implement mc asmparser support for '.', which gets the

current PC.  rdar://7834775

We now produce an identical .o file compared to the cctools
assembler for something like this:

_f0:
L0:
        jmp L1
        .long . - L0
L1:
        jmp A
        .long . - L1

        .zerofill __DATA,_bss,A,0

llvm-svn: 101227

llvm/include/llvm/MC/MCParser/MCAsmLexer.h

@@ -42,7 +42,7 @@ public:
     Plus, Minus, Tilde,
     Slash,    // '/'
     LParen, RParen, LBrac, RBrac, LCurly, RCurly,
-    Star, Comma, Dollar, Equal, EqualEqual,
+    Star, Dot, Comma, Dollar, Equal, EqualEqual,
     
     Pipe, PipePipe, Caret, 
     Amp, AmpAmp, Exclaim, ExclaimEqual, Percent, Hash,

llvm/lib/MC/MCParser/AsmLexer.cpp

@@ -74,6 +74,11 @@ AsmToken AsmLexer::LexIdentifier() {
   while (isalnum(*CurPtr) || *CurPtr == '_' || *CurPtr == '$' ||
          *CurPtr == '.' || *CurPtr == '@')
     ++CurPtr;
+  
+  // Handle . as a special case.
+  if (CurPtr == TokStart+1 && TokStart[0] == '.')
+    return AsmToken(AsmToken::Dot, StringRef(TokStart, 1));
+  
   return AsmToken(AsmToken::Identifier, StringRef(TokStart, CurPtr - TokStart));
 }
 

llvm/lib/MC/MCParser/AsmParser.cpp

@@ -209,6 +209,7 @@ MCSymbol *AsmParser::CreateSymbol(StringRef Name) {
 ///  primaryexpr ::= (parenexpr
 ///  primaryexpr ::= symbol
 ///  primaryexpr ::= number
+///  primaryexpr ::= '.'
 ///  primaryexpr ::= ~,+,- primaryexpr
 bool AsmParser::ParsePrimaryExpr(const MCExpr *&Res, SMLoc &EndLoc) {
   switch (Lexer.getKind()) {
@@ -253,6 +254,17 @@ bool AsmParser::ParsePrimaryExpr(const MCExpr *&Res, SMLoc &EndLoc) {
     EndLoc = Lexer.getLoc();
     Lex(); // Eat token.
     return false;
+  case AsmToken::Dot: {
+    // This is a '.' reference, which references the current PC.  Emit a
+    // temporary label to the streamer and refer to it.
+    MCSymbol *Sym = Ctx.CreateTempSymbol();
+    Out.EmitLabel(Sym);
+    Res = MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_None, getContext());
+    EndLoc = Lexer.getLoc();
+    Lex(); // Eat identifier.
+    return false;
+  }
+      
   case AsmToken::LParen:
     Lex(); // Eat the '('.
     return ParseParenExpr(Res, EndLoc);

llvm/test/MC/AsmParser/exprs.s

@@ -61,3 +61,14 @@ n:
         
         
         movw	$8, (42)+66(%eax)
+
+// "." support:
+_f0:
+L0:
+        jmp L1
+        .long . - L0
+L1:
+        jmp A
+        .long . - L1
+
+        .zerofill __DATA,_bss,A,0