[X86][inline asm] support even directive

[m_zuckerman]

Summary

The .even directive aligns content to an evan-numbered address.

In at&t syntax .even
In Microsoft syntax even (without the dot).

[rnk]

lgtm

include/llvm/MC/MCTargetAsmParser.h

 class StringRef;
 template <typename T> class SmallVectorImpl;
 
 typedef SmallVectorImpl<std::unique_ptr<MCParsedAsmOperand>> OperandVector;
 
 enum AsmRewriteKind {
   AOK_Delete = 0,     // Rewrite should be ignored.
   AOK_Align,          // Rewrite align as .align.
+  AOK_EVEN,           // Rewrite even as .even.
   AOK_DotOperator,    // Rewrite a dot operator expression as an immediate.
                       // E.g., [eax].foo.bar -> [eax].8
   AOK_Emit,           // Rewrite _emit as .byte.
   AOK_Imm,            // Rewrite as $$N.
   AOK_ImmPrefix,      // Add $$ before a parsed Imm.
   AOK_Input,          // Rewrite in terms of $N.
   AOK_Output,         // Rewrite in terms of $N.
   AOK_SizeDirective,  // Add a sizing directive (e.g., dword ptr).

lib/MC/MCParser/AsmParser.cpp

bool AsmParser::parseStatement(ParseStatementInfo &Info,
   if (ParsingInlineAsm && (IDVal == "_emit" || IDVal == "__emit" ||
                            IDVal == "_EMIT" || IDVal == "__EMIT"))
     return parseDirectiveMSEmit(IDLoc, Info, IDVal.size());
 
   // __asm align
   if (ParsingInlineAsm && (IDVal == "align" || IDVal == "ALIGN"))
     return parseDirectiveMSAlign(IDLoc, Info);
 
+  if (ParsingInlineAsm && (IDVal == "even"))
+    Info.AsmRewrites->emplace_back(AOK_EVEN, IDLoc, 4);
   checkForValidSection();
 
   // Canonicalize the opcode to lower case.
   std::string OpcodeStr = IDVal.lower();
   ParseInstructionInfo IInfo(Info.AsmRewrites);
   bool HadError = getTargetParser().ParseInstruction(IInfo, OpcodeStr, IDLoc,
                                                      Info.ParsedOperands);
   Info.ParseError = HadError;
case AOK_Align: {
       unsigned Val = AR.Val;
       OS << ".align " << Val;
 
       // Skip the original immediate.
       assert(Val < 10 && "Expected alignment less then 2^10.");
       AdditionalSkip = (Val < 4) ? 2 : Val < 7 ? 3 : 4;
       break;
     }
+    case AOK_EVEN:
+      OS << ".even";
+      break;
     case AOK_DotOperator:
       // Insert the dot if the user omitted it.
       OS.flush();
       if (AsmStringIR.back() != '.')
         OS << '.';
       OS << AR.Val;
       break;
     }

lib/Target/X86/AsmParser/X86AsmParser.cpp

 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCParser/MCAsmLexer.h"
 #include "llvm/MC/MCParser/MCAsmParser.h"
 #include "llvm/MC/MCParser/MCParsedAsmOperand.h"
 #include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/MCTargetAsmParser.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
private:
   std::unique_ptr<X86Operand> ParseMemOperand(unsigned SegReg, SMLoc StartLoc);
 
   std::unique_ptr<X86Operand>
   CreateMemForInlineAsm(unsigned SegReg, const MCExpr *Disp, unsigned BaseReg,
                         unsigned IndexReg, unsigned Scale, SMLoc Start,
                         SMLoc End, unsigned Size, StringRef Identifier,
                         InlineAsmIdentifierInfo &Info);
 
+  bool parseDirectiveEven(SMLoc L);
   bool ParseDirectiveWord(unsigned Size, SMLoc L);
   bool ParseDirectiveCode(StringRef IDVal, SMLoc L);
 
   bool processInstruction(MCInst &Inst, const OperandVector &Ops);
 
   /// Wrapper around MCStreamer::EmitInstruction(). Possibly adds
   /// instrumentation around Inst.
   void EmitInstruction(MCInst &Inst, OperandVector &Operands, MCStreamer &Out);
if (getLexer().isNot(AsmToken::EndOfStatement)) {
       if (Parser.getTok().getString() == "noprefix")
         Parser.Lex();
       else if (Parser.getTok().getString() == "prefix")
         return Error(DirectiveID.getLoc(), "'.intel_syntax prefix' is not "
                                            "supported: registers must not have "
                                            "a '%' prefix in .intel_syntax");
     }
     return false;
-  }
+  } else if (IDVal == ".even")
+    return parseDirectiveEven(DirectiveID.getLoc());
   return true;
 }
 
+/// parseDirectiveEven
+///  ::= .even
+bool X86AsmParser::parseDirectiveEven(SMLoc L) {
+  const MCSection *Section = getStreamer().getCurrentSection().first;
+  MCAsmParser &Parser = getParser();
+  if (getLexer().isNot(AsmToken::EndOfStatement)) {
+    TokError("unexpected token in directive");
+    return false;
+    
+  }
+  if (!Section) {
+    getStreamer().InitSections(false);
+    Section = getStreamer().getCurrentSection().first;
+  }
+  if (Section->UseCodeAlign())
+    getStreamer().EmitCodeAlignment(2, 0);
+  else
+    getStreamer().EmitValueToAlignment(2, 0, 1, 0);
+  return false;
+}
 /// ParseDirectiveWord
 ///  ::= .word [ expression (, expression)* ]
 bool X86AsmParser::ParseDirectiveWord(unsigned Size, SMLoc L) {
   MCAsmParser &Parser = getParser();
   if (getLexer().isNot(AsmToken::EndOfStatement)) {
     for (;;) {
       const MCExpr *Value;
       SMLoc ExprLoc = getLexer().getLoc();

test/MC/X86/x86-evenDirective.s

+# RUN: llvm-mc -filetype obj -o - %s | llvm-readobj -s -sd \
+# RUN:   | FileCheck %s
+
+  .text
+  even_check:
+  .byte 0x00
+  .byte 0x01
+  .byte 0x02
+  .byte 0x03
+  .byte 0x04
+  .byte 0x05
+  .byte 0x06
+  .byte 0x07
+  .byte 0x08
+  .byte 0x09
+  .byte 0x10
+  .even
+  .byte 0x11
+  .byte 0x12
+  .even
+  .byte 0x13
+  .even
+  .byte 0x00
+  .byte 0x01
+  .byte 0x02
+  .byte 0x03
+  .byte 0x04
+  .byte 0x05
+  .byte 0x06
+  .byte 0x07
+  .byte 0x08
+  .byte 0x09
+  .byte 0x10
+  .byte 0x11
+  .byte 0x12
+  .byte 0x13
+  .byte 0x14
+  .byte 0x15
+
+# CHECK: Section {
+# CHECK:   Name: .text
+# CHECK:   SectionData (
+# CHECK:      0000: 00010203 04050607 08091090 11121390
+# CHECK:    0010: 00010203 04050607 08091011 12131415
+# CHECK:   )
+# CHECK: }
+
+
+
+