Restore LOW32_ADDR_ACCESSRegClass definition

Somehow there are code changes in tests when unused.

Author: arsenm

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -61512,7 +61512,8 @@ static bool isGRClass(const TargetRegisterClass &RC) {
   return RC.hasSuperClassEq(&X86::GR8RegClass) ||
          RC.hasSuperClassEq(&X86::GR16RegClass) ||
          RC.hasSuperClassEq(&X86::GR32RegClass) ||
-         RC.hasSuperClassEq(&X86::GR64RegClass);
+         RC.hasSuperClassEq(&X86::GR64RegClass) ||
+         RC.hasSuperClassEq(&X86::LOW32_ADDR_ACCESS_RBPRegClass);
 }
 
 /// Check if \p RC is a vector register class.

llvm/lib/Target/X86/X86RegisterInfo.td

@@ -716,6 +716,10 @@ def GR64_NOREX2_NOSP : RegisterClass<"X86", [i64], 64,
 // which we do not have right now.
 def LOW32_ADDR_ACCESS : RegisterClass<"X86", [i32], 32, (add GR32, RIP)>;
 
+// FIXME: This is unused, but deleting it results in codegen changes
+def LOW32_ADDR_ACCESS_RBP : RegisterClass<"X86", [i32], 32,
+                                          (add LOW32_ADDR_ACCESS, RBP)>;
+
 // A class to support the 'A' assembler constraint: [ER]AX then [ER]DX.
 def GR32_AD : RegisterClass<"X86", [i32], 32, (add EAX, EDX)>;
 def GR64_AD : RegisterClass<"X86", [i64], 64, (add RAX, RDX)>;