lib/Parse/ParseStmtAsm.cpp

//===---- ParseStmtAsm.cpp - Assembly Statement Parser --------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements parsing for GCC and Microsoft inline assembly. 
//
//===----------------------------------------------------------------------===//

#include "clang/Parse/Parser.h"
#include "RAIIObjectsForParser.h"
#include "clang/AST/ASTContext.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/TargetInfo.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCInstPrinter.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCParser/MCAsmParser.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCTargetAsmParser.h"
#include "llvm/MC/MCTargetOptions.h"
#include "llvm/Support/SourceMgr.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/TargetSelect.h"
using namespace clang;

namespace {
class ClangAsmParserCallback : public llvm::MCAsmParserSemaCallback {
  Parser &TheParser;
  SourceLocation AsmLoc;
  StringRef AsmString;

  /// The tokens we streamed into AsmString and handed off to MC.
  ArrayRef<Token> AsmToks;

  /// The offset of each token in AsmToks within AsmString.
  ArrayRef<unsigned> AsmTokOffsets;

public:
  ClangAsmParserCallback(Parser &P, SourceLocation Loc, StringRef AsmString,
                         ArrayRef<Token> Toks, ArrayRef<unsigned> Offsets)
      : TheParser(P), AsmLoc(Loc), AsmString(AsmString), AsmToks(Toks),
        AsmTokOffsets(Offsets) {
    assert(AsmToks.size() == AsmTokOffsets.size());
  }

  void *LookupInlineAsmIdentifier(StringRef &LineBuf,
                                  llvm::InlineAsmIdentifierInfo &Info,
                                  bool IsUnevaluatedContext) override {
    // Collect the desired tokens.
    SmallVector<Token, 16> LineToks;
    const Token *FirstOrigToken = nullptr;
    findTokensForString(LineBuf, LineToks, FirstOrigToken);

    unsigned NumConsumedToks;
    ExprResult Result = TheParser.ParseMSAsmIdentifier(
        LineToks, NumConsumedToks, &Info, IsUnevaluatedContext);

    // If we consumed the entire line, tell MC that.
    // Also do this if we consumed nothing as a way of reporting failure.
    if (NumConsumedToks == 0 || NumConsumedToks == LineToks.size()) {
      // By not modifying LineBuf, we're implicitly consuming it all.

      // Otherwise, consume up to the original tokens.
    } else {
      assert(FirstOrigToken && "not using original tokens?");

      // Since we're using original tokens, apply that offset.
      assert(FirstOrigToken[NumConsumedToks].getLocation() ==
             LineToks[NumConsumedToks].getLocation());
      unsigned FirstIndex = FirstOrigToken - AsmToks.begin();
      unsigned LastIndex = FirstIndex + NumConsumedToks - 1;

      // The total length we've consumed is the relative offset
      // of the last token we consumed plus its length.
      unsigned TotalOffset =
          (AsmTokOffsets[LastIndex] + AsmToks[LastIndex].getLength() -
           AsmTokOffsets[FirstIndex]);
      LineBuf = LineBuf.substr(0, TotalOffset);
    }

    // Initialize the "decl" with the lookup result.
    Info.OpDecl = static_cast<void *>(Result.get());
    return Info.OpDecl;
  }

  bool LookupInlineAsmField(StringRef Base, StringRef Member,
                            unsigned &Offset) override {
    return TheParser.getActions().LookupInlineAsmField(Base, Member, Offset,
                                                       AsmLoc);
  }

  static void DiagHandlerCallback(const llvm::SMDiagnostic &D, void *Context) {
    ((ClangAsmParserCallback *)Context)->handleDiagnostic(D);
  }

private:
  /// Collect the appropriate tokens for the given string.
  void findTokensForString(StringRef Str, SmallVectorImpl<Token> &TempToks,
                           const Token *&FirstOrigToken) const {
    // For now, assert that the string we're working with is a substring
    // of what we gave to MC.  This lets us use the original tokens.
    assert(!std::less<const char *>()(Str.begin(), AsmString.begin()) &&
           !std::less<const char *>()(AsmString.end(), Str.end()));

    // Try to find a token whose offset matches the first token.
    unsigned FirstCharOffset = Str.begin() - AsmString.begin();
    const unsigned *FirstTokOffset = std::lower_bound(
        AsmTokOffsets.begin(), AsmTokOffsets.end(), FirstCharOffset);

