[GISel] Make RegBank constructor constexpr. NFC

[topperc]

RegBanks are constructed as global objects. Making the constructor
constexpr helps the compiler constructor it without a global constructor.

clang's optimizer seems to figure this out on its own, but at
least gcc 8 does not.

This is stacked on #71105

[llvmbot]

@llvm/pr-subscribers-llvm-regalloc

Author: Craig Topper (topperc)

Changes

RegBanks are constructed as global objects. Making the constructor
constexpr helps the compiler constructor it without a global constructor.

clang's optimizer seems to figure this out on its own, but at
least gcc 8 does not.

This is stacked on #71105

---

Full diff: https://github.com/llvm/llvm-project/pull/71109.diff

3 Files Affected:

• (modified) llvm/include/llvm/CodeGen/RegisterBank.h (+7-4)
• (modified) llvm/lib/CodeGen/RegisterBank.cpp (+10-14)
• (modified) llvm/utils/TableGen/RegisterBankEmitter.cpp (+1-1)

diff --git a/llvm/include/llvm/CodeGen/RegisterBank.h b/llvm/include/llvm/CodeGen/RegisterBank.h
index ee295c7cdde0048..8915a57b31f6812 100644
--- a/llvm/include/llvm/CodeGen/RegisterBank.h
+++ b/llvm/include/llvm/CodeGen/RegisterBank.h
@@ -13,7 +13,7 @@
 #ifndef LLVM_CODEGEN_REGISTERBANK_H
 #define LLVM_CODEGEN_REGISTERBANK_H
 
-#include "llvm/ADT/BitVector.h"
+#include <cstdint>
 
 namespace llvm {
 // Forward declarations.
@@ -28,8 +28,9 @@ class TargetRegisterInfo;
 class RegisterBank {
 private:
   unsigned ID;
+  unsigned NumRegClasses;
   const char *Name;
-  BitVector ContainedRegClasses;
+  const uint32_t *CoveredClasses;
 
   /// Sentinel value used to recognize register bank not properly
   /// initialized yet.
@@ -39,8 +40,10 @@ class RegisterBank {
   friend RegisterBankInfo;
 
 public:
-  RegisterBank(unsigned ID, const char *Name, const uint32_t *CoveredClasses,
-               unsigned NumRegClasses);
+  constexpr RegisterBank(unsigned ID, const char *Name,
+                         const uint32_t *CoveredClasses, unsigned NumRegClasses)
+      : ID(ID), NumRegClasses(NumRegClasses), Name(Name),
+        CoveredClasses(CoveredClasses) {}
 
   /// Get the identifier of this register bank.
   unsigned getID() const { return ID; }
diff --git a/llvm/lib/CodeGen/RegisterBank.cpp b/llvm/lib/CodeGen/RegisterBank.cpp
index 8e0a0b0dc2824a0..a30e4ac6cfeb317 100644
--- a/llvm/lib/CodeGen/RegisterBank.cpp
+++ b/llvm/lib/CodeGen/RegisterBank.cpp
@@ -22,14 +22,6 @@ using namespace llvm;
 
 const unsigned RegisterBank::InvalidID = UINT_MAX;
 
-RegisterBank::RegisterBank(unsigned ID, const char *Name,
-                           const uint32_t *CoveredClasses,
-                           unsigned NumRegClasses)
-    : ID(ID), Name(Name) {
-  ContainedRegClasses.resize(NumRegClasses);
-  ContainedRegClasses.setBitsInMask(CoveredClasses);
-}
-
 bool RegisterBank::verify(const RegisterBankInfo &RBI,
                           const TargetRegisterInfo &TRI) const {
   assert(isValid() && "Invalid register bank");
@@ -62,13 +54,13 @@ bool RegisterBank::verify(const RegisterBankInfo &RBI,
 
 bool RegisterBank::covers(const TargetRegisterClass &RC) const {
   assert(isValid() && "RB hasn't been initialized yet");
-  return ContainedRegClasses.test(RC.getID());
+  return (CoveredClasses[RC.getID() / 32] & (1U << RC.getID() % 32)) != 0;
 }
 
 bool RegisterBank::isValid() const {
   return ID != InvalidID && Name != nullptr &&
          // A register bank that does not cover anything is useless.
-         !ContainedRegClasses.empty();
+         CoveredClasses != nullptr && NumRegClasses != 0;
 }
 
 bool RegisterBank::operator==(const RegisterBank &OtherRB) const {
@@ -91,15 +83,19 @@ void RegisterBank::print(raw_ostream &OS, bool IsForDebug,
   OS << getName();
   if (!IsForDebug)
     return;
+
+  unsigned Count = 0;
+  for (int i = 0, e = ((NumRegClasses + 31) / 32); i != e; ++i)
+    Count += llvm::popcount(CoveredClasses[i]);
+
   OS << "(ID:" << getID() << ")\n"
      << "isValid:" << isValid() << '\n'
-     << "Number of Covered register classes: " << ContainedRegClasses.count()
-     << '\n';
+     << "Number of Covered register classes: " << Count << '\n';
   // Print all the subclasses if we can.
   // This register classes may not be properly initialized yet.
-  if (!TRI || ContainedRegClasses.empty())
+  if (!TRI || NumRegClasses == 0)
     return;
-  assert(ContainedRegClasses.size() == TRI->getNumRegClasses() &&
+  assert(NumRegClasses == TRI->getNumRegClasses() &&
          "TRI does not match the initialization process?");
   OS << "Covered register classes:\n";
   ListSeparator LS;
diff --git a/llvm/utils/TableGen/RegisterBankEmitter.cpp b/llvm/utils/TableGen/RegisterBankEmitter.cpp
index 60c3fcdba70ed88..f851d9a79870b45 100644
--- a/llvm/utils/TableGen/RegisterBankEmitter.cpp
+++ b/llvm/utils/TableGen/RegisterBankEmitter.cpp
@@ -244,7 +244,7 @@ void RegisterBankEmitter::emitBaseClassImplementation(
   for (const auto &Bank : Banks) {
     std::string QualifiedBankID =
         (TargetName + "::" + Bank.getEnumeratorName()).str();
-    OS << "const RegisterBank " << Bank.getInstanceVarName() << "(/* ID */ "
+    OS << "constexpr RegisterBank " << Bank.getInstanceVarName() << "(/* ID */ "
        << QualifiedBankID << ", /* Name */ \"" << Bank.getName() << "\", "
        << "/* CoveredRegClasses */ " << Bank.getCoverageArrayName()
        << ", /* NumRegClasses */ "