1 files changed, 40 insertions, 0 deletions
diff --git a/llvm/utils/TableGen/CodeGenTarget.cpp b/llvm/utils/TableGen/CodeGenTarget.cpp
index 47e6934ab36..14822024505 100644
--- a/llvm/utils/TableGen/CodeGenTarget.cpp
+++ b/llvm/utils/TableGen/CodeGenTarget.cpp
@@ -295,6 +295,46 @@ CodeGenRegBank &CodeGenTarget::getRegBank() const {
   return *RegBank;
 }
 
+Optional<CodeGenRegisterClass *>
+CodeGenTarget::getSuperRegForSubReg(const ValueTypeByHwMode &ValueTy,
+                                    CodeGenRegBank &RegBank,
+                                    const CodeGenSubRegIndex *SubIdx) const {
+  std::vector<CodeGenRegisterClass *> Candidates;
+  auto &RegClasses = RegBank.getRegClasses();
+
+  // Try to find a register class which supports ValueTy, and also contains
+  // SubIdx.
+  for (CodeGenRegisterClass &RC : RegClasses) {
+    // Is there a subclass of this class which contains this subregister index?
+    CodeGenRegisterClass *SubClassWithSubReg = RC.getSubClassWithSubReg(SubIdx);
+    if (!SubClassWithSubReg)
+      continue;
+
+    // We have a class. Check if it supports this value type.
+    if (llvm::none_of(SubClassWithSubReg->VTs,
+                      [&ValueTy](const ValueTypeByHwMode &ClassVT) {
+                        return ClassVT == ValueTy;
+                      }))
+      continue;
+
+    // We have a register class which supports both the value type and
+    // subregister index. Remember it.
+    Candidates.push_back(SubClassWithSubReg);
+  }
+
+  // If we didn't find anything, we're done.
+  if (Candidates.empty())
+    return None;
+
+  // Find and return the largest of our candidate classes.
+  llvm::stable_sort(Candidates, [&](const CodeGenRegisterClass *A,
+                                    const CodeGenRegisterClass *B) {
+    return A->getMembers().size() > B->getMembers().size();
+  });
+
+  return Candidates[0];
+}
+
 void CodeGenTarget::ReadRegAltNameIndices() const {
   RegAltNameIndices = Records.getAllDerivedDefinitions("RegAltNameIndex");
   llvm::sort(RegAltNameIndices, LessRecord());