    // For now, assert that the start of the string exactly
    // corresponds to the start of a token.
    assert(*FirstTokOffset == FirstCharOffset);

    // Use all the original tokens for this line.  (We assume the
    // end of the line corresponds cleanly to a token break.)
    unsigned FirstTokIndex = FirstTokOffset - AsmTokOffsets.begin();
    FirstOrigToken = &AsmToks[FirstTokIndex];
    unsigned LastCharOffset = Str.end() - AsmString.begin();
    for (unsigned i = FirstTokIndex, e = AsmTokOffsets.size(); i != e; ++i) {
      if (AsmTokOffsets[i] >= LastCharOffset)
        break;
      TempToks.push_back(AsmToks[i]);
    }
  }

  void handleDiagnostic(const llvm::SMDiagnostic &D) {
    // Compute an offset into the inline asm buffer.
    // FIXME: This isn't right if .macro is involved (but hopefully, no
    // real-world code does that).
    const llvm::SourceMgr &LSM = *D.getSourceMgr();
    const llvm::MemoryBuffer *LBuf =
        LSM.getMemoryBuffer(LSM.FindBufferContainingLoc(D.getLoc()));
    unsigned Offset = D.getLoc().getPointer() - LBuf->getBufferStart();

    // Figure out which token that offset points into.
    const unsigned *TokOffsetPtr =
        std::lower_bound(AsmTokOffsets.begin(), AsmTokOffsets.end(), Offset);
    unsigned TokIndex = TokOffsetPtr - AsmTokOffsets.begin();
    unsigned TokOffset = *TokOffsetPtr;

    // If we come up with an answer which seems sane, use it; otherwise,
    // just point at the __asm keyword.
    // FIXME: Assert the answer is sane once we handle .macro correctly.
    SourceLocation Loc = AsmLoc;
    if (TokIndex < AsmToks.size()) {
      const Token &Tok = AsmToks[TokIndex];
      Loc = Tok.getLocation();
      Loc = Loc.getLocWithOffset(Offset - TokOffset);
    }
    TheParser.Diag(Loc, diag::err_inline_ms_asm_parsing) << D.getMessage();
  }
};
}

/// Parse an identifier in an MS-style inline assembly block.
///
/// \param CastInfo - a void* so that we don't have to teach Parser.h
///   about the actual type.
ExprResult Parser::ParseMSAsmIdentifier(llvm::SmallVectorImpl<Token> &LineToks,
                                        unsigned &NumLineToksConsumed,
                                        void *CastInfo,
                                        bool IsUnevaluatedContext) {
  llvm::InlineAsmIdentifierInfo &Info =
      *(llvm::InlineAsmIdentifierInfo *)CastInfo;

  // Push a fake token on the end so that we don't overrun the token
  // stream.  We use ';' because it expression-parsing should never
  // overrun it.
  const tok::TokenKind EndOfStream = tok::semi;
  Token EndOfStreamTok;
  EndOfStreamTok.startToken();
  EndOfStreamTok.setKind(EndOfStream);
  LineToks.push_back(EndOfStreamTok);

  // Also copy the current token over.
  LineToks.push_back(Tok);

  PP.EnterTokenStream(LineToks.begin(), LineToks.size(),
                      /*disable macros*/ true,
                      /*owns tokens*/ false);

  // Clear the current token and advance to the first token in LineToks.
  ConsumeAnyToken();

  // Parse an optional scope-specifier if we're in C++.
  CXXScopeSpec SS;
  if (getLangOpts().CPlusPlus) {
    ParseOptionalCXXScopeSpecifier(SS, ParsedType(), /*EnteringContext=*/false);
  }

  // Require an identifier here.
  SourceLocation TemplateKWLoc;
  UnqualifiedId Id;
  bool Invalid =
      ParseUnqualifiedId(SS,
                         /*EnteringContext=*/false,
                         /*AllowDestructorName=*/false,
                         /*AllowConstructorName=*/false,
                         /*ObjectType=*/ParsedType(), TemplateKWLoc, Id);

  // Figure out how many tokens we are into LineToks.
  unsigned LineIndex = 0;
  if (Tok.is(EndOfStream)) {
    LineIndex = LineToks.size() - 2;
  } else {
    while (LineToks[LineIndex].getLocation() != Tok.getLocation()) {
      LineIndex++;
      assert(LineIndex < LineToks.size() - 2); // we added two extra tokens
    }
  }

