 
   /// \brief Return the symbol for the specified constant pool entry.
   MCSymbol *GetCPISymbol(unsigned CPID) const override;
 
   bool doInitialization(Module &M) override {

lib/Target/X86/X86AsmPrinter.cpp

static bool printAsmMRegister(X86AsmPrinter &P, const MachineOperand &MO,
   O << '%' << X86ATTInstPrinter::getRegisterName(Reg);
   return false;
 }
 
 /// PrintAsmOperand - Print out an operand for an inline asm expression.
 ///
 bool X86AsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                     unsigned AsmVariant,
-                                    const char *ExtraCode, raw_ostream &O) {
+                                    const char *ExtraCode, raw_ostream &O,
+                                    StringRef &ErrorMsg) {
   // Does this asm operand have a single letter operand modifier?
   if (ExtraCode && ExtraCode[0]) {
     if (ExtraCode[1] != 0) return true; // Unknown modifier.
 
     const MachineOperand &MO = MI->getOperand(OpNo);
 
     switch (ExtraCode[0]) {
     default:
       // See if this is a generic print operand
-      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O);
+      return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O,
+                                         ErrorMsg);
     case 'a': // This is an address.  Currently only 'i' and 'r' are expected.
       switch (MO.getType()) {
       default:
         return true;
       case MachineOperand::MO_Immediate:
         O << MO.getImm();
         return false;
       case MachineOperand::MO_ConstantPoolIndex:
if (ExtraCode && ExtraCode[0]) {
     case 'n':  // Negate the immediate or print a '-' before the operand.
       // Note: this is a temporary solution. It should be handled target
       // independently as part of the 'MC' work.
       if (MO.isImm()) {
         O << -MO.getImm();
         return false;
       }
       O << '-';
+      break;
+    case 'H':
+      // Diagnostics.
+      // Reaching here means the user asked for the 'H' modifier, on a non
+      // (offsettable) memory operand. Properly report this false behavior.
+      ErrorMsg  = "Cannot use 'H' modifier on a non-offsettable memory "
+                  "reference: ";
+      return true;
     }
   }
 
   printOperand(*this, MI, OpNo, O, /*Modifier*/ nullptr, AsmVariant);
   return false;
 }
 
 bool X86AsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,

lib/Target/XCore/XCoreAsmPrinter.cpp

public:
     void printInlineJT(const MachineInstr *MI, int opNum, raw_ostream &O,
                        const std::string &directive = ".jmptable");
     void printInlineJT32(const MachineInstr *MI, int opNum, raw_ostream &O) {
       printInlineJT(MI, opNum, O, ".jmptable32");
     }
     void printOperand(const MachineInstr *MI, int opNum, raw_ostream &O);
     bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                          unsigned AsmVariant, const char *ExtraCode,
-                         raw_ostream &O) override;
+                         raw_ostream &O,
+                         StringRef &ErrorMsg) override;
     bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNum,
                                unsigned AsmVariant, const char *ExtraCode,
                                raw_ostream &O) override;
 
     void emitArrayBound(MCSymbol *Sym, const GlobalVariable *GV);
     void EmitGlobalVariable(const GlobalVariable *GV) override;
 
     void EmitFunctionEntryLabel() override;
default:
     llvm_unreachable("not implemented");
   }
 }
 
 /// PrintAsmOperand - Print out an operand for an inline asm expression.
 ///
 bool XCoreAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                       unsigned AsmVariant,const char *ExtraCode,
-                                      raw_ostream &O) {
+                                      raw_ostream &O,
+                                      StringRef &ErrorMsg) {
   // Print the operand if there is no operand modifier.
   if (!ExtraCode || !ExtraCode[0]) {
     printOperand(MI, OpNo, O);
     return false;
   }
 
   // Otherwise fallback on the default implementation.
-  return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O);
+  return AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, O,
+                                     ErrorMsg);
 }
 
 bool XCoreAsmPrinter::
 PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNum,
                       unsigned AsmVariant, const char *ExtraCode,
                       raw_ostream &O) {
   if (ExtraCode && ExtraCode[0]) {
     return true; // Unknown modifier.

test/CodeGen/X86/inline-asm-modifier-error.ll

+; RUN: not llc -march x86 < %s 2> %t
+; RUN: FileCheck %s < %t
+
+; 'H' modifier, when applied on a non-memory operand
+; CHECK: error: Cannot use 'H' modifier on a non-offsettable memory reference: 'movl $0, ${1:H}'
+
+define void @foo() local_unnamed_addr #0 {
+entry:
+  tail call void asm sideeffect "movl $0, ${1:H}", "i,i,~{dirflag},~{fpsr},~{flags}"(i32 1, i32 2)
+  ret void
+}
+