[llvm] [X86][MC] Support Intel FRED and LKGS instructions. (PR #91909)

[Shengchen Kan via llvm-commits]

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@@ -0,0 +1,35 @@
+# RUN: llvm-mc --disassemble %s -triple=x86_64 | FileCheck %s --check-prefixes=ATT
+# RUN: llvm-mc --disassemble %s -triple=x86_64 --output-asm-variant=1 | FileCheck %s --check-prefixes=INTEL
+
+# ATT:   lkgsw %ax
+# INTEL: lkgs ax
+0xf2,0x0f,0x00,0xf0
+
+# ATT:   lkgsw %r12w
+# INTEL: lkgs r12w
+0xf2,0x41,0x0f,0x00,0xf4
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KanRobert wrote:

Never mind. It's correct.

> the REX prefix byte must immediately precede the opcode
> byte or the escape opcode byte (0FH). 

https://github.com/llvm/llvm-project/pull/91909