  // If we've run into the poison token we inserted before, or there
  // was a parsing error, then claim the entire line.
  if (Invalid || Tok.is(EndOfStream)) {
    NumLineToksConsumed = LineToks.size() - 2;
  } else {
    // Otherwise, claim up to the start of the next token.
    NumLineToksConsumed = LineIndex;
  }

  // Finally, restore the old parsing state by consuming all the tokens we
  // staged before, implicitly killing off the token-lexer we pushed.
  for (unsigned i = 0, e = LineToks.size() - LineIndex - 2; i != e; ++i) {
    ConsumeAnyToken();
  }
  assert(Tok.is(EndOfStream));
  ConsumeToken();

  // Leave LineToks in its original state.
  LineToks.pop_back();
  LineToks.pop_back();

  // Perform the lookup.
  return Actions.LookupInlineAsmIdentifier(SS, TemplateKWLoc, Id, Info,
                                           IsUnevaluatedContext);
}

/// Turn a sequence of our tokens back into a string that we can hand
/// to the MC asm parser.
static bool buildMSAsmString(Preprocessor &PP, SourceLocation AsmLoc,
                             ArrayRef<Token> AsmToks,
                             SmallVectorImpl<unsigned> &TokOffsets,
                             SmallString<512> &Asm) {
  assert(!AsmToks.empty() && "Didn't expect an empty AsmToks!");

  // Is this the start of a new assembly statement?
  bool isNewStatement = true;

  for (unsigned i = 0, e = AsmToks.size(); i < e; ++i) {
    const Token &Tok = AsmToks[i];

    // Start each new statement with a newline and a tab.
    if (!isNewStatement && (Tok.is(tok::kw_asm) || Tok.isAtStartOfLine())) {
      Asm += "\n\t";
      isNewStatement = true;
    }

    // Preserve the existence of leading whitespace except at the
    // start of a statement.
    if (!isNewStatement && Tok.hasLeadingSpace())
      Asm += ' ';

    // Remember the offset of this token.
    TokOffsets.push_back(Asm.size());

    // Don't actually write '__asm' into the assembly stream.
    if (Tok.is(tok::kw_asm)) {
      // Complain about __asm at the end of the stream.
      if (i + 1 == e) {
        PP.Diag(AsmLoc, diag::err_asm_empty);
        return true;
      }

      continue;
    }

    // Append the spelling of the token.
    SmallString<32> SpellingBuffer;
    bool SpellingInvalid = false;
    Asm += PP.getSpelling(Tok, SpellingBuffer, &SpellingInvalid);
    assert(!SpellingInvalid && "spelling was invalid after correct parse?");

    // We are no longer at the start of a statement.
    isNewStatement = false;
  }

  // Ensure that the buffer is null-terminated.
  Asm.push_back('\0');
  Asm.pop_back();

  assert(TokOffsets.size() == AsmToks.size());
  return false;
}

/// ParseMicrosoftAsmStatement. When -fms-extensions/-fasm-blocks is enabled,
/// this routine is called to collect the tokens for an MS asm statement.
///
/// [MS]  ms-asm-statement:
///         ms-asm-block
///         ms-asm-block ms-asm-statement
///
/// [MS]  ms-asm-block:
///         '__asm' ms-asm-line '\n'
///         '__asm' '{' ms-asm-instruction-block[opt] '}' ';'[opt]
///
/// [MS]  ms-asm-instruction-block
///         ms-asm-line
///         ms-asm-line '\n' ms-asm-instruction-block
///
StmtResult Parser::ParseMicrosoftAsmStatement(SourceLocation AsmLoc) {
  SourceManager &SrcMgr = PP.getSourceManager();
  SourceLocation EndLoc = AsmLoc;
  SmallVector<Token, 4> AsmToks;

  unsigned BraceNesting = 0;
  unsigned short savedBraceCount = BraceCount;
  bool InAsmComment = false;
  FileID FID;
  unsigned LineNo = 0;
  unsigned NumTokensRead = 0;
  SmallVector<SourceLocation, 4> LBraceLocs;
  bool SkippedStartOfLine = false;

  if (Tok.is(tok::l_brace)) {
    // Braced inline asm: consume the opening brace.
    BraceNesting = 1;
    EndLoc = ConsumeBrace();
    LBraceLocs.push_back(EndLoc);
    ++NumTokensRead;
  } else {
    // Single-line inline asm; compute which line it is on.
    std::pair<FileID, unsigned> ExpAsmLoc =
        SrcMgr.getDecomposedExpansionLoc(EndLoc);
    FID = ExpAsmLoc.first;
    LineNo = SrcMgr.getLineNumber(FID, ExpAsmLoc.second);
    LBraceLocs.push_back(SourceLocation());
  }

