[x86] Fix 16-bit handling of OpSize bit

When disassembling in 16-bit mode the meaning of the OpSize bit is
inverted. Instructions found in the IC_OPSIZE context will actually
*not* have the 0x66 prefix, and instructions in the IC context will
have the 0x66 prefix. Make use of the existing special-case handling
for the 0x66 prefix being in the wrong place, to cope with this.

llvm-svn: 199650

1 files changed, 5 insertions, 3 deletions

diff --git a/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c b/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c
index fc19650c7bc..66badd95c32 100644
--- a/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c
+++ b/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c
@@ -971,7 +971,7 @@ static int getID(struct InternalInstruction* insn, const void *miiArg) {
     }
   }
   else {
-    if (isPrefixAtLocation(insn, 0x66, insn->necessaryPrefixLocation))
+    if (insn->mode != MODE_16BIT && isPrefixAtLocation(insn, 0x66, insn->necessaryPrefixLocation))
       attrMask |= ATTR_OPSIZE;
     else if (isPrefixAtLocation(insn, 0x67, insn->necessaryPrefixLocation))
       attrMask |= ATTR_ADSIZE;
@@ -989,7 +989,8 @@ static int getID(struct InternalInstruction* insn, const void *miiArg) {
 
   /* The following clauses compensate for limitations of the tables. */
 
-  if (insn->prefixPresent[0x66] && !(attrMask & ATTR_OPSIZE)) {
+  if ((insn->mode == MODE_16BIT || insn->prefixPresent[0x66]) &&
+      !(attrMask & ATTR_OPSIZE)) {
     /*
      * The instruction tables make no distinction between instructions that
      * allow OpSize anywhere (i.e., 16-bit operations) and that need it in a
@@ -1021,7 +1022,8 @@ static int getID(struct InternalInstruction* insn, const void *miiArg) {
     specWithOpSizeName =
       x86DisassemblerGetInstrName(instructionIDWithOpsize, miiArg);
 
-    if (is16BitEquivalent(specName, specWithOpSizeName)) {
+    if (is16BitEquivalent(specName, specWithOpSizeName) &&
+        (insn->mode == MODE_16BIT) ^ insn->prefixPresent[0x66]) {
       insn->instructionID = instructionIDWithOpsize;
       insn->spec = specifierForUID(instructionIDWithOpsize);
     } else {