Update the X86 disassembler to use xacquire and xrelease when appropriate.

This is a bit tricky as the xacquire and xrelease hints use the same bytes,
0xf2 and 0xf3, as the repne and rep prefixes.

Fortunately llvm has different llvm MCInst Opcode enums for rep/xrelease
and repne/xacquire. So to make this work a boolean was added the
InternalInstruction struct as part of the Prefix state which is set with the
added logic in readPrefixes() when decoding an instruction to determine
if these prefix bytes are to be disassembled as xacquire or xrelease.  Then
we let the matcher pick the normal prefix instructionID and we change the
Opcode after that when it is set into the MCInst being created.

rdar://11019859


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184490 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 0 deletions

diff --git a/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c b/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c
index e40edba6d6..55ab8ebe7b 100644
--- a/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c
+++ b/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c
@@ -328,6 +328,27 @@ static int readPrefixes(struct InternalInstruction* insn) {
         break;
       if (lookAtByte(insn, &nextByte))
         return -1;
+      /*
+       * If the byte is 0xf2 or 0xf3, and any of the following conditions are
+       * met:
+       * - it is followed by a LOCK (0xf0) prefix
+       * - it is followed by an xchg instruction
+       * then it should be disassembled as a xacquire/xrelease not repne/rep.
+       */
+      if ((byte == 0xf2 || byte == 0xf3) &&
+          ((nextByte == 0xf0) |
+          ((nextByte & 0xfe) == 0x86 || (nextByte & 0xf8) == 0x90)))
+        insn->xAcquireRelease = TRUE;
+      /*
+       * Also if the byte is 0xf3, and the following condition is met:
+       * - it is followed by a "mov mem, reg" (opcode 0x88/0x89) or
+       *                       "mov mem, imm" (opcode 0xc6/0xc7) instructions.
+       * then it should be disassembled as an xrelease not rep.
+       */
+      if (byte == 0xf3 &&
+          (nextByte == 0x88 || nextByte == 0x89 ||
+           nextByte == 0xc6 || nextByte == 0xc7))
+        insn->xAcquireRelease = TRUE;
       if (insn->mode == MODE_64BIT && (nextByte & 0xf0) == 0x40) {
         if (consumeByte(insn, &nextByte))
           return -1;