  SourceLocation TokLoc = Tok.getLocation();
  do {
    // If we hit EOF, we're done, period.
    if (isEofOrEom())
      break;

    if (!InAsmComment && Tok.is(tok::l_brace)) {
      // Consume the opening brace.
      SkippedStartOfLine = Tok.isAtStartOfLine();
      EndLoc = ConsumeBrace();
      BraceNesting++;
      LBraceLocs.push_back(EndLoc);
      TokLoc = Tok.getLocation();
      ++NumTokensRead;
      continue;
    } else if (!InAsmComment && Tok.is(tok::semi)) {
      // A semicolon in an asm is the start of a comment.
      InAsmComment = true;
      if (BraceNesting) {
        // Compute which line the comment is on.
        std::pair<FileID, unsigned> ExpSemiLoc =
            SrcMgr.getDecomposedExpansionLoc(TokLoc);
        FID = ExpSemiLoc.first;
        LineNo = SrcMgr.getLineNumber(FID, ExpSemiLoc.second);
      }
    } else if (!BraceNesting || InAsmComment) {
      // If end-of-line is significant, check whether this token is on a
      // new line.
      std::pair<FileID, unsigned> ExpLoc =
          SrcMgr.getDecomposedExpansionLoc(TokLoc);
      if (ExpLoc.first != FID ||
          SrcMgr.getLineNumber(ExpLoc.first, ExpLoc.second) != LineNo) {
        // If this is a single-line __asm, we're done.
        if (!BraceNesting)
          break;
        // We're no longer in a comment.
        InAsmComment = false;
      } else if (!InAsmComment && Tok.is(tok::r_brace)) {
        // Single-line asm always ends when a closing brace is seen.
        // FIXME: This is compatible with Apple gcc's -fasm-blocks; what
        // does MSVC do here?
        break;
      }
    }
    if (!InAsmComment && BraceNesting && Tok.is(tok::r_brace) &&
        BraceCount == (savedBraceCount + BraceNesting)) {
      // Consume the closing brace.
      SkippedStartOfLine = Tok.isAtStartOfLine();
      EndLoc = ConsumeBrace();
      BraceNesting--;
      // Finish if all of the opened braces in the inline asm section were
      // consumed.
      if (BraceNesting == 0)
        break;
      else {
        LBraceLocs.pop_back();
        TokLoc = Tok.getLocation();
        ++NumTokensRead;
        continue;
      }
    }

    // Consume the next token; make sure we don't modify the brace count etc.
    // if we are in a comment.
    EndLoc = TokLoc;
    if (InAsmComment)
      PP.Lex(Tok);
    else {
      // Set the token as the start of line if we skipped the original start
      // of line token in case it was a nested brace.
      if (SkippedStartOfLine)
        Tok.setFlag(Token::StartOfLine);
      AsmToks.push_back(Tok);
      ConsumeAnyToken();
    }
    TokLoc = Tok.getLocation();
    ++NumTokensRead;
    SkippedStartOfLine = false;
  } while (1);

  if (BraceNesting && BraceCount != savedBraceCount) {
    // __asm without closing brace (this can happen at EOF).
    for (unsigned i = 0; i < BraceNesting; ++i) {
      Diag(Tok, diag::err_expected) << tok::r_brace;
      Diag(LBraceLocs.back(), diag::note_matching) << tok::l_brace;
      LBraceLocs.pop_back();
    }
    return StmtError();
  } else if (NumTokensRead == 0) {
    // Empty __asm.
    Diag(Tok, diag::err_expected) << tok::l_brace;
    return StmtError();
  }

  // Okay, prepare to use MC to parse the assembly.
  SmallVector<StringRef, 4> ConstraintRefs;
  SmallVector<Expr *, 4> Exprs;
  SmallVector<StringRef, 4> ClobberRefs;

