[RegisterBank] Provide a way to check if a register bank is valid.

Change the default constructor to create invalid object.
The target will have to properly initialize the register banks before
using them.

llvm-svn: 265460

1 files changed, 12 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/RegisterBank.cpp b/llvm/lib/CodeGen/GlobalISel/RegisterBank.cpp
index 5c86e426e1b..4e0aa080039 100644
--- a/llvm/lib/CodeGen/GlobalISel/RegisterBank.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/RegisterBank.cpp
@@ -18,6 +18,10 @@
 
 using namespace llvm;
 
+const unsigned RegisterBank::InvalidID = UINT_MAX;
+
+RegisterBank::RegisterBank() : ID(InvalidID), Name(nullptr), Size(0) {}
+
 void RegisterBank::verify(const TargetRegisterInfo &TRI) const {
   // Verify that the Size of the register bank is big enough to cover all the
   // register classes it covers.
@@ -26,7 +30,14 @@ void RegisterBank::verify(const TargetRegisterInfo &TRI) const {
 }
 
 bool RegisterBank::contains(const TargetRegisterClass &RC) const {
-  return ContainedRegClass.test(RC.getID());
+  assert(isValid() && "RB hasn't been initialized yet");
+  return ContainedRegClasses.test(RC.getID());
+}
+
+bool RegisterBank::isValid() const {
+  return ID != InvalidID && Name != nullptr && Size != 0 &&
+         // A register bank that does not cover anything is useless.
+         !ContainedRegClasses.empty();
 }
 
 bool RegisterBank::operator==(const RegisterBank &OtherRB) const {