diff --git a/llvm/lib/Target/X86/AsmParser/X86Operand.h b/llvm/lib/Target/X86/AsmParser/X86Operand.h
--- a/llvm/lib/Target/X86/AsmParser/X86Operand.h
+++ b/llvm/lib/Target/X86/AsmParser/X86Operand.h
@@ -383,6 +383,8 @@
   bool isMem512_GR16() const {
     if (!isMem512())
       return false;
+    if (getMemBaseReg() == X86::AH)
+      return true;
     if (getMemBaseReg() &&
         !X86MCRegisterClasses[X86::GR16RegClassID].contains(getMemBaseReg()))
       return false;
@@ -391,6 +393,8 @@
   bool isMem512_GR32() const {
     if (!isMem512())
       return false;
+    if (getMemBaseReg() == X86::AH)
+      return true;
     if (getMemBaseReg() &&
         !X86MCRegisterClasses[X86::GR32RegClassID].contains(getMemBaseReg()) &&
         getMemBaseReg() != X86::EIP)
@@ -404,6 +408,8 @@
   bool isMem512_GR64() const {
     if (!isMem512())
       return false;
+    if (getMemBaseReg() == X86::AH)
+      return true;
     if (getMemBaseReg() &&
         !X86MCRegisterClasses[X86::GR64RegClassID].contains(getMemBaseReg()) &&
         getMemBaseReg() != X86::RIP)