  // We need an actual supported target.
  const llvm::Triple &TheTriple = Actions.Context.getTargetInfo().getTriple();
  llvm::Triple::ArchType ArchTy = TheTriple.getArch();
  const std::string &TT = TheTriple.getTriple();
  const llvm::Target *TheTarget = nullptr;
  bool UnsupportedArch =
      (ArchTy != llvm::Triple::x86 && ArchTy != llvm::Triple::x86_64);
  if (UnsupportedArch) {
    Diag(AsmLoc, diag::err_msasm_unsupported_arch) << TheTriple.getArchName();
  } else {
    std::string Error;
    TheTarget = llvm::TargetRegistry::lookupTarget(TT, Error);
    if (!TheTarget)
      Diag(AsmLoc, diag::err_msasm_unable_to_create_target) << Error;
  }

  assert(!LBraceLocs.empty() && "Should have at least one location here");

  // If we don't support assembly, or the assembly is empty, we don't
  // need to instantiate the AsmParser, etc.
  if (!TheTarget || AsmToks.empty()) {
    return Actions.ActOnMSAsmStmt(AsmLoc, LBraceLocs[0], AsmToks, StringRef(),
                                  /*NumOutputs*/ 0, /*NumInputs*/ 0,
                                  ConstraintRefs, ClobberRefs, Exprs, EndLoc);
  }

  // Expand the tokens into a string buffer.
  SmallString<512> AsmString;
  SmallVector<unsigned, 8> TokOffsets;
  if (buildMSAsmString(PP, AsmLoc, AsmToks, TokOffsets, AsmString))
    return StmtError();

  std::unique_ptr<llvm::MCRegisterInfo> MRI(TheTarget->createMCRegInfo(TT));
  std::unique_ptr<llvm::MCAsmInfo> MAI(TheTarget->createMCAsmInfo(*MRI, TT));
  // Get the instruction descriptor.
  std::unique_ptr<llvm::MCInstrInfo> MII(TheTarget->createMCInstrInfo());
  std::unique_ptr<llvm::MCObjectFileInfo> MOFI(new llvm::MCObjectFileInfo());
  std::unique_ptr<llvm::MCSubtargetInfo> STI(
      TheTarget->createMCSubtargetInfo(TT, "", ""));

  llvm::SourceMgr TempSrcMgr;
  llvm::MCContext Ctx(MAI.get(), MRI.get(), MOFI.get(), &TempSrcMgr);
  llvm::MemoryBuffer *Buffer =
      llvm::MemoryBuffer::getMemBuffer(AsmString, "<MS inline asm>");

  // Tell SrcMgr about this buffer, which is what the parser will pick up.
  TempSrcMgr.AddNewSourceBuffer(Buffer, llvm::SMLoc());

  std::unique_ptr<llvm::MCStreamer> Str(createNullStreamer(Ctx));
  std::unique_ptr<llvm::MCAsmParser> Parser(
      createMCAsmParser(TempSrcMgr, Ctx, *Str.get(), *MAI));

  // FIXME: init MCOptions from sanitizer flags here.
  llvm::MCTargetOptions MCOptions;
  std::unique_ptr<llvm::MCTargetAsmParser> TargetParser(
      TheTarget->createMCAsmParser(*STI, *Parser, *MII, MCOptions));

  std::unique_ptr<llvm::MCInstPrinter> IP(
      TheTarget->createMCInstPrinter(1, *MAI, *MII, *MRI, *STI));

  // Change to the Intel dialect.
  Parser->setAssemblerDialect(1);
  Parser->setTargetParser(*TargetParser.get());
  Parser->setParsingInlineAsm(true);
  TargetParser->setParsingInlineAsm(true);

  ClangAsmParserCallback Callback(*this, AsmLoc, AsmString, AsmToks,
                                  TokOffsets);
  TargetParser->setSemaCallback(&Callback);
  TempSrcMgr.setDiagHandler(ClangAsmParserCallback::DiagHandlerCallback,
                            &Callback);

  unsigned NumOutputs;
  unsigned NumInputs;
  std::string AsmStringIR;
  SmallVector<std::pair<void *, bool>, 4> OpExprs;
  SmallVector<std::string, 4> Constraints;
  SmallVector<std::string, 4> Clobbers;
  if (Parser->parseMSInlineAsm(AsmLoc.getPtrEncoding(), AsmStringIR, NumOutputs,
                               NumInputs, OpExprs, Constraints, Clobbers,
                               MII.get(), IP.get(), Callback))
    return StmtError();

  // Filter out "fpsw".  Clang doesn't accept it, and it always lists flags and
  // fpsr as clobbers.
  auto End = std::remove(Clobbers.begin(), Clobbers.end(), "fpsw");
  Clobbers.erase(End, Clobbers.end());

