[x86] Add basic support for .code16

This is not really expected to work right yet. Mostly because we will
still emit the OpSize (0x66) prefix in all the wrong places, along with
a number of other corner cases. Those will all be fixed in the subsequent
commits.

Patch from David Woodhouse.

llvm-svn: 198584

1 files changed, 33 insertions, 11 deletions

diff --git a/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp b/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
index 0f8e9f7b4ad..86ba1858190 100644
--- a/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ b/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -544,9 +544,21 @@ private:
     // FIXME: Can tablegen auto-generate this?
     return (STI.getFeatureBits() & X86::Mode64Bit) != 0;
   }
-  void SwitchMode() {
-    unsigned FB = ComputeAvailableFeatures(STI.ToggleFeature(X86::Mode64Bit));
+  bool is32BitMode() const {
+    // FIXME: Can tablegen auto-generate this?
+    return (STI.getFeatureBits() & X86::Mode32Bit) != 0;
+  }
+  bool is16BitMode() const {
+    // FIXME: Can tablegen auto-generate this?
+    return (STI.getFeatureBits() & X86::Mode16Bit) != 0;
+  }
+  void SwitchMode(uint64_t mode) {
+    uint64_t oldMode = STI.getFeatureBits() &
+        (X86::Mode64Bit | X86::Mode32Bit | X86::Mode16Bit);
+    unsigned FB = ComputeAvailableFeatures(STI.ToggleFeature(oldMode | mode));
     setAvailableFeatures(FB);
+    assert(mode == (STI.getFeatureBits() &
+                    (X86::Mode64Bit | X86::Mode32Bit | X86::Mode16Bit)));
   }
 
   bool isParsingIntelSyntax() {
@@ -1033,7 +1045,8 @@ struct X86Operand : public MCParsedAsmOperand {
 } // end anonymous namespace.
 
 bool X86AsmParser::isSrcOp(X86Operand &Op) {
-  unsigned basereg = is64BitMode() ? X86::RSI : X86::ESI;
+  unsigned basereg =
+      is64BitMode() ? X86::RSI : (is32BitMode() ? X86::ESI : X86::SI);
 
   return (Op.isMem() &&
     (Op.Mem.SegReg == 0 || Op.Mem.SegReg == X86::DS) &&
@@ -1043,7 +1056,8 @@ bool X86AsmParser::isSrcOp(X86Operand &Op) {
 }
 
 bool X86AsmParser::isDstOp(X86Operand &Op) {
-  unsigned basereg = is64BitMode() ? X86::RDI : X86::EDI;
+  unsigned basereg =
+      is64BitMode() ? X86::RDI : (is32BitMode() ? X86::EDI : X86::DI);
 
   return Op.isMem() &&
     (Op.Mem.SegReg == 0 || Op.Mem.SegReg == X86::ES) &&
@@ -1193,7 +1207,8 @@ X86AsmParser::CreateMemForInlineAsm(unsigned SegReg, const MCExpr *Disp,
     // operand to ensure proper matching.  Just pick a GPR based on the size of
     // a pointer.
     if (!Info.IsVarDecl) {
-      unsigned RegNo = is64BitMode() ? X86::RBX : X86::EBX;
+      unsigned RegNo =
+          is64BitMode() ? X86::RBX : (is32BitMode() ? X86::EBX : X86::BX);
       return X86Operand::CreateReg(RegNo, Start, End, /*AddressOf=*/true,
                                    SMLoc(), Identifier, Info.OpDecl);
     }
@@ -1612,7 +1627,8 @@ X86Operand *X86AsmParser::ParseIntelOffsetOfOperator() {
   // The offset operator will have an 'r' constraint, thus we need to create
   // register operand to ensure proper matching.  Just pick a GPR based on
   // the size of a pointer.
-  unsigned RegNo = is64BitMode() ? X86::RBX : X86::EBX;
+  unsigned RegNo =
+      is64BitMode() ? X86::RBX : (is32BitMode() ? X86::EBX : X86::BX);
   return X86Operand::CreateReg(RegNo, Start, End, /*GetAddress=*/true,
                                OffsetOfLoc, Identifier, Info.OpDecl);
 }
@@ -2679,18 +2695,24 @@ bool X86AsmParser::ParseDirectiveWord(unsigned Size, SMLoc L) {
 }
 
 /// ParseDirectiveCode
-///  ::= .code32 | .code64
+///  ::= .code16 | .code32 | .code64
 bool X86AsmParser::ParseDirectiveCode(StringRef IDVal, SMLoc L) {
-  if (IDVal == ".code32") {
+  if (IDVal == ".code16") {
+    Parser.Lex();
+    if (!is16BitMode()) {
+      SwitchMode(X86::Mode16Bit);
+      getParser().getStreamer().EmitAssemblerFlag(MCAF_Code16);
+    }
+  } else  if (IDVal == ".code32") {
     Parser.Lex();
-    if (is64BitMode()) {
-      SwitchMode();
+    if (!is32BitMode()) {
+      SwitchMode(X86::Mode32Bit);
       getParser().getStreamer().EmitAssemblerFlag(MCAF_Code32);
     }
   } else if (IDVal == ".code64") {
     Parser.Lex();
     if (!is64BitMode()) {
-      SwitchMode();
+      SwitchMode(X86::Mode64Bit);
       getParser().getStreamer().EmitAssemblerFlag(MCAF_Code64);
     }
   } else {