[X86][Disassembler] Fix LOCK prefix disassembler support

Summary:
If LOCK prefix is not the first prefix in an instruction, LLVM
disassembler silently drops the prefix.

The fix is to select a proper instruction with a builtin LOCK prefix if
one exists.

Reviewers: craig.topper

Reviewed By: craig.topper

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D49001

llvm-svn: 336400

3 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp b/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
index 80fd080677c..62312777318 100644
--- a/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
+++ b/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
@@ -247,6 +247,8 @@ MCDisassembler::DecodeStatus X86GenericDisassembler::getInstruction(
                  // It should not be 'pause' f3 90
                  InternalInstr.opcode != 0x90)
           Flags |= X86::IP_HAS_REPEAT;
+        if (InternalInstr.hasLockPrefix)
+          Flags |= X86::IP_HAS_LOCK;
       }
       Instr.setFlags(Flags);
     }
diff --git a/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp b/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
index 7badda457f4..1ac304f3be0 100644
--- a/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
+++ b/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
@@ -298,6 +298,9 @@ static bool isREX(struct InternalInstruction *insn, uint8_t prefix) {
 static void setPrefixPresent(struct InternalInstruction *insn, uint8_t prefix) {
   uint8_t nextByte;
   switch (prefix) {
+  case 0xf0:
+    insn->hasLockPrefix = true;
+    break;
   case 0xf2:
   case 0xf3:
     if (lookAtByte(insn, &nextByte))
diff --git a/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.h b/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.h
index c7ad7859967..3b8a4f732ee 100644
--- a/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.h
+++ b/llvm/lib/Target/X86/Disassembler/X86DisassemblerDecoder.h
@@ -563,6 +563,8 @@ struct InternalInstruction {
   bool hasAdSize;
   // Operand-size override
   bool hasOpSize;
+  // Lock prefix
+  bool hasLockPrefix;
   // The repeat prefix if any
   uint8_t repeatPrefix;