  // Build the vector of clobber StringRefs.
  ClobberRefs.insert(ClobberRefs.end(), Clobbers.begin(), Clobbers.end());

  // Recast the void pointers and build the vector of constraint StringRefs.
  unsigned NumExprs = NumOutputs + NumInputs;
  ConstraintRefs.resize(NumExprs);
  Exprs.resize(NumExprs);
  for (unsigned i = 0, e = NumExprs; i != e; ++i) {
    Expr *OpExpr = static_cast<Expr *>(OpExprs[i].first);
    if (!OpExpr)
      return StmtError();

    // Need address of variable.
    if (OpExprs[i].second)
      OpExpr =
          Actions.BuildUnaryOp(getCurScope(), AsmLoc, UO_AddrOf, OpExpr).get();

    ConstraintRefs[i] = StringRef(Constraints[i]);
    Exprs[i] = OpExpr;
  }

  // FIXME: We should be passing source locations for better diagnostics.
  return Actions.ActOnMSAsmStmt(AsmLoc, LBraceLocs[0], AsmToks, AsmStringIR,
                                NumOutputs, NumInputs, ConstraintRefs,
                                ClobberRefs, Exprs, EndLoc);
}

/// ParseAsmStatement - Parse a GNU extended asm statement.
///       asm-statement:
///         gnu-asm-statement
///         ms-asm-statement
///
/// [GNU] gnu-asm-statement:
///         'asm' type-qualifier[opt] '(' asm-argument ')' ';'
///
/// [GNU] asm-argument:
///         asm-string-literal
///         asm-string-literal ':' asm-operands[opt]
///         asm-string-literal ':' asm-operands[opt] ':' asm-operands[opt]
///         asm-string-literal ':' asm-operands[opt] ':' asm-operands[opt]
///                 ':' asm-clobbers
///
/// [GNU] asm-clobbers:
///         asm-string-literal
///         asm-clobbers ',' asm-string-literal
///
StmtResult Parser::ParseAsmStatement(bool &msAsm) {
  assert(Tok.is(tok::kw_asm) && "Not an asm stmt");
  SourceLocation AsmLoc = ConsumeToken();

  if (getLangOpts().AsmBlocks && Tok.isNot(tok::l_paren) &&
      !isTypeQualifier()) {
    msAsm = true;
    return ParseMicrosoftAsmStatement(AsmLoc);
  }
  DeclSpec DS(AttrFactory);
  SourceLocation Loc = Tok.getLocation();
  ParseTypeQualifierListOpt(DS, true, false);

  // GNU asms accept, but warn, about type-qualifiers other than volatile.
  if (DS.getTypeQualifiers() & DeclSpec::TQ_const)
    Diag(Loc, diag::w_asm_qualifier_ignored) << "const";
  if (DS.getTypeQualifiers() & DeclSpec::TQ_restrict)
    Diag(Loc, diag::w_asm_qualifier_ignored) << "restrict";
  // FIXME: Once GCC supports _Atomic, check whether it permits it here.
  if (DS.getTypeQualifiers() & DeclSpec::TQ_atomic)
    Diag(Loc, diag::w_asm_qualifier_ignored) << "_Atomic";

  // Remember if this was a volatile asm.
  bool isVolatile = DS.getTypeQualifiers() & DeclSpec::TQ_volatile;
  if (Tok.isNot(tok::l_paren)) {
    Diag(Tok, diag::err_expected_lparen_after) << "asm";
    SkipUntil(tok::r_paren, StopAtSemi);
    return StmtError();
  }
  BalancedDelimiterTracker T(*this, tok::l_paren);
  T.consumeOpen();

  ExprResult AsmString(ParseAsmStringLiteral());
  if (AsmString.isInvalid()) {
    // Consume up to and including the closing paren.
    T.skipToEnd();
    return StmtError();
  }

  SmallVector<IdentifierInfo *, 4> Names;
  ExprVector Constraints;
  ExprVector Exprs;
  ExprVector Clobbers;

  if (Tok.is(tok::r_paren)) {
    // We have a simple asm expression like 'asm("foo")'.
    T.consumeClose();
    return Actions.ActOnGCCAsmStmt(AsmLoc, /*isSimple*/ true, isVolatile,
                                   /*NumOutputs*/ 0, /*NumInputs*/ 0, nullptr,
                                   Constraints, Exprs, AsmString.get(),
                                   Clobbers, T.getCloseLocation());
  }

