From faf72ffda3bf83b08769428129ee4755787ee6cf Mon Sep 17 00:00:00 2001
From: Kevin Enderby <enderby@apple.com>
Date: Fri, 9 Mar 2012 17:52:49 +0000
Subject: [PATCH] Fix the x86 disassembler to at least print the lock prefix if
 it is the first prefix.  Added a FIXME to remind us this still does not work
 when it is not the first prefix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152414 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/X86/Disassembler/X86DisassemblerDecoder.c | 7 +++++++
 test/MC/Disassembler/X86/simple-tests.txt            | 5 +++++
 utils/TableGen/X86RecognizableInstr.cpp              | 6 +++---
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c b/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c
index b0e66f00c71..6f7e8f23466 100644
--- a/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c
+++ b/lib/Target/X86/Disassembler/X86DisassemblerDecoder.c
@@ -312,6 +312,13 @@ static int readPrefixes(struct InternalInstruction* insn) {
     
     if (consumeByte(insn, &byte))
       return -1;
+
+    // If the the first byte is a LOCK prefix break and let it be disassembled
+    // as a lock "instruction", by creating an <MCInst #xxxx LOCK_PREFIX>.
+    // FIXME there is currently no way to get the disassembler to print the
+    // lock prefix if it is not the first byte.
+    if (insn->readerCursor - 1 == insn->startLocation && byte == 0xf0)
+      break;
     
     switch (byte) {
     case 0xf0:  /* LOCK */
diff --git a/test/MC/Disassembler/X86/simple-tests.txt b/test/MC/Disassembler/X86/simple-tests.txt
index 840d5fab2dc..414c5d5fe9e 100644
--- a/test/MC/Disassembler/X86/simple-tests.txt
+++ b/test/MC/Disassembler/X86/simple-tests.txt
@@ -724,3 +724,8 @@
 
 # CHECK: vpermil2ps $1, 4(%rax), %xmm2, %xmm3, %xmm0
 0xc4 0xe3 0xe1 0x48 0x40 0x04 0x21
+
+# rdar://8812056 lldb doesn't print the x86 lock prefix when disassembling
+# CHECK: lock
+# CHECK: xaddq	%rcx, %rbx
+0xf0 0x48 0x0f 0xc1 0xcb
diff --git a/utils/TableGen/X86RecognizableInstr.cpp b/utils/TableGen/X86RecognizableInstr.cpp
index 5bf473d95e0..6bbc929d26d 100644
--- a/utils/TableGen/X86RecognizableInstr.cpp
+++ b/utils/TableGen/X86RecognizableInstr.cpp
@@ -405,13 +405,13 @@ RecognizableInstr::filter_ret RecognizableInstr::filter() const {
     return FILTER_STRONG;
     
     
-  // Filter out artificial instructions
+  // Filter out artificial instructions but leave in the LOCK_PREFIX so it is
+  // printed as a separate "instruction".
     
   if (Name.find("_Int") != Name.npos       ||
       Name.find("Int_") != Name.npos       ||
       Name.find("_NOREX") != Name.npos     ||
-      Name.find("2SDL") != Name.npos       ||
-      Name == "LOCK_PREFIX")
+      Name.find("2SDL") != Name.npos)
     return FILTER_STRONG;
 
   // Filter out instructions with segment override prefixes.