  // Parse Outputs, if present.
  bool AteExtraColon = false;
  if (Tok.is(tok::colon) || Tok.is(tok::coloncolon)) {
    // In C++ mode, parse "::" like ": :".
    AteExtraColon = Tok.is(tok::coloncolon);
    ConsumeToken();

    if (!AteExtraColon && ParseAsmOperandsOpt(Names, Constraints, Exprs))
      return StmtError();
  }

  unsigned NumOutputs = Names.size();

  // Parse Inputs, if present.
  if (AteExtraColon || Tok.is(tok::colon) || Tok.is(tok::coloncolon)) {
    // In C++ mode, parse "::" like ": :".
    if (AteExtraColon)
      AteExtraColon = false;
    else {
      AteExtraColon = Tok.is(tok::coloncolon);
      ConsumeToken();
    }

    if (!AteExtraColon && ParseAsmOperandsOpt(Names, Constraints, Exprs))
      return StmtError();
  }

  assert(Names.size() == Constraints.size() &&
         Constraints.size() == Exprs.size() && "Input operand size mismatch!");

  unsigned NumInputs = Names.size() - NumOutputs;

  // Parse the clobbers, if present.
  if (AteExtraColon || Tok.is(tok::colon)) {
    if (!AteExtraColon)
      ConsumeToken();

    // Parse the asm-string list for clobbers if present.
    if (Tok.isNot(tok::r_paren)) {
      while (1) {
        ExprResult Clobber(ParseAsmStringLiteral());

        if (Clobber.isInvalid())
          break;

        Clobbers.push_back(Clobber.get());

        if (!TryConsumeToken(tok::comma))
          break;
      }
    }
  }

  T.consumeClose();
  return Actions.ActOnGCCAsmStmt(
      AsmLoc, false, isVolatile, NumOutputs, NumInputs, Names.data(),
      Constraints, Exprs, AsmString.get(), Clobbers, T.getCloseLocation());
}

/// ParseAsmOperands - Parse the asm-operands production as used by
/// asm-statement, assuming the leading ':' token was eaten.
///
/// [GNU] asm-operands:
///         asm-operand
///         asm-operands ',' asm-operand
///
/// [GNU] asm-operand:
///         asm-string-literal '(' expression ')'
///         '[' identifier ']' asm-string-literal '(' expression ')'
///
//
// FIXME: Avoid unnecessary std::string trashing.
bool Parser::ParseAsmOperandsOpt(SmallVectorImpl<IdentifierInfo *> &Names,
                                 SmallVectorImpl<Expr *> &Constraints,
                                 SmallVectorImpl<Expr *> &Exprs) {
  // 'asm-operands' isn't present?
  if (!isTokenStringLiteral() && Tok.isNot(tok::l_square))
    return false;

  while (1) {
    // Read the [id] if present.
    if (Tok.is(tok::l_square)) {
      BalancedDelimiterTracker T(*this, tok::l_square);
      T.consumeOpen();

      if (Tok.isNot(tok::identifier)) {
        Diag(Tok, diag::err_expected) << tok::identifier;
        SkipUntil(tok::r_paren, StopAtSemi);
        return true;
      }

      IdentifierInfo *II = Tok.getIdentifierInfo();
      ConsumeToken();

      Names.push_back(II);
      T.consumeClose();
    } else
      Names.push_back(nullptr);

    ExprResult Constraint(ParseAsmStringLiteral());
    if (Constraint.isInvalid()) {
      SkipUntil(tok::r_paren, StopAtSemi);
      return true;
    }
    Constraints.push_back(Constraint.get());

    if (Tok.isNot(tok::l_paren)) {
      Diag(Tok, diag::err_expected_lparen_after) << "asm operand";
      SkipUntil(tok::r_paren, StopAtSemi);
      return true;
    }

    // Read the parenthesized expression.
    BalancedDelimiterTracker T(*this, tok::l_paren);
    T.consumeOpen();
    ExprResult Res(ParseExpression());
    T.consumeClose();
    if (Res.isInvalid()) {
      SkipUntil(tok::r_paren, StopAtSemi);
      return true;
    }
    Exprs.push_back(Res.get());
    // Eat the comma and continue parsing if it exists.
    if (!TryConsumeToken(tok::comma))
      return false